Merge remote-tracking branch 'origin/dev' into mp-samplers

# Conflicts:
#	kmath-coroutines/src/commonMain/kotlin/scientifik/kmath/chains/BlockingIntChain.kt
#	kmath-coroutines/src/commonMain/kotlin/scientifik/kmath/chains/BlockingRealChain.kt
#	kmath-coroutines/src/commonMain/kotlin/scientifik/kmath/chains/Chain.kt
#	kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/RandomChain.kt

CHANGELOG.md

@@ -0,0 +1,38 @@
+# KMath
+
+## [Unreleased]
+
+### Added
+- Functional Expressions API
+- Mathematical Syntax Tree, its interpreter and API
+- String to MST parser (https://github.com/mipt-npm/kmath/pull/120)
+- MST to JVM bytecode translator (https://github.com/mipt-npm/kmath/pull/94)
+- FloatBuffer (specialized MutableBuffer over FloatArray)
+- FlaggedBuffer to associate primitive numbers buffer with flags (to mark values infinite or missing, etc.)
+- Specialized builder functions for all primitive buffers like `IntBuffer(25) { it + 1 }` (https://github.com/mipt-npm/kmath/pull/125)
+- Interface `NumericAlgebra` where `number` operation is available to convert numbers to algebraic elements
+- Inverse trigonometric functions support in ExtendedField (`asin`, `acos`, `atan`) (https://github.com/mipt-npm/kmath/pull/114)
+- New space extensions: `average` and `averageWith`
+- Local coding conventions
+- Geometric Domains API in `kmath-core`
+- Blocking chains in `kmath-coroutines`
+- Full hyperbolic functions support and default implementations within `ExtendedField`
+- Norm support for `Complex`
+
+### Changed
+- `readAsMemory` now has `throws IOException` in JVM signature.
+- Several functions taking functional types were made `inline`.
+- Several functions taking functional types now have `callsInPlace` contracts.
+- BigInteger and BigDecimal algebra: JBigDecimalField has companion object with default math context; minor optimizations
+- `power(T, Int)` extension function has preconditions and supports `Field<T>`
+- Memory objects have more preconditions (overflow checking)
+- `tg` function is renamed to `tan` (https://github.com/mipt-npm/kmath/pull/114)
+- Gradle version: 6.3 -> 6.6
+- Moved probability distributions to commons-rng and to `kmath-prob`
+
+### Fixed
+- Missing copy method in Memory implementation on JS (https://github.com/mipt-npm/kmath/pull/106)
+- D3.dim value in `kmath-dimensions`
+- Multiplication in integer rings in `kmath-core` (https://github.com/mipt-npm/kmath/pull/101)
+- Commons RNG compatibility (https://github.com/mipt-npm/kmath/issues/93)
+- Multiplication of BigInt by scalar

README.md

@@ -5,12 +5,17 @@
 
 Bintray:        [ ![Download](https://api.bintray.com/packages/mipt-npm/scientifik/kmath-core/images/download.svg) ](https://bintray.com/mipt-npm/scientifik/kmath-core/_latestVersion)
 
-Bintray-dev:    [ ![Download](https://api.bintray.com/packages/mipt-npm/dev/kmath-core/images/download.svg) ](https://bintray.com/mipt-npm/scientifik/kmath-core/_latestVersion)
+Bintray-dev:    [ ![Download](https://api.bintray.com/packages/mipt-npm/dev/kmath-core/images/download.svg) ](https://bintray.com/mipt-npm/dev/kmath-core/_latestVersion)
 
 # KMath
 Could be pronounced as `key-math`.
 The Kotlin MATHematics library is intended as a Kotlin-based analog to Python's `numpy` library. In contrast to `numpy` and `scipy` it is modular and has a lightweight core.
 
+## Publications
+* [A conceptual article about context-oriented design](https://proandroiddev.com/an-introduction-context-oriented-programming-in-kotlin-2e79d316b0a2)
+* [Another article about context-oriented design](https://proandroiddev.com/diving-deeper-into-context-oriented-programming-in-kotlin-3ecb4ec38814)
+* [ACAT 2019 conference paper](https://aip.scitation.org/doi/abs/10.1063/1.5130103)
+
 # Goal
 * Provide a flexible and powerful API to work with mathematics abstractions in Kotlin-multiplatform (JVM and JS for now and Native in future). 
 * Provide basic multiplatform implementations for those abstractions (without significant performance optimization).

build.gradle.kts

@@ -11,6 +11,7 @@ allprojects {
     repositories {
         jcenter()
         maven("https://dl.bintray.com/kotlin/kotlinx")
+        maven("https://dl.bintray.com/hotkeytlt/maven")
     }
 
     group = "scientifik"

doc/algebra.md

@@ -1,110 +1,124 @@
-# Algebra and algebra elements
+# Algebraic Structures and Algebraic Elements
 
-The mathematical operations in `kmath` are generally separated from mathematical objects.
-This means that in order to perform an operation, say `+`, one needs two objects of a type `T` and
-and algebra context which defines appropriate operation, say `Space<T>`. Next one needs to run actual operation
-in the context:
+The mathematical operations in KMath are generally separated from mathematical objects. This means that to perform an 
+operation, say `+`, one needs two objects of a type `T` and an algebra context, which draws appropriate operation up, 
+say `Space<T>`. Next one needs to run the actual operation in the context:
 
 ```kotlin
-val a: T
-val b: T
-val space: Space<T>
+import scientifik.kmath.operations.*
 
-val c = space.run{a + b}
+val a: T = ...
+val b: T = ...
+val space: Space<T> = ...
+
+val c = space { a + b }
 ```
 
-From the first glance, this distinction seems to be a needless complication, but in fact one needs
-to remember that in mathematics, one could define different operations on the same objects. For example,
-one could use different types of geometry for vectors.
+At first glance, this distinction seems to be a needless complication, but in fact one needs to remember that in 
+mathematics, one could draw up different operations on same objects. For example, one could use different types of 
+geometry for vectors.
 
-## Algebra hierarchy
+## Algebraic Structures
 
 Mathematical contexts have the following hierarchy:
 
-**Space** <- **Ring** <- **Field**
+**Algebra** ← **Space** ← **Ring** ← **Field**
 
-All classes follow abstract mathematical constructs.
-[Space](http://mathworld.wolfram.com/Space.html) defines `zero` element, addition operation and multiplication by constant,
-[Ring](http://mathworld.wolfram.com/Ring.html) adds multiplication and unit `one` element,
-[Field](http://mathworld.wolfram.com/Field.html) adds division operation.
+These interfaces follow real algebraic structures:
 
-Typical case of `Field` is the `RealField` which works on doubles. And typical case of `Space` is a `VectorSpace`.
+- [Space](https://mathworld.wolfram.com/VectorSpace.html) defines addition, its neutral element (i.e. 0) and scalar 
+multiplication;
+- [Ring](http://mathworld.wolfram.com/Ring.html) adds multiplication and its neutral element (i.e. 1);
+- [Field](http://mathworld.wolfram.com/Field.html) adds division operation.
 
-In some cases algebra context could hold additional operation like `exp` or `sin`, in this case it inherits appropriate
-interface. Also a context could have an operation which produces an element outside of its context. For example
-`Matrix` `dot` operation produces a matrix with new dimensions which can be incompatible with initial matrix in
-terms of linear operations.
+A typical implementation of `Field<T>` is the `RealField` which works on doubles, and `VectorSpace` for `Space<T>`.
 
-## Algebra element
+In some cases algebra context can hold additional operations like `exp` or `sin`, and then it inherits appropriate
+interface. Also, contexts may have operations, which produce elements outside of the context. For example, `Matrix.dot` 
+operation produces a matrix with new dimensions, which can be incompatible with initial matrix in terms of linear 
+operations.
 
-In order to achieve more familiar behavior (where you apply operations directly to mathematical objects), without involving contexts
-`kmath` introduces special type objects called `MathElement`. A `MathElement` is basically some object coupled to
+## Algebraic Element
+
+To achieve more familiar behavior (where you apply operations directly to mathematical objects), without involving 
+contexts KMath submits special type objects called `MathElement`. A `MathElement` is basically some object coupled to
 a mathematical context. For example `Complex` is the pair of real numbers representing real and imaginary parts,
-but it also holds reference to the `ComplexField` singleton which allows to perform direct operations on `Complex`
+but it also holds reference to the `ComplexField` singleton, which allows performing direct operations on `Complex`
 numbers without explicit involving the context like:
 
 ```kotlin
-    val c1 = Complex(1.0, 1.0)
-    val c2 = Complex(1.0, -1.0)
-    val c3 = c1 + c2 + 3.0.toComplex()
-    //or with field notation:
-    val c4 = ComplexField.run{c1 + i - 2.0}
+import scientifik.kmath.operations.*
+
+// Using elements
+val c1 = Complex(1.0, 1.0)
+val c2 = Complex(1.0, -1.0)
+val c3 = c1 + c2 + 3.0.toComplex()
+
+// Using context
+val c4 = ComplexField { c1 + i - 2.0 }
 ```
 
 Both notations have their pros and cons.
 
-The hierarchy for algebra elements follows the hierarchy for the corresponding algebra.
+The hierarchy for algebraic elements follows the hierarchy for the corresponding algebraic structures.
 
-**MathElement** <- **SpaceElement** <- **RingElement** <- **FieldElement**
+**MathElement** ← **SpaceElement** ← **RingElement** ← **FieldElement**
 
-**MathElement** is the generic common ancestor of the class with context.
+`MathElement<C>` is the generic common ancestor of the class with context.
 
-One important distinction between algebra elements and algebra contexts is that algebra element has three type parameters:
+One major distinction between algebraic elements and algebraic contexts is that elements have three type 
+parameters:
 
-1. The type of elements, field operates on.
-2. The self-type of the element returned from operation (must be algebra element).
+1. The type of elements, the field operates on.
+2. The self-type of the element returned from operation (which has to be an algebraic element).
 3. The type of the algebra over first type-parameter.
 
-The middle type is needed in case algebra members do not store context. For example, it is not possible to add
-a context to regular `Double`. The element performs automatic conversions from context types and back.
-One should used context operations in all important places. The performance of element operations is not guaranteed.
+The middle type is needed for of algebra members do not store context. For example, it is impossible to add a context 
+to regular `Double`. The element performs automatic conversions from context types and back. One should use context 
+operations in all performance-critical places. The performance of element operations is not guaranteed.
 
-## Spaces and fields
+## Spaces and Fields
 
-An obvious first choice of mathematical objects to implement in a context-oriented style are algebraic elements like spaces,
-rings and fields. Those are located in the `scientifik.kmath.operations.Algebra.kt` file. Alongside common contexts, the file includes definitions for algebra elements like `FieldElement`. A `FieldElement` object
-stores a reference to the `Field` which contains additive and multiplicative operations, meaning
-it has one fixed context attached and does not require explicit external context. So those `MathElements` can be operated without context:
+KMath submits both contexts and elements for builtin algebraic structures:
 
 ```kotlin
+import scientifik.kmath.operations.*
+
 val c1 = Complex(1.0, 2.0)
 val c2 = ComplexField.i
+
 val c3 = c1 + c2
+// or
+val c3 = ComplexField { c1 + c2 }
 ```
 
-`ComplexField` also features special operations to mix complex and real numbers, for example:
+Also, `ComplexField` features special operations to mix complex and real numbers, for example:
 
 ```kotlin
+import scientifik.kmath.operations.*
+
 val c1 = Complex(1.0, 2.0)
-val c2 = ComplexField.run{ c1 - 1.0} // Returns: [re:0.0, im: 2.0]
-val c3 = ComplexField.run{ c1 - i*2.0}
+val c2 = ComplexField { c1 - 1.0 } // Returns: Complex(re=0.0, im=2.0)
+val c3 = ComplexField { c1 - i * 2.0 }
 ```
 
-**Note**: In theory it is possible to add behaviors directly to the context, but currently kotlin syntax does not support
-that. Watch [KT-10468](https://youtrack.jetbrains.com/issue/KT-10468) and [KEEP-176](https://github.com/Kotlin/KEEP/pull/176) for updates.
+**Note**: In theory it is possible to add behaviors directly to the context, but as for now Kotlin does not support 
+that. Watch [KT-10468](https://youtrack.jetbrains.com/issue/KT-10468) and 
+[KEEP-176](https://github.com/Kotlin/KEEP/pull/176) for updates.
 
 ## Nested fields
 
-Contexts allow one to build more complex structures. For example, it is possible to create a `Matrix` from complex elements like so:
+Contexts allow one to build more complex structures. For example, it is possible to create a `Matrix` from complex 
+elements like so:
 
 ```kotlin
-val element = NDElement.complex(shape = intArrayOf(2,2)){ index: IntArray ->
+val element = NDElement.complex(shape = intArrayOf(2, 2)) { index: IntArray ->
     Complex(index[0].toDouble() - index[1].toDouble(), index[0].toDouble() + index[1].toDouble())
 }
 ```
 
-The `element` in this example is a member of the `Field` of 2-d structures, each element of which is a member of its own
-`ComplexField`. The important thing is one does not need to create a special n-d class to hold complex
+The `element` in this example is a member of the `Field` of 2D structures, each element of which is a member of its own
+`ComplexField`. It is important one does not need to create a special n-d class to hold complex
 numbers and implement operations on it, one just needs to provide a field for its elements.
 
 **Note**: Fields themselves do not solve the problem of JVM boxing, but it is possible to solve with special contexts like

doc/buffers.md

@@ -1,4 +1,5 @@
 # Buffers
+
 Buffer is one of main building blocks of kmath. It is a basic interface allowing random-access read and write (with `MutableBuffer`).
 There are different types of buffers:
 
@@ -12,4 +13,5 @@ Some kmath features require a `BufferFactory` class to operate properly. A gener
 buffer for given reified type (for types with custom memory buffer it still better to use their own `MemoryBuffer.create()` factory).
 
 ## Buffer performance
+
 One should avoid using default boxing buffer wherever it is possible. Try to use primitive buffers or memory buffers instead  

doc/codestyle.md

@@ -0,0 +1,34 @@
+# Coding Conventions
+
+KMath code follows general [Kotlin conventions](https://kotlinlang.org/docs/reference/coding-conventions.html), but 
+with a number of small changes and clarifications.
+
+## Utility Class Naming
+
+Filename should coincide with a name of one of the classes contained in the file or start with small letter and 
+describe its contents.
+
+The code convention [here](https://kotlinlang.org/docs/reference/coding-conventions.html#source-file-names) says that 
+file names should start with a capital letter even if file does not contain classes. Yet starting utility classes and 
+aggregators with a small letter seems to be a good way to visually separate those files.
+
+This convention could be changed in future in a non-breaking way.
+
+## Private Variable Naming
+
+Private variables' names may start with underscore `_` for of the private mutable variable is shadowed by the public 
+read-only value with the same meaning.
+
+This rule does not permit underscores in names, but it is sometimes useful to "underscore" the fact that public and 
+private versions draw up the same entity. It is allowed only for private variables.
+
+This convention could be changed in future in a non-breaking way.
+
+## Functions and Properties One-liners
+
+Use one-liners when they occupy single code window line both for functions and properties with getters like 
+`val b: String get() = "fff"`. The same should be performed with multiline expressions when they could be 
+cleanly separated.
+
+There is no universal consensus whenever use `fun a() = ...` or `fun a() { return ... }`. Yet from reader outlook 
+one-lines seem to better show that the property or function is easily calculated.

doc/linear.md

@@ -1,6 +1,6 @@
 ## Basic linear algebra layout
 
-Kmath support for linear algebra organized in a context-oriented way. Meaning that operations are in most cases declared 
+KMath support for linear algebra organized in a context-oriented way. Meaning that operations are in most cases declared 
 in context classes, and are not the members of classes that store data. This allows more flexible approach to maintain multiple 
 back-ends. The new operations added as extensions to contexts instead of being member functions of data structures.
 

doc/nd-structure.md

@@ -1,4 +1,4 @@
-# Nd-structure generation and operations
+# ND-structure generation and operations
 
 **TODO**
 

docs/codestyle.md

@@ -1,22 +0,0 @@
-# Local coding conventions
-
-Kmath and other `scientifik` projects use general [kotlin code conventions](https://kotlinlang.org/docs/reference/coding-conventions.html), but with a number of small changes and clarifications.
-
-## Utility class names
-File name should coincide with a name of one of the classes contained in the file or start with small letter and describe its contents.
-
-The code convention [here](https://kotlinlang.org/docs/reference/coding-conventions.html#source-file-names) says that file names should start with capital letter even if file does not contain classes. Yet starting utility classes and aggregators with a small letter seems to be a good way to clearly visually separate those files.
-
-This convention could be changed in future in a non-breaking way.
-
-## Private variable names
-Private variable names could start with underscore `_` in case the private mutable variable is shadowed by the public read-only value with the same meaning.
-
-Code convention do not permit underscores in names, but is is sometimes useful to "underscore" the fact that public and private versions define the same entity. It is allowed only for private variables.
-
-This convention could be changed in future in a non-breaking way.
-
-## Functions and properties one-liners
-Use one-liners when they occupy single code window line both for functions and properties with getters like `val b: String get() = "fff"`. The same should be done with multiline expressions when they could be cleanly separated.
-
-There is not general consensus whenever use `fun a() = {}` or `fun a(){return}`. Yet from reader perspective one-lines seem to better show that the property or function is easily calculated.

examples/build.gradle.kts

@@ -56,9 +56,16 @@ benchmark {
     }
 }
 
+kotlin.sourceSets.all {
+    with(languageSettings) {
+        useExperimentalAnnotation("kotlin.contracts.ExperimentalContracts")
+        useExperimentalAnnotation("kotlin.ExperimentalUnsignedTypes")
+    }
+}
 
 tasks.withType<KotlinCompile> {
     kotlinOptions {
         jvmTarget = Scientifik.JVM_TARGET.toString()
+        freeCompilerArgs = freeCompilerArgs + "-Xopt-in=kotlin.RequiresOptIn"
     }
 }

examples/src/benchmarks/kotlin/scientifik/kmath/structures/NDFieldBenchmark.kt

@@ -4,46 +4,38 @@ import org.openjdk.jmh.annotations.Benchmark
 import org.openjdk.jmh.annotations.Scope
 import org.openjdk.jmh.annotations.State
 import scientifik.kmath.operations.RealField
+import scientifik.kmath.operations.invoke
 
 @State(Scope.Benchmark)
 class NDFieldBenchmark {
-
     @Benchmark
     fun autoFieldAdd() {
-        bufferedField.run {
+        bufferedField {
             var res: NDBuffer<Double> = one
-            repeat(n) {
-                res += one
-            }
+            repeat(n) { res += one }
         }
     }
 
     @Benchmark
     fun autoElementAdd() {
         var res = genericField.one
-        repeat(n) {
-            res += 1.0
-        }
+        repeat(n) { res += 1.0 }
     }
 
     @Benchmark
     fun specializedFieldAdd() {
-        specializedField.run {
+        specializedField {
             var res: NDBuffer<Double> = one
-            repeat(n) {
-                res += 1.0
-            }
+            repeat(n) { res += 1.0 }
         }
     }
 
 
     @Benchmark
     fun boxingFieldAdd() {
-        genericField.run {
+        genericField {
             var res: NDBuffer<Double> = one
-            repeat(n) {
-                res += one
-            }
+            repeat(n) { res += one }
         }
     }
 

examples/src/benchmarks/kotlin/scientifik/kmath/structures/ViktorBenchmark.kt

@@ -5,23 +5,22 @@ import org.openjdk.jmh.annotations.Benchmark
 import org.openjdk.jmh.annotations.Scope
 import org.openjdk.jmh.annotations.State
 import scientifik.kmath.operations.RealField
+import scientifik.kmath.operations.invoke
 import scientifik.kmath.viktor.ViktorNDField
 
-
 @State(Scope.Benchmark)
 class ViktorBenchmark {
     final val dim = 1000
     final val n = 100
 
     // automatically build context most suited for given type.
-    final val autoField = NDField.auto(RealField, dim, dim)
-    final val realField = NDField.real(dim, dim)
-
-    final val viktorField = ViktorNDField(intArrayOf(dim, dim))
+    final val autoField: BufferedNDField<Double, RealField> = NDField.auto(RealField, dim, dim)
+    final val realField: RealNDField = NDField.real(dim, dim)
+    final val viktorField: ViktorNDField = ViktorNDField(intArrayOf(dim, dim))
 
     @Benchmark
     fun automaticFieldAddition() {
-        autoField.run {
+        autoField {
             var res = one
             repeat(n) { res += one }
         }
@@ -29,7 +28,7 @@ class ViktorBenchmark {
 
     @Benchmark
     fun viktorFieldAddition() {
-        viktorField.run {
+        viktorField {
             var res = one
             repeat(n) { res += one }
         }
@@ -44,7 +43,7 @@ class ViktorBenchmark {
 
     @Benchmark
     fun realdFieldLog() {
-        realField.run {
+        realField {
             val fortyTwo = produce { 42.0 }
             var res = one
             repeat(n) { res = ln(fortyTwo) }

examples/src/benchmarks/kotlin/scientifik/kmath/utils/utils.kt

@@ -1,8 +1,11 @@
 package scientifik.kmath.utils
 
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 import kotlin.system.measureTimeMillis
 
 internal inline fun measureAndPrint(title: String, block: () -> Unit) {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
     val time = measureTimeMillis(block)
     println("$title completed in $time millis")
 }

examples/src/main/kotlin/scientifik/kmath/linear/LinearAlgebraBenchmark.kt

@@ -5,6 +5,7 @@ import scientifik.kmath.commons.linear.CMMatrixContext
 import scientifik.kmath.commons.linear.inverse
 import scientifik.kmath.commons.linear.toCM
 import scientifik.kmath.operations.RealField
+import scientifik.kmath.operations.invoke
 import scientifik.kmath.structures.Matrix
 import kotlin.contracts.ExperimentalContracts
 import kotlin.random.Random
@@ -21,29 +22,18 @@ fun main() {
 
     val n = 5000 // iterations
 
-    MatrixContext.real.run {
-
-        repeat(50) {
-            val res = inverse(matrix)
-        }
-
-        val inverseTime = measureTimeMillis {
-            repeat(n) {
-                val res = inverse(matrix)
-            }
-        }
-
+    MatrixContext.real {
+        repeat(50) { val res = inverse(matrix) }
+        val inverseTime = measureTimeMillis { repeat(n) { val res = inverse(matrix) } }
         println("[kmath] Inversion of $n matrices $dim x $dim finished in $inverseTime millis")
     }
 
     //commons-math
 
     val commonsTime = measureTimeMillis {
-        CMMatrixContext.run {
+        CMMatrixContext {
             val cm = matrix.toCM()             //avoid overhead on conversion
-            repeat(n) {
-                val res = inverse(cm)
-            }
+            repeat(n) { val res = inverse(cm) }
         }
     }
 
@@ -53,7 +43,7 @@ fun main() {
     //koma-ejml
 
     val komaTime = measureTimeMillis {
-        KomaMatrixContext(EJMLMatrixFactory(), RealField).run {
+        (KomaMatrixContext(EJMLMatrixFactory(), RealField)) {
             val km = matrix.toKoma()      //avoid overhead on conversion
             repeat(n) {
                 val res = inverse(km)

examples/src/main/kotlin/scientifik/kmath/linear/MultiplicationBenchmark.kt

@@ -4,6 +4,7 @@ import koma.matrix.ejml.EJMLMatrixFactory
 import scientifik.kmath.commons.linear.CMMatrixContext
 import scientifik.kmath.commons.linear.toCM
 import scientifik.kmath.operations.RealField
+import scientifik.kmath.operations.invoke
 import scientifik.kmath.structures.Matrix
 import kotlin.random.Random
 import kotlin.system.measureTimeMillis
@@ -18,7 +19,7 @@ fun main() {
 //    //warmup
 //    matrix1 dot matrix2
 
-    CMMatrixContext.run {
+    CMMatrixContext {
         val cmMatrix1 = matrix1.toCM()
         val cmMatrix2 = matrix2.toCM()
 
@@ -29,8 +30,7 @@ fun main() {
         println("CM implementation time: $cmTime")
     }
 
-
-    KomaMatrixContext(EJMLMatrixFactory(), RealField).run {
+    (KomaMatrixContext(EJMLMatrixFactory(), RealField)) {
         val komaMatrix1 = matrix1.toKoma()
         val komaMatrix2 = matrix2.toKoma()
 

examples/src/main/kotlin/scientifik/kmath/operations/ComplexDemo.kt

@@ -9,13 +9,11 @@ fun main() {
         Complex(index[0].toDouble() - index[1].toDouble(), index[0].toDouble() + index[1].toDouble())
     }
 
-
-    val compute = NDField.complex(8).run {
+    val compute = (NDField.complex(8)) {
         val a = produce { (it) -> i * it - it.toDouble() }
         val b = 3
         val c = Complex(1.0, 1.0)
 
         (a pow b) + c
     }
-
 }

examples/src/main/kotlin/scientifik/kmath/structures/ComplexND.kt

@@ -13,9 +13,8 @@ fun main() {
     val realField = NDField.real(dim, dim)
     val complexField = NDField.complex(dim, dim)
 
-
     val realTime = measureTimeMillis {
-        realField.run {
+        realField {
             var res: NDBuffer<Double> = one
             repeat(n) {
                 res += 1.0
@@ -26,18 +25,15 @@ fun main() {
     println("Real addition completed in $realTime millis")
 
     val complexTime = measureTimeMillis {
-        complexField.run {
+        complexField {
             var res: NDBuffer<Complex> = one
-            repeat(n) {
-                res += 1.0
-            }
+            repeat(n) { res += 1.0 }
         }
     }
 
     println("Complex addition completed in $complexTime millis")
 }
 
-
 fun complexExample() {
     //Create a context for 2-d structure with complex values
     ComplexField {
@@ -46,10 +42,7 @@ fun complexExample() {
             val x = one * 2.5
             operator fun Number.plus(other: Complex) = Complex(this.toDouble() + other.re, other.im)
             //a structure generator specific to this context
-            val matrix = produce { (k, l) ->
-                k + l * i
-            }
-
+            val matrix = produce { (k, l) -> k + l * i }
             //Perform sum
             val sum = matrix + x + 1.0
 

examples/src/main/kotlin/scientifik/kmath/structures/NDField.kt

@@ -2,14 +2,18 @@ package scientifik.kmath.structures
 
 import kotlinx.coroutines.GlobalScope
 import scientifik.kmath.operations.RealField
+import scientifik.kmath.operations.invoke
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 import kotlin.system.measureTimeMillis
 
 internal inline fun measureAndPrint(title: String, block: () -> Unit) {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
     val time = measureTimeMillis(block)
     println("$title completed in $time millis")
 }
 
-
 fun main() {
     val dim = 1000
     val n = 1000
@@ -22,27 +26,21 @@ fun main() {
     val genericField = NDField.boxing(RealField, dim, dim)
 
     measureAndPrint("Automatic field addition") {
-        autoField.run {
+        autoField {
             var res: NDBuffer<Double> = one
-            repeat(n) {
-                res += number(1.0)
-            }
+            repeat(n) { res += number(1.0) }
         }
     }
 
     measureAndPrint("Element addition") {
         var res = genericField.one
-        repeat(n) {
-            res += 1.0
-        }
+        repeat(n) { res += 1.0 }
     }
 
     measureAndPrint("Specialized addition") {
-        specializedField.run {
+        specializedField {
             var res: NDBuffer<Double> = one
-            repeat(n) {
-                res += 1.0
-            }
+            repeat(n) { res += 1.0 }
         }
     }
 
@@ -60,12 +58,11 @@ fun main() {
 
     measureAndPrint("Generic addition") {
         //genericField.run(action)
-        genericField.run {
+        genericField {
             var res: NDBuffer<Double> = one
             repeat(n) {
-                res += one // con't avoid using `one` due to resolution ambiguity
+                res += one // couldn't avoid using `one` due to resolution ambiguity }
             }
         }
     }
-
 }

examples/src/main/kotlin/scientifik/kmath/structures/typeSafeDimensions.kt

@@ -23,13 +23,10 @@ fun DMatrixContext<Double, RealField>.custom() {
     val m1 = produce<D2, D5> { i, j -> (i + j).toDouble() }
     val m2 = produce<D5, D2> { i, j -> (i - j).toDouble() }
     val m3 = produce<D2, D2> { i, j -> (i - j).toDouble() }
-
     (m1 dot m2) + m3
 }
 
-fun main() {
-    DMatrixContext.real.run {
+fun main(): Unit = with(DMatrixContext.real) {
     simple()
     custom()
-    }
 }

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-6.5-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.5.1-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists

kmath-ast/README.md

@@ -1,4 +1,4 @@
-# Abstract syntax tree expression representation and operations (`kmath-ast`)
+# Abstract Syntax Tree Expression Representation and Operations (`kmath-ast`)
 
 This subproject implements the following features:
 
@@ -38,7 +38,7 @@ This subproject implements the following features:
 > ```
 >
 
-## Dynamic expression code generation with ObjectWeb ASM
+## Dynamic Expression Code Generation with ObjectWeb ASM
 
 `kmath-ast` JVM module supports runtime code generation to eliminate overhead of tree traversal. Code generator builds 
 a special implementation of `Expression<T>` with implemented `invoke` function. 
@@ -46,7 +46,7 @@ a special implementation of `Expression<T>` with implemented `invoke` function.
 For example, the following builder: 
 
 ```kotlin
-    RealField.mstInField { symbol("x") + 2 }.compile()
+RealField.mstInField { symbol("x") + 2 }.compile()
 ``` 
 
 … leads to generation of bytecode, which can be decompiled to the following Java class: 
@@ -75,7 +75,7 @@ public final class AsmCompiledExpression_1073786867_0 implements Expression<Doub
 
 ### Example Usage
 
-This API is an extension to MST and MstExpression, so you may optimize as both of them: 
+This API extends MST and MstExpression, so you may optimize as both of them: 
 
 ```kotlin
 RealField.mstInField { symbol("x") + 2 }.compile()

kmath-ast/build.gradle.kts

@@ -1,37 +1,20 @@
-plugins {
-    id("scientifik.mpp")
-}
-
-repositories {
-    maven("https://dl.bintray.com/hotkeytlt/maven")
-}
+plugins { id("scientifik.mpp") }
 
 kotlin.sourceSets {
-//    all {
-//       languageSettings.apply{
-//            enableLanguageFeature("NewInference")
-//       }
-//    }
+    all { languageSettings.useExperimentalAnnotation("kotlin.contracts.ExperimentalContracts") }
+
     commonMain {
         dependencies {
             api(project(":kmath-core"))
-            implementation("com.github.h0tk3y.betterParse:better-parse-multiplatform:0.4.0-alpha-3")
-            implementation("com.github.h0tk3y.betterParse:better-parse-multiplatform-metadata:0.4.0-alpha-3")
+            implementation("com.github.h0tk3y.betterParse:better-parse:0.4.0")
         }
     }
 
     jvmMain {
         dependencies {
-            implementation("com.github.h0tk3y.betterParse:better-parse-jvm:0.4.0-alpha-3")
             implementation("org.ow2.asm:asm:8.0.1")
             implementation("org.ow2.asm:asm-commons:8.0.1")
             implementation(kotlin("reflect"))
         }
     }
-
-    jsMain {
-        dependencies {
-            implementation("com.github.h0tk3y.betterParse:better-parse-js:0.4.0-alpha-3")
-        }
-    }
 }

kmath-ast/reference/ArithmeticsEvaluator.g4

@@ -0,0 +1,59 @@
+grammar ArithmeticsEvaluator;
+
+fragment DIGIT: '0'..'9';
+fragment LETTER: 'a'..'z';
+fragment CAPITAL_LETTER: 'A'..'Z';
+fragment UNDERSCORE: '_';
+
+ID: (LETTER | UNDERSCORE | CAPITAL_LETTER) (LETTER | UNDERSCORE | DIGIT | CAPITAL_LETTER)*;
+NUM: (DIGIT | '.')+ ([eE] [-+]? DIGIT+)?;
+MUL: '*';
+DIV: '/';
+PLUS: '+';
+MINUS: '-';
+POW: '^';
+COMMA: ',';
+LPAR: '(';
+RPAR: ')';
+WS: [ \n\t\r]+ -> skip;
+
+num
+    : NUM
+    ;
+
+singular
+    : ID
+    ;
+
+unaryFunction
+    : ID LPAR subSumChain RPAR
+    ;
+
+binaryFunction
+    : ID LPAR subSumChain COMMA subSumChain RPAR
+    ;
+
+term
+    : num
+    | singular
+    | unaryFunction
+    | binaryFunction
+    | MINUS term
+    | LPAR subSumChain RPAR
+    ;
+
+powChain
+    : term (POW term)*
+    ;
+
+divMulChain
+    : powChain ((DIV | MUL) powChain)*
+    ;
+
+subSumChain
+    : divMulChain ((PLUS | MINUS) divMulChain)*
+    ;
+
+rootParser
+    : subSumChain EOF
+    ;

kmath-ast/src/commonMain/kotlin/scientifik/kmath/ast/MST.kt

@@ -5,63 +5,83 @@ import scientifik.kmath.operations.NumericAlgebra
 import scientifik.kmath.operations.RealField
 
 /**
- * A Mathematical Syntax Tree node for mathematical expressions
+ * A Mathematical Syntax Tree node for mathematical expressions.
  */
 sealed class MST {
-
     /**
-     * A node containing unparsed string
+     * A node containing raw string.
+     *
+     * @property value the value of this node.
      */
     data class Symbolic(val value: String) : MST()
 
     /**
-     * A node containing a number
+     * A node containing a numeric value or scalar.
+     *
+     * @property value the value of this number.
      */
     data class Numeric(val value: Number) : MST()
 
     /**
-     * A node containing an unary operation
+     * A node containing an unary operation.
+     *
+     * @property operation the identifier of operation.
+     * @property value the argument of this operation.
      */
     data class Unary(val operation: String, val value: MST) : MST() {
-        companion object {
-            const val ABS_OPERATION = "abs"
-            //TODO add operations
-        }
+        companion object
     }
 
     /**
-     * A node containing binary operation
+     * A node containing binary operation.
+     *
+     * @property operation the identifier operation.
+     * @property left the left operand.
+     * @property right the right operand.
      */
     data class Binary(val operation: String, val left: MST, val right: MST) : MST() {
         companion object
     }
 }
 
-//TODO add a function with positional arguments
+// TODO add a function with named arguments
 
-//TODO add a function with named arguments
-
-fun <T> Algebra<T>.evaluate(node: MST): T {
-    return when (node) {
+/**
+ * Interprets the [MST] node with this [Algebra].
+ *
+ * @receiver the algebra that provides operations.
+ * @param node the node to evaluate.
+ * @return the value of expression.
+ */
+fun <T> Algebra<T>.evaluate(node: MST): T = when (node) {
     is MST.Numeric -> (this as? NumericAlgebra<T>)?.number(node.value)
         ?: error("Numeric nodes are not supported by $this")
     is MST.Symbolic -> symbol(node.value)
     is MST.Unary -> unaryOperation(node.operation, evaluate(node.value))
     is MST.Binary -> when {
         this !is NumericAlgebra -> binaryOperation(node.operation, evaluate(node.left), evaluate(node.right))
+
         node.left is MST.Numeric && node.right is MST.Numeric -> {
             val number = RealField.binaryOperation(
                 node.operation,
                 node.left.value.toDouble(),
                 node.right.value.toDouble()
             )
+
             number(number)
         }
+
         node.left is MST.Numeric -> leftSideNumberOperation(node.operation, node.left.value, evaluate(node.right))
         node.right is MST.Numeric -> rightSideNumberOperation(node.operation, evaluate(node.left), node.right.value)
         else -> binaryOperation(node.operation, evaluate(node.left), evaluate(node.right))
     }
-    }
 }
 
-fun <T> MST.compile(algebra: Algebra<T>): T = algebra.evaluate(this)
+/**
+ * Interprets the [MST] node with this [Algebra].
+ *
+ * @receiver the node to evaluate.
+ * @param algebra the algebra that provides operations.
+ * @return the value of expression.
+ */
+fun <T> MST.interpret(algebra: Algebra<T>): T = algebra.evaluate(this)

kmath-ast/src/commonMain/kotlin/scientifik/kmath/ast/MstAlgebra.kt

@@ -2,6 +2,9 @@ package scientifik.kmath.ast
 
 import scientifik.kmath.operations.*
 
+/**
+ * [Algebra] over [MST] nodes.
+ */
 object MstAlgebra : NumericAlgebra<MST> {
     override fun number(value: Number): MST = MST.Numeric(value)
 
@@ -14,17 +17,16 @@ object MstAlgebra : NumericAlgebra<MST> {
         MST.Binary(operation, left, right)
 }
 
+/**
+ * [Space] over [MST] nodes.
+ */
 object MstSpace : Space<MST>, NumericAlgebra<MST> {
     override val zero: MST = number(0.0)
 
     override fun number(value: Number): MST = MstAlgebra.number(value)
     override fun symbol(value: String): MST = MstAlgebra.symbol(value)
-
-    override fun add(a: MST, b: MST): MST =
-        binaryOperation(SpaceOperations.PLUS_OPERATION, a, b)
-
-    override fun multiply(a: MST, k: Number): MST =
-        binaryOperation(RingOperations.TIMES_OPERATION, a, number(k))
+    override fun add(a: MST, b: MST): MST = binaryOperation(SpaceOperations.PLUS_OPERATION, a, b)
+    override fun multiply(a: MST, k: Number): MST = binaryOperation(RingOperations.TIMES_OPERATION, a, number(k))
 
     override fun binaryOperation(operation: String, left: MST, right: MST): MST =
         MstAlgebra.binaryOperation(operation, left, right)
@@ -32,41 +34,69 @@ object MstSpace : Space<MST>, NumericAlgebra<MST> {
     override fun unaryOperation(operation: String, arg: MST): MST = MstAlgebra.unaryOperation(operation, arg)
 }
 
+/**
+ * [Ring] over [MST] nodes.
+ */
 object MstRing : Ring<MST>, NumericAlgebra<MST> {
     override val zero: MST = number(0.0)
     override val one: MST = number(1.0)
 
-    override fun number(value: Number): MST = MstAlgebra.number(value)
-    override fun symbol(value: String): MST = MstAlgebra.symbol(value)
-    override fun add(a: MST, b: MST): MST = binaryOperation(SpaceOperations.PLUS_OPERATION, a, b)
+    override fun number(value: Number): MST = MstSpace.number(value)
+    override fun symbol(value: String): MST = MstSpace.symbol(value)
+    override fun add(a: MST, b: MST): MST = MstSpace.add(a, b)
 
-    override fun multiply(a: MST, k: Number): MST =
-        binaryOperation(RingOperations.TIMES_OPERATION, a, MstSpace.number(k))
+    override fun multiply(a: MST, k: Number): MST = MstSpace.multiply(a, k)
 
     override fun multiply(a: MST, b: MST): MST = binaryOperation(RingOperations.TIMES_OPERATION, a, b)
 
     override fun binaryOperation(operation: String, left: MST, right: MST): MST =
-        MstAlgebra.binaryOperation(operation, left, right)
+        MstSpace.binaryOperation(operation, left, right)
 
     override fun unaryOperation(operation: String, arg: MST): MST = MstAlgebra.unaryOperation(operation, arg)
 }
 
+/**
+ * [Field] over [MST] nodes.
+ */
 object MstField : Field<MST> {
     override val zero: MST = number(0.0)
     override val one: MST = number(1.0)
 
-    override fun symbol(value: String): MST = MstAlgebra.symbol(value)
-    override fun number(value: Number): MST = MstAlgebra.number(value)
-    override fun add(a: MST, b: MST): MST = binaryOperation(SpaceOperations.PLUS_OPERATION, a, b)
-
-    override fun multiply(a: MST, k: Number): MST =
-        binaryOperation(RingOperations.TIMES_OPERATION, a, MstSpace.number(k))
-
-    override fun multiply(a: MST, b: MST): MST = binaryOperation(RingOperations.TIMES_OPERATION, a, b)
+    override fun symbol(value: String): MST = MstRing.symbol(value)
+    override fun number(value: Number): MST = MstRing.number(value)
+    override fun add(a: MST, b: MST): MST = MstRing.add(a, b)
+    override fun multiply(a: MST, k: Number): MST = MstRing.multiply(a, k)
+    override fun multiply(a: MST, b: MST): MST = MstRing.multiply(a, b)
     override fun divide(a: MST, b: MST): MST = binaryOperation(FieldOperations.DIV_OPERATION, a, b)
 
     override fun binaryOperation(operation: String, left: MST, right: MST): MST =
-        MstAlgebra.binaryOperation(operation, left, right)
+        MstRing.binaryOperation(operation, left, right)
 
-    override fun unaryOperation(operation: String, arg: MST): MST = MstAlgebra.unaryOperation(operation, arg)
+    override fun unaryOperation(operation: String, arg: MST): MST = MstRing.unaryOperation(operation, arg)
+}
+
+/**
+ * [ExtendedField] over [MST] nodes.
+ */
+object MstExtendedField : ExtendedField<MST> {
+    override val zero: MST = number(0.0)
+    override val one: MST = number(1.0)
+
+    override fun sin(arg: MST): MST = unaryOperation(TrigonometricOperations.SIN_OPERATION, arg)
+    override fun cos(arg: MST): MST = unaryOperation(TrigonometricOperations.COS_OPERATION, arg)
+    override fun asin(arg: MST): MST = unaryOperation(TrigonometricOperations.ASIN_OPERATION, arg)
+    override fun acos(arg: MST): MST = unaryOperation(TrigonometricOperations.ACOS_OPERATION, arg)
+    override fun atan(arg: MST): MST = unaryOperation(TrigonometricOperations.ATAN_OPERATION, arg)
+    override fun add(a: MST, b: MST): MST = MstField.add(a, b)
+    override fun multiply(a: MST, k: Number): MST = MstField.multiply(a, k)
+    override fun multiply(a: MST, b: MST): MST = MstField.multiply(a, b)
+    override fun divide(a: MST, b: MST): MST = MstField.divide(a, b)
+    override fun power(arg: MST, pow: Number): MST = binaryOperation(PowerOperations.POW_OPERATION, arg, number(pow))
+    override fun exp(arg: MST): MST = unaryOperation(ExponentialOperations.EXP_OPERATION, arg)
+    override fun ln(arg: MST): MST = unaryOperation(ExponentialOperations.LN_OPERATION, arg)
+
+    override fun binaryOperation(operation: String, left: MST, right: MST): MST =
+        MstField.binaryOperation(operation, left, right)
+
+    override fun unaryOperation(operation: String, arg: MST): MST = MstField.unaryOperation(operation, arg)
 }

kmath-ast/src/commonMain/kotlin/scientifik/kmath/ast/MstExpression.kt

@@ -1,19 +1,19 @@
 package scientifik.kmath.ast
 
-import scientifik.kmath.expressions.Expression
-import scientifik.kmath.expressions.FunctionalExpressionField
-import scientifik.kmath.expressions.FunctionalExpressionRing
-import scientifik.kmath.expressions.FunctionalExpressionSpace
+import scientifik.kmath.expressions.*
 import scientifik.kmath.operations.*
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 
 /**
- * The expression evaluates MST on-flight. Should be much faster than functional expression, but slower than ASM-generated expressions.
+ * The expression evaluates MST on-flight. Should be much faster than functional expression, but slower than
+ * ASM-generated expressions.
+ *
+ * @property algebra the algebra that provides operations.
+ * @property mst the [MST] node.
  */
 class MstExpression<T>(val algebra: Algebra<T>, val mst: MST) : Expression<T> {
-
-    /**
-     * Substitute algebra raw value
-     */
     private inner class InnerAlgebra(val arguments: Map<String, T>) : NumericAlgebra<T> {
         override fun symbol(value: String): T = arguments[value] ?: algebra.symbol(value)
         override fun unaryOperation(operation: String, arg: T): T = algebra.unaryOperation(operation, arg)
@@ -27,29 +27,77 @@ class MstExpression<T>(val algebra: Algebra<T>, val mst: MST) : Expression<T> {
             error("Numeric nodes are not supported by $this")
     }
 
-    override fun invoke(arguments: Map<String, T>): T = InnerAlgebra(arguments).evaluate(mst)
+    override operator fun invoke(arguments: Map<String, T>): T = InnerAlgebra(arguments).evaluate(mst)
 }
 
-
+/**
+ * Builds [MstExpression] over [Algebra].
+ */
 inline fun <reified T : Any, A : Algebra<T>, E : Algebra<MST>> A.mst(
     mstAlgebra: E,
     block: E.() -> MST
 ): MstExpression<T> = MstExpression(this, mstAlgebra.block())
 
-inline fun <reified T : Any> Space<T>.mstInSpace(block: MstSpace.() -> MST): MstExpression<T> =
-    MstExpression(this, MstSpace.block())
+/**
+ * Builds [MstExpression] over [Space].
+ */
+inline fun <reified T : Any> Space<T>.mstInSpace(block: MstSpace.() -> MST): MstExpression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return MstExpression(this, MstSpace.block())
+}
 
-inline fun <reified T : Any> Ring<T>.mstInRing(block: MstRing.() -> MST): MstExpression<T> =
-    MstExpression(this, MstRing.block())
+/**
+ * Builds [MstExpression] over [Ring].
+ */
+inline fun <reified T : Any> Ring<T>.mstInRing(block: MstRing.() -> MST): MstExpression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return MstExpression(this, MstRing.block())
+}
 
-inline fun <reified T : Any> Field<T>.mstInField(block: MstField.() -> MST): MstExpression<T> =
-    MstExpression(this, MstField.block())
+/**
+ * Builds [MstExpression] over [Field].
+ */
+inline fun <reified T : Any> Field<T>.mstInField(block: MstField.() -> MST): MstExpression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return MstExpression(this, MstField.block())
+}
 
-inline fun <reified T : Any, A : Space<T>> FunctionalExpressionSpace<T, A>.mstInSpace(block: MstSpace.() -> MST): MstExpression<T> =
-    algebra.mstInSpace(block)
+/**
+ * Builds [MstExpression] over [ExtendedField].
+ */
+inline fun <reified T : Any> Field<T>.mstInExtendedField(block: MstExtendedField.() -> MST): MstExpression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return MstExpression(this, MstExtendedField.block())
+}
 
-inline fun <reified T : Any, A : Ring<T>> FunctionalExpressionRing<T, A>.mstInRing(block: MstRing.() -> MST): MstExpression<T> =
-    algebra.mstInRing(block)
+/**
+ * Builds [MstExpression] over [FunctionalExpressionSpace].
+ */
+inline fun <reified T : Any, A : Space<T>> FunctionalExpressionSpace<T, A>.mstInSpace(block: MstSpace.() -> MST): MstExpression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return algebra.mstInSpace(block)
+}
 
-inline fun <reified T : Any, A : Field<T>> FunctionalExpressionField<T, A>.mstInField(block: MstField.() -> MST): MstExpression<T> =
-    algebra.mstInField(block)
+/**
+ * Builds [MstExpression] over [FunctionalExpressionRing].
+ */
+inline fun <reified T : Any, A : Ring<T>> FunctionalExpressionRing<T, A>.mstInRing(block: MstRing.() -> MST): MstExpression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return algebra.mstInRing(block)
+}
+
+/**
+ * Builds [MstExpression] over [FunctionalExpressionField].
+ */
+inline fun <reified T : Any, A : Field<T>> FunctionalExpressionField<T, A>.mstInField(block: MstField.() -> MST): MstExpression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return algebra.mstInField(block)
+}
+
+/**
+ * Builds [MstExpression] over [FunctionalExpressionExtendedField].
+ */
+inline fun <reified T : Any, A : ExtendedField<T>> FunctionalExpressionExtendedField<T, A>.mstInExtendedField(block: MstExtendedField.() -> MST): MstExpression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return algebra.mstInExtendedField(block)
+}

kmath-ast/src/commonMain/kotlin/scientifik/kmath/ast/parser.kt

@@ -5,6 +5,9 @@ import com.github.h0tk3y.betterParse.grammar.Grammar
 import com.github.h0tk3y.betterParse.grammar.parseToEnd
 import com.github.h0tk3y.betterParse.grammar.parser
 import com.github.h0tk3y.betterParse.grammar.tryParseToEnd
+import com.github.h0tk3y.betterParse.lexer.Token
+import com.github.h0tk3y.betterParse.lexer.TokenMatch
+import com.github.h0tk3y.betterParse.lexer.regexToken
 import com.github.h0tk3y.betterParse.parser.ParseResult
 import com.github.h0tk3y.betterParse.parser.Parser
 import scientifik.kmath.operations.FieldOperations
@@ -13,47 +16,82 @@ import scientifik.kmath.operations.RingOperations
 import scientifik.kmath.operations.SpaceOperations
 
 /**
- * TODO move to common
+ * TODO move to core
  */
-private object ArithmeticsEvaluator : Grammar<MST>() {
-    val num by token("-?[\\d.]+(?:[eE]-?\\d+)?".toRegex())
-    val lpar by token("\\(".toRegex())
-    val rpar by token("\\)".toRegex())
-    val mul by token("\\*".toRegex())
-    val pow by token("\\^".toRegex())
-    val div by token("/".toRegex())
-    val minus by token("-".toRegex())
-    val plus by token("\\+".toRegex())
-    val ws by token("\\s+".toRegex(), ignore = true)
+object ArithmeticsEvaluator : Grammar<MST>() {
+    // TODO replace with "...".toRegex() when better-parse 0.4.1 is released
+    private val num: Token by regexToken("[\\d.]+(?:[eE][-+]?\\d+)?")
+    private val id: Token by regexToken("[a-z_A-Z][\\da-z_A-Z]*")
+    private val lpar: Token by regexToken("\\(")
+    private val rpar: Token by regexToken("\\)")
+    private val comma: Token by regexToken(",")
+    private val mul: Token by regexToken("\\*")
+    private val pow: Token by regexToken("\\^")
+    private val div: Token by regexToken("/")
+    private val minus: Token by regexToken("-")
+    private val plus: Token by regexToken("\\+")
+    private val ws: Token by regexToken("\\s+", ignore = true)
 
-    val number: Parser<MST> by num use { MST.Numeric(text.toDouble()) }
+    private val number: Parser<MST> by num use { MST.Numeric(text.toDouble()) }
+    private val singular: Parser<MST> by id use { MST.Symbolic(text) }
 
-    val term: Parser<MST> by number or
-            (skip(minus) and parser(this::term) map { MST.Unary(SpaceOperations.MINUS_OPERATION, it) }) or
-            (skip(lpar) and parser(this::rootParser) and skip(rpar))
+    private val unaryFunction: Parser<MST> by (id and skip(lpar) and parser(::subSumChain) and skip(rpar))
+        .map { (id, term) -> MST.Unary(id.text, term) }
 
-    val powChain by leftAssociative(term, pow) { a, _, b ->
+    private val binaryFunction: Parser<MST> by id
+        .and(skip(lpar))
+        .and(parser(::subSumChain))
+        .and(skip(comma))
+        .and(parser(::subSumChain))
+        .and(skip(rpar))
+        .map { (id, left, right) -> MST.Binary(id.text, left, right) }
+
+    private val term: Parser<MST> by number
+        .or(binaryFunction)
+        .or(unaryFunction)
+        .or(singular)
+        .or(skip(minus) and parser(::term) map { MST.Unary(SpaceOperations.MINUS_OPERATION, it) })
+        .or(skip(lpar) and parser(::subSumChain) and skip(rpar))
+
+    private val powChain: Parser<MST> by leftAssociative(term = term, operator = pow) { a, _, b ->
         MST.Binary(PowerOperations.POW_OPERATION, a, b)
     }
 
-    val divMulChain: Parser<MST> by leftAssociative(powChain, div or mul use { type }) { a, op, b ->
-        if (op == div) {
+    private val divMulChain: Parser<MST> by leftAssociative(
+        term = powChain,
+        operator = div or mul use TokenMatch::type
+    ) { a, op, b ->
+        if (op == div)
             MST.Binary(FieldOperations.DIV_OPERATION, a, b)
-        } else {
+        else
             MST.Binary(RingOperations.TIMES_OPERATION, a, b)
     }
-    }
 
-    val subSumChain: Parser<MST> by leftAssociative(divMulChain, plus or minus use { type }) { a, op, b ->
-        if (op == plus) {
+    private val subSumChain: Parser<MST> by leftAssociative(
+        term = divMulChain,
+        operator = plus or minus use TokenMatch::type
+    ) { a, op, b ->
+        if (op == plus)
             MST.Binary(SpaceOperations.PLUS_OPERATION, a, b)
-        } else {
+        else
             MST.Binary(SpaceOperations.MINUS_OPERATION, a, b)
     }
-    }
 
     override val rootParser: Parser<MST> by subSumChain
 }
 
+/**
+ * Tries to parse the string into [MST].
+ *
+ * @receiver the string to parse.
+ * @return the [MST] node.
+ */
 fun String.tryParseMath(): ParseResult<MST> = ArithmeticsEvaluator.tryParseToEnd(this)
+
+/**
+ * Parses the string into [MST].
+ *
+ * @receiver the string to parse.
+ * @return the [MST] node.
+ */
 fun String.parseMath(): MST = ArithmeticsEvaluator.parseToEnd(this)

kmath-ast/src/jvmMain/kotlin/scientifik/kmath/asm/asm.kt

@@ -8,7 +8,6 @@ import scientifik.kmath.ast.MST
 import scientifik.kmath.ast.MstExpression
 import scientifik.kmath.expressions.Expression
 import scientifik.kmath.operations.Algebra
-import scientifik.kmath.operations.NumericAlgebra
 import kotlin.reflect.KClass
 
 /**
@@ -17,7 +16,19 @@ import kotlin.reflect.KClass
 fun <T : Any> MST.compileWith(type: KClass<T>, algebra: Algebra<T>): Expression<T> {
     fun AsmBuilder<T>.visit(node: MST) {
         when (node) {
-            is MST.Symbolic -> loadVariable(node.value)
+            is MST.Symbolic -> {
+                val symbol = try {
+                    algebra.symbol(node.value)
+                } catch (ignored: Throwable) {
+                    null
+                }
+
+                if (symbol != null)
+                    loadTConstant(symbol)
+                else
+                    loadVariable(node.value)
+            }
+
             is MST.Numeric -> loadNumeric(node.value)
 
             is MST.Unary -> buildAlgebraOperationCall(

kmath-ast/src/jvmMain/kotlin/scientifik/kmath/asm/internal/AsmBuilder.kt

@@ -288,7 +288,7 @@ internal class AsmBuilder<T> internal constructor(
     /**
      * Loads a [T] constant from [constants].
      */
-    private fun loadTConstant(value: T) {
+    internal fun loadTConstant(value: T) {
         if (classOfT in INLINABLE_NUMBERS) {
             val expectedType = expectationStack.pop()
             val mustBeBoxed = expectedType.sort == Type.OBJECT
@@ -340,7 +340,7 @@ internal class AsmBuilder<T> internal constructor(
         checkcast(type)
     }
 
-    fun loadNumeric(value: Number) {
+    internal fun loadNumeric(value: Number) {
         if (expectationStack.peek() == NUMBER_TYPE) {
             loadNumberConstant(value, true)
             expectationStack.pop()

kmath-ast/src/jvmMain/kotlin/scientifik/kmath/asm/internal/codegenUtils.kt

@@ -7,6 +7,9 @@ import scientifik.kmath.ast.MST
 import scientifik.kmath.expressions.Expression
 import scientifik.kmath.operations.Algebra
 import java.lang.reflect.Method
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 import kotlin.reflect.KClass
 
 private val methodNameAdapters: Map<Pair<String, Int>, String> by lazy {
@@ -26,8 +29,10 @@ internal val KClass<*>.asm: Type
 /**
  * Returns singleton array with this value if the [predicate] is true, returns empty array otherwise.
  */
-internal inline fun <reified T> T.wrapToArrayIf(predicate: (T) -> Boolean): Array<T> =
-    if (predicate(this)) arrayOf(this) else emptyArray()
+internal inline fun <reified T> T.wrapToArrayIf(predicate: (T) -> Boolean): Array<T> {
+    contract { callsInPlace(predicate, InvocationKind.EXACTLY_ONCE) }
+    return if (predicate(this)) arrayOf(this) else emptyArray()
+}
 
 /**
  * Creates an [InstructionAdapter] from this [MethodVisitor].
@@ -37,8 +42,10 @@ private fun MethodVisitor.instructionAdapter(): InstructionAdapter = Instruction
 /**
  * Creates an [InstructionAdapter] from this [MethodVisitor] and applies [block] to it.
  */
-internal fun MethodVisitor.instructionAdapter(block: InstructionAdapter.() -> Unit): InstructionAdapter =
-    instructionAdapter().apply(block)
+internal inline fun MethodVisitor.instructionAdapter(block: InstructionAdapter.() -> Unit): InstructionAdapter {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return instructionAdapter().apply(block)
+}
 
 /**
  * Constructs a [Label], then applies it to this visitor.
@@ -64,8 +71,10 @@ internal tailrec fun buildName(mst: MST, collision: Int = 0): String {
 }
 
 @Suppress("FunctionName")
-internal inline fun ClassWriter(flags: Int, block: ClassWriter.() -> Unit): ClassWriter =
-    ClassWriter(flags).apply(block)
+internal inline fun ClassWriter(flags: Int, block: ClassWriter.() -> Unit): ClassWriter {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return ClassWriter(flags).apply(block)
+}
 
 internal inline fun ClassWriter.visitField(
     access: Int,
@@ -74,7 +83,10 @@ internal inline fun ClassWriter.visitField(
     signature: String?,
     value: Any?,
     block: FieldVisitor.() -> Unit
-): FieldVisitor = visitField(access, name, descriptor, signature, value).apply(block)
+): FieldVisitor {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return visitField(access, name, descriptor, signature, value).apply(block)
+}
 
 private fun <T> AsmBuilder<T>.findSpecific(context: Algebra<T>, name: String, parameterTypes: Array<MstType>): Method? =
     context.javaClass.methods.find { method ->
@@ -158,6 +170,7 @@ internal inline fun <T> AsmBuilder<T>.buildAlgebraOperationCall(
     parameterTypes: Array<MstType>,
     parameters: AsmBuilder<T>.() -> Unit
 ) {
+    contract { callsInPlace(parameters, InvocationKind.EXACTLY_ONCE) }
     val arity = parameterTypes.size
     loadAlgebra()
     if (!buildExpectationStack(context, name, parameterTypes)) loadStringConstant(name)

kmath-ast/src/jvmTest/kotlin/scietifik/kmath/ast/ParserPrecedenceTest.kt

@@ -0,0 +1,36 @@
+package scietifik.kmath.ast
+
+import scientifik.kmath.ast.evaluate
+import scientifik.kmath.ast.parseMath
+import scientifik.kmath.operations.Field
+import scientifik.kmath.operations.RealField
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+internal class ParserPrecedenceTest {
+    private val f: Field<Double> = RealField
+
+    @Test
+    fun test1(): Unit = assertEquals(6.0, f.evaluate("2*2+2".parseMath()))
+
+    @Test
+    fun test2(): Unit = assertEquals(6.0, f.evaluate("2+2*2".parseMath()))
+
+    @Test
+    fun test3(): Unit = assertEquals(10.0, f.evaluate("2^3+2".parseMath()))
+
+    @Test
+    fun test4(): Unit = assertEquals(10.0, f.evaluate("2+2^3".parseMath()))
+
+    @Test
+    fun test5(): Unit = assertEquals(16.0, f.evaluate("2^3*2".parseMath()))
+
+    @Test
+    fun test6(): Unit = assertEquals(16.0, f.evaluate("2*2^3".parseMath()))
+
+    @Test
+    fun test7(): Unit = assertEquals(18.0, f.evaluate("2+2^3*2".parseMath()))
+
+    @Test
+    fun test8(): Unit = assertEquals(18.0, f.evaluate("2*2^3+2".parseMath()))
+}

kmath-ast/src/jvmTest/kotlin/scietifik/kmath/ast/ParserTest.kt

@@ -4,8 +4,10 @@ import scientifik.kmath.ast.evaluate
 import scientifik.kmath.ast.mstInField
 import scientifik.kmath.ast.parseMath
 import scientifik.kmath.expressions.invoke
+import scientifik.kmath.operations.Algebra
 import scientifik.kmath.operations.Complex
 import scientifik.kmath.operations.ComplexField
+import scientifik.kmath.operations.RealField
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
@@ -22,4 +24,37 @@ internal class ParserTest {
         val res = ComplexField.mstInField { number(2) + number(2) * (number(2) + number(2)) }()
         assertEquals(Complex(10.0, 0.0), res)
     }
+
+    @Test
+    fun `evaluate MST with singular`() {
+        val mst = "i".parseMath()
+        val res = ComplexField.evaluate(mst)
+        assertEquals(ComplexField.i, res)
+    }
+
+
+    @Test
+    fun `evaluate MST with unary function`() {
+        val mst = "sin(0)".parseMath()
+        val res = RealField.evaluate(mst)
+        assertEquals(0.0, res)
+    }
+
+    @Test
+    fun `evaluate MST with binary function`() {
+        val magicalAlgebra = object : Algebra<String> {
+            override fun symbol(value: String): String = value
+
+            override fun unaryOperation(operation: String, arg: String): String = throw NotImplementedError()
+
+            override fun binaryOperation(operation: String, left: String, right: String): String = when (operation) {
+                "magic" -> "$left ★ $right"
+                else -> throw NotImplementedError()
+            }
+        }
+
+        val mst = "magic(a, b)".parseMath()
+        val res = magicalAlgebra.evaluate(mst)
+        assertEquals("a ★ b", res)
+    }
 }

kmath-commons/build.gradle.kts

@@ -1,7 +1,4 @@
-plugins {
-    id("scientifik.jvm")
-}
-
+plugins { id("scientifik.jvm") }
 description = "Commons math binding for kmath"
 
 dependencies {
@@ -11,3 +8,5 @@ dependencies {
     api(project(":kmath-functions"))
     api("org.apache.commons:commons-math3:3.6.1")
 }
+
+kotlin.sourceSets.all { languageSettings.useExperimentalAnnotation("kotlin.contracts.ExperimentalContracts") }

kmath-commons/src/main/kotlin/scientifik/kmath/commons/expressions/DiffExpression.kt

@@ -5,6 +5,7 @@ import scientifik.kmath.expressions.Expression
 import scientifik.kmath.expressions.ExpressionAlgebra
 import scientifik.kmath.operations.ExtendedField
 import scientifik.kmath.operations.Field
+import scientifik.kmath.operations.invoke
 import kotlin.properties.ReadOnlyProperty
 import kotlin.reflect.KProperty
 
@@ -15,26 +16,22 @@ class DerivativeStructureField(
     val order: Int,
     val parameters: Map<String, Double>
 ) : ExtendedField<DerivativeStructure> {
-
     override val zero: DerivativeStructure by lazy { DerivativeStructure(order, parameters.size) }
-
     override val one: DerivativeStructure by lazy { DerivativeStructure(order, parameters.size, 1.0) }
 
     private val variables: Map<String, DerivativeStructure> = parameters.mapValues { (key, value) ->
         DerivativeStructure(parameters.size, order, parameters.keys.indexOf(key), value)
     }
 
-    val variable = object : ReadOnlyProperty<Any?, DerivativeStructure> {
-        override fun getValue(thisRef: Any?, property: KProperty<*>): DerivativeStructure {
-            return variables[property.name] ?: error("A variable with name ${property.name} does not exist")
-        }
+    val variable: ReadOnlyProperty<Any?, DerivativeStructure> = object : ReadOnlyProperty<Any?, DerivativeStructure> {
+        override fun getValue(thisRef: Any?, property: KProperty<*>): DerivativeStructure =
+            variables[property.name] ?: error("A variable with name ${property.name} does not exist")
     }
 
     fun variable(name: String, default: DerivativeStructure? = null): DerivativeStructure =
         variables[name] ?: default ?: error("A variable with name $name does not exist")
 
-
-    fun Number.const() = DerivativeStructure(order, parameters.size, toDouble())
+    fun Number.const(): DerivativeStructure = DerivativeStructure(order, parameters.size, toDouble())
 
     fun DerivativeStructure.deriv(parName: String, order: Int = 1): Double {
         return deriv(mapOf(parName to order))
@@ -60,10 +57,18 @@ class DerivativeStructureField(
 
     override fun sin(arg: DerivativeStructure): DerivativeStructure = arg.sin()
     override fun cos(arg: DerivativeStructure): DerivativeStructure = arg.cos()
+    override fun tan(arg: DerivativeStructure): DerivativeStructure = arg.tan()
     override fun asin(arg: DerivativeStructure): DerivativeStructure = arg.asin()
     override fun acos(arg: DerivativeStructure): DerivativeStructure = arg.acos()
     override fun atan(arg: DerivativeStructure): DerivativeStructure = arg.atan()
 
+    override fun sinh(arg: DerivativeStructure): DerivativeStructure = arg.sinh()
+    override fun cosh(arg: DerivativeStructure): DerivativeStructure = arg.cosh()
+    override fun tanh(arg: DerivativeStructure): DerivativeStructure = arg.tanh()
+    override fun asinh(arg: DerivativeStructure): DerivativeStructure = arg.asinh()
+    override fun acosh(arg: DerivativeStructure): DerivativeStructure = arg.acosh()
+    override fun atanh(arg: DerivativeStructure): DerivativeStructure = arg.atanh()
+
     override fun power(arg: DerivativeStructure, pow: Number): DerivativeStructure = when (pow) {
         is Double -> arg.pow(pow)
         is Int -> arg.pow(pow)
@@ -71,23 +76,20 @@ class DerivativeStructureField(
     }
 
     fun power(arg: DerivativeStructure, pow: DerivativeStructure): DerivativeStructure = arg.pow(pow)
-
     override fun exp(arg: DerivativeStructure): DerivativeStructure = arg.exp()
-
     override fun ln(arg: DerivativeStructure): DerivativeStructure = arg.log()
 
     override operator fun DerivativeStructure.plus(b: Number): DerivativeStructure = add(b.toDouble())
     override operator fun DerivativeStructure.minus(b: Number): DerivativeStructure = subtract(b.toDouble())
-    override operator fun Number.plus(b: DerivativeStructure) = b + this
-    override operator fun Number.minus(b: DerivativeStructure) = b - this
+    override operator fun Number.plus(b: DerivativeStructure): DerivativeStructure = b + this
+    override operator fun Number.minus(b: DerivativeStructure): DerivativeStructure = b - this
 }
 
 /**
  * A constructs that creates a derivative structure with required order on-demand
  */
 class DiffExpression(val function: DerivativeStructureField.() -> DerivativeStructure) : Expression<Double> {
-
-    override fun invoke(arguments: Map<String, Double>): Double = DerivativeStructureField(
+    override operator fun invoke(arguments: Map<String, Double>): Double = DerivativeStructureField(
         0,
         arguments
     ).run(function).value
@@ -96,45 +98,40 @@ class DiffExpression(val function: DerivativeStructureField.() -> DerivativeStru
      * Get the derivative expression with given orders
      * TODO make result [DiffExpression]
      */
-    fun derivative(orders: Map<String, Int>): Expression<Double> {
-        return object : Expression<Double> {
-            override fun invoke(arguments: Map<String, Double>): Double =
-                DerivativeStructureField(orders.values.max() ?: 0, arguments)
-                    .run {
-                        function().deriv(orders)
-                    }
-        }
+    fun derivative(orders: Map<String, Int>): Expression<Double> = object : Expression<Double> {
+        override operator fun invoke(arguments: Map<String, Double>): Double =
+            (DerivativeStructureField(orders.values.max() ?: 0, arguments)) { function().deriv(orders) }
     }
 
     //TODO add gradient and maybe other vector operators
 }
 
-fun DiffExpression.derivative(vararg orders: Pair<String, Int>) = derivative(mapOf(*orders))
-fun DiffExpression.derivative(name: String) = derivative(name to 1)
+fun DiffExpression.derivative(vararg orders: Pair<String, Int>): Expression<Double> = derivative(mapOf(*orders))
+fun DiffExpression.derivative(name: String): Expression<Double> = derivative(name to 1)
 
 /**
  * A context for [DiffExpression] (not to be confused with [DerivativeStructure])
  */
 object DiffExpressionAlgebra : ExpressionAlgebra<Double, DiffExpression>, Field<DiffExpression> {
-    override fun variable(name: String, default: Double?) =
+    override fun variable(name: String, default: Double?): DiffExpression =
         DiffExpression { variable(name, default?.const()) }
 
     override fun const(value: Double): DiffExpression =
         DiffExpression { value.const() }
 
-    override fun add(a: DiffExpression, b: DiffExpression) =
+    override fun add(a: DiffExpression, b: DiffExpression): DiffExpression =
         DiffExpression { a.function(this) + b.function(this) }
 
-    override val zero = DiffExpression { 0.0.const() }
+    override val zero: DiffExpression = DiffExpression { 0.0.const() }
 
-    override fun multiply(a: DiffExpression, k: Number) =
+    override fun multiply(a: DiffExpression, k: Number): DiffExpression =
         DiffExpression { a.function(this) * k }
 
-    override val one = DiffExpression { 1.0.const() }
+    override val one: DiffExpression = DiffExpression { 1.0.const() }
 
-    override fun multiply(a: DiffExpression, b: DiffExpression) =
+    override fun multiply(a: DiffExpression, b: DiffExpression): DiffExpression =
         DiffExpression { a.function(this) * b.function(this) }
 
-    override fun divide(a: DiffExpression, b: DiffExpression) =
+    override fun divide(a: DiffExpression, b: DiffExpression): DiffExpression =
         DiffExpression { a.function(this) / b.function(this) }
 }

kmath-commons/src/main/kotlin/scientifik/kmath/commons/linear/CMMatrix.kt

@@ -1,8 +1,6 @@
 package scientifik.kmath.commons.linear
 
 import org.apache.commons.math3.linear.*
-import org.apache.commons.math3.linear.RealMatrix
-import org.apache.commons.math3.linear.RealVector
 import scientifik.kmath.linear.*
 import scientifik.kmath.structures.Matrix
 import scientifik.kmath.structures.NDStructure
@@ -14,12 +12,12 @@ class CMMatrix(val origin: RealMatrix, features: Set<MatrixFeature>? = null) :
 
     override val features: Set<MatrixFeature> = features ?: sequence<MatrixFeature> {
         if (origin is DiagonalMatrix) yield(DiagonalFeature)
-    }.toSet()
+    }.toHashSet()
 
-    override fun suggestFeature(vararg features: MatrixFeature) =
+    override fun suggestFeature(vararg features: MatrixFeature): CMMatrix =
         CMMatrix(origin, this.features + features)
 
-    override fun get(i: Int, j: Int): Double = origin.getEntry(i, j)
+    override operator fun get(i: Int, j: Int): Double = origin.getEntry(i, j)
 
     override fun equals(other: Any?): Boolean {
         return NDStructure.equals(this, other as? NDStructure<*> ?: return false)
@@ -40,24 +38,22 @@ fun Matrix<Double>.toCM(): CMMatrix = if (this is CMMatrix) {
     CMMatrix(Array2DRowRealMatrix(array))
 }
 
-fun RealMatrix.asMatrix() = CMMatrix(this)
+fun RealMatrix.asMatrix(): CMMatrix = CMMatrix(this)
 
 class CMVector(val origin: RealVector) : Point<Double> {
     override val size: Int get() = origin.dimension
 
-    override fun get(index: Int): Double = origin.getEntry(index)
+    override operator fun get(index: Int): Double = origin.getEntry(index)
 
-    override fun iterator(): Iterator<Double> = origin.toArray().iterator()
+    override operator fun iterator(): Iterator<Double> = origin.toArray().iterator()
 }
 
-fun Point<Double>.toCM(): CMVector = if (this is CMVector) {
-    this
-} else {
+fun Point<Double>.toCM(): CMVector = if (this is CMVector) this else {
     val array = DoubleArray(size) { this[it] }
     CMVector(ArrayRealVector(array))
 }
 
-fun RealVector.toPoint() = CMVector(this)
+fun RealVector.toPoint(): CMVector = CMVector(this)
 
 object CMMatrixContext : MatrixContext<Double> {
     override fun produce(rows: Int, columns: Int, initializer: (i: Int, j: Int) -> Double): CMMatrix {
@@ -65,30 +61,31 @@ object CMMatrixContext : MatrixContext<Double> {
         return CMMatrix(Array2DRowRealMatrix(array))
     }
 
-    override fun Matrix<Double>.dot(other: Matrix<Double>) =
+    override fun Matrix<Double>.dot(other: Matrix<Double>): CMMatrix =
         CMMatrix(this.toCM().origin.multiply(other.toCM().origin))
 
     override fun Matrix<Double>.dot(vector: Point<Double>): CMVector =
         CMVector(this.toCM().origin.preMultiply(vector.toCM().origin))
 
-    override fun Matrix<Double>.unaryMinus(): CMMatrix =
+    override operator fun Matrix<Double>.unaryMinus(): CMMatrix =
         produce(rowNum, colNum) { i, j -> -get(i, j) }
 
-    override fun add(a: Matrix<Double>, b: Matrix<Double>) =
+    override fun add(a: Matrix<Double>, b: Matrix<Double>): CMMatrix =
         CMMatrix(a.toCM().origin.multiply(b.toCM().origin))
 
-    override fun Matrix<Double>.minus(b: Matrix<Double>) =
+    override operator fun Matrix<Double>.minus(b: Matrix<Double>): CMMatrix =
         CMMatrix(this.toCM().origin.subtract(b.toCM().origin))
 
-    override fun multiply(a: Matrix<Double>, k: Number) =
+    override fun multiply(a: Matrix<Double>, k: Number): CMMatrix =
         CMMatrix(a.toCM().origin.scalarMultiply(k.toDouble()))
 
-    override fun Matrix<Double>.times(value: Double): Matrix<Double>  =
+    override operator fun Matrix<Double>.times(value: Double): Matrix<Double> =
         produce(rowNum, colNum) { i, j -> get(i, j) * value }
 }
 
 operator fun CMMatrix.plus(other: CMMatrix): CMMatrix =
     CMMatrix(this.origin.add(other.origin))
+
 operator fun CMMatrix.minus(other: CMMatrix): CMMatrix =
     CMMatrix(this.origin.subtract(other.origin))
 

kmath-commons/src/main/kotlin/scientifik/kmath/commons/random/CMRandomGeneratorWrapper.kt

@@ -4,10 +4,9 @@ import scientifik.kmath.prob.RandomGenerator
 
 class CMRandomGeneratorWrapper(val factory: (IntArray) -> RandomGenerator) :
     org.apache.commons.math3.random.RandomGenerator {
-    private var generator = factory(intArrayOf())
+    private var generator: RandomGenerator = factory(intArrayOf())
 
     override fun nextBoolean(): Boolean = generator.nextBoolean()
-
     override fun nextFloat(): Float = generator.nextDouble().toFloat()
 
     override fun setSeed(seed: Int) {
@@ -27,12 +26,8 @@ class CMRandomGeneratorWrapper(val factory: (IntArray) -> RandomGenerator) :
     }
 
     override fun nextInt(): Int = generator.nextInt()
-
     override fun nextInt(n: Int): Int = generator.nextInt(n)
-
     override fun nextGaussian(): Double = TODO()
-
     override fun nextDouble(): Double = generator.nextDouble()
-
     override fun nextLong(): Long = generator.nextLong()
 }

kmath-commons/src/test/kotlin/scientifik/kmath/commons/expressions/AutoDiffTest.kt

@@ -1,11 +1,15 @@
 package scientifik.kmath.commons.expressions
 
 import scientifik.kmath.expressions.invoke
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
-inline fun <R> diff(order: Int, vararg parameters: Pair<String, Double>, block: DerivativeStructureField.() -> R) =
-    DerivativeStructureField(order, mapOf(*parameters)).run(block)
+inline fun <R> diff(order: Int, vararg parameters: Pair<String, Double>, block: DerivativeStructureField.() -> R): R {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return DerivativeStructureField(order, mapOf(*parameters)).run(block)
+}
 
 class AutoDiffTest {
     @Test

kmath-core/README.md

@@ -0,0 +1,40 @@
+# The Core Module (`kmath-core`)
+
+The core features of KMath:
+
+- Algebraic structures: contexts and elements.
+- ND structures.
+- Buffers.
+- Functional Expressions.
+- Domains.
+- Automatic differentiation.
+
+> #### Artifact:
+> This module is distributed in the artifact `scientifik:kmath-core:0.1.4-dev-8`.
+> 
+> **Gradle:**
+>
+> ```gradle
+> repositories {
+>     maven { url 'https://dl.bintray.com/mipt-npm/scientifik' }
+>     maven { url 'https://dl.bintray.com/mipt-npm/dev' }
+>     maven { url https://dl.bintray.com/hotkeytlt/maven' }
+> }
+> 
+> dependencies {
+>     implementation 'scientifik:kmath-core:0.1.4-dev-8'
+> }
+> ```
+> **Gradle Kotlin DSL:**
+>
+> ```kotlin
+> repositories {
+>     maven("https://dl.bintray.com/mipt-npm/scientifik")
+>     maven("https://dl.bintray.com/mipt-npm/dev")
+>     maven("https://dl.bintray.com/hotkeytlt/maven")
+> }
+> 
+> dependencies {``
+>     implementation("scientifik:kmath-core:0.1.4-dev-8")
+> }
+> ```

kmath-core/build.gradle.kts

@@ -1,11 +1,6 @@
-plugins {
-    id("scientifik.mpp")
-}
+plugins { id("scientifik.mpp") }
 
 kotlin.sourceSets {
-    commonMain {
-        dependencies {
-            api(project(":kmath-memory"))
-        }
-    }
+    all { languageSettings.useExperimentalAnnotation("kotlin.contracts.ExperimentalContracts") }
+    commonMain { dependencies { api(project(":kmath-memory")) } }
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/domains/Domain.kt

@@ -3,13 +3,18 @@ package scientifik.kmath.domains
 import scientifik.kmath.linear.Point
 
 /**
- * A simple geometric domain
+ * A simple geometric domain.
+ *
+ * @param T the type of element of this domain.
  */
 interface Domain<T : Any> {
+    /**
+     * Checks if the specified point is contained in this domain.
+     */
     operator fun contains(point: Point<T>): Boolean
 
     /**
-     * Number of hyperspace dimensions
+     * Number of hyperspace dimensions.
      */
     val dimension: Int
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/domains/HyperSquareDomain.kt

@@ -42,13 +42,14 @@ class HyperSquareDomain(private val lower: RealBuffer, private val upper: RealBu
     override fun getUpperBound(num: Int): Double? = upper[num]
 
     override fun nearestInDomain(point: Point<Double>): Point<Double> {
-        val res: DoubleArray = DoubleArray(point.size) { i ->
+        val res = DoubleArray(point.size) { i ->
             when {
                 point[i] < lower[i] -> lower[i]
                 point[i] > upper[i] -> upper[i]
                 else -> point[i]
             }
         }
+
         return RealBuffer(*res)
     }
 

kmath-core/src/commonMain/kotlin/scientifik/kmath/domains/RealDomain.kt

@@ -22,8 +22,7 @@ import scientifik.kmath.linear.Point
  *
  * @author Alexander Nozik
  */
-interface RealDomain: Domain<Double> {
-
+interface RealDomain : Domain<Double> {
     fun nearestInDomain(point: Point<Double>): Point<Double>
 
     /**
@@ -61,5 +60,4 @@ interface RealDomain: Domain<Double> {
      * @return
      */
     fun volume(): Double
-
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/domains/UnconstrainedDomain.kt

@@ -18,7 +18,6 @@ package scientifik.kmath.domains
 import scientifik.kmath.linear.Point
 
 class UnconstrainedDomain(override val dimension: Int) : RealDomain {
-
     override operator fun contains(point: Point<Double>): Boolean = true
 
     override fun getLowerBound(num: Int, point: Point<Double>): Double? = Double.NEGATIVE_INFINITY
@@ -32,5 +31,4 @@ class UnconstrainedDomain(override val dimension: Int) : RealDomain {
     override fun nearestInDomain(point: Point<Double>): Point<Double> = point
 
     override fun volume(): Double = Double.POSITIVE_INFINITY
-
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/domains/UnivariateDomain.kt

@@ -4,7 +4,6 @@ import scientifik.kmath.linear.Point
 import scientifik.kmath.structures.asBuffer
 
 inline class UnivariateDomain(val range: ClosedFloatingPointRange<Double>) : RealDomain {
-
     operator fun contains(d: Double): Boolean = range.contains(d)
 
     override operator fun contains(point: Point<Double>): Boolean {
@@ -15,7 +14,7 @@ inline class UnivariateDomain(val range: ClosedFloatingPointRange<Double>) : Rea
     override fun nearestInDomain(point: Point<Double>): Point<Double> {
         require(point.size == 1)
         val value = point[0]
-        return when{
+        return when {
             value in range -> point
             value >= range.endInclusive -> doubleArrayOf(range.endInclusive).asBuffer()
             else -> doubleArrayOf(range.start).asBuffer()

kmath-core/src/commonMain/kotlin/scientifik/kmath/expressions/Builders.kt

@@ -1,23 +1,41 @@
 package scientifik.kmath.expressions
 
+import scientifik.kmath.operations.ExtendedField
 import scientifik.kmath.operations.Field
 import scientifik.kmath.operations.Ring
 import scientifik.kmath.operations.Space
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 
 /**
- * Create a functional expression on this [Space]
+ * Creates a functional expression with this [Space].
  */
-fun <T> Space<T>.spaceExpression(block: FunctionalExpressionSpace<T, Space<T>>.() -> Expression<T>): Expression<T> =
-    FunctionalExpressionSpace(this).run(block)
+inline fun <T> Space<T>.spaceExpression(block: FunctionalExpressionSpace<T, Space<T>>.() -> Expression<T>): Expression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return FunctionalExpressionSpace(this).block()
+}
 
 /**
- * Create a functional expression on this [Ring]
+ * Creates a functional expression with this [Ring].
  */
-fun <T> Ring<T>.ringExpression(block: FunctionalExpressionRing<T, Ring<T>>.() -> Expression<T>): Expression<T> =
-    FunctionalExpressionRing(this).run(block)
+inline fun <T> Ring<T>.ringExpression(block: FunctionalExpressionRing<T, Ring<T>>.() -> Expression<T>): Expression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return FunctionalExpressionRing(this).block()
+}
 
 /**
- * Create a functional expression on this [Field]
+ * Creates a functional expression with this [Field].
  */
-fun <T> Field<T>.fieldExpression(block: FunctionalExpressionField<T, Field<T>>.() -> Expression<T>): Expression<T> =
-    FunctionalExpressionField(this).run(block)
+inline fun <T> Field<T>.fieldExpression(block: FunctionalExpressionField<T, Field<T>>.() -> Expression<T>): Expression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return FunctionalExpressionField(this).block()
+}
+
+/**
+ * Creates a functional expression with this [ExtendedField].
+ */
+inline fun <T> ExtendedField<T>.extendedFieldExpression(block: FunctionalExpressionExtendedField<T, ExtendedField<T>>.() -> Expression<T>): Expression<T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return FunctionalExpressionExtendedField(this).block()
+}

kmath-core/src/commonMain/kotlin/scientifik/kmath/expressions/Expression.kt

@@ -6,6 +6,12 @@ import scientifik.kmath.operations.Algebra
  * An elementary function that could be invoked on a map of arguments
  */
 interface Expression<T> {
+    /**
+     * Calls this expression from arguments.
+     *
+     * @param arguments the map of arguments.
+     * @return the value.
+     */
     operator fun invoke(arguments: Map<String, T>): T
 
     companion object
@@ -14,10 +20,17 @@ interface Expression<T> {
 /**
  * Create simple lazily evaluated expression inside given algebra
  */
-fun <T> Algebra<T>.expression(block:  Algebra<T>.(arguments: Map<String, T>) -> T): Expression<T> = object: Expression<T> {
-    override fun invoke(arguments: Map<String, T>): T = block(arguments)
-}
+fun <T> Algebra<T>.expression(block: Algebra<T>.(arguments: Map<String, T>) -> T): Expression<T> =
+    object : Expression<T> {
+        override operator fun invoke(arguments: Map<String, T>): T = block(arguments)
+    }
 
+/**
+ * Calls this expression from arguments.
+ *
+ * @param pairs the pair of arguments' names to values.
+ * @return the value.
+ */
 operator fun <T> Expression<T>.invoke(vararg pairs: Pair<String, T>): T = invoke(mapOf(*pairs))
 
 /**

kmath-core/src/commonMain/kotlin/scientifik/kmath/expressions/FunctionalExpressionAlgebra.kt

@@ -4,7 +4,7 @@ import scientifik.kmath.operations.*
 
 internal class FunctionalUnaryOperation<T>(val context: Algebra<T>, val name: String, private val expr: Expression<T>) :
     Expression<T> {
-    override fun invoke(arguments: Map<String, T>): T = context.unaryOperation(name, expr.invoke(arguments))
+    override operator fun invoke(arguments: Map<String, T>): T = context.unaryOperation(name, expr.invoke(arguments))
 }
 
 internal class FunctionalBinaryOperation<T>(
@@ -13,17 +13,17 @@ internal class FunctionalBinaryOperation<T>(
     val first: Expression<T>,
     val second: Expression<T>
 ) : Expression<T> {
-    override fun invoke(arguments: Map<String, T>): T =
+    override operator fun invoke(arguments: Map<String, T>): T =
         context.binaryOperation(name, first.invoke(arguments), second.invoke(arguments))
 }
 
 internal class FunctionalVariableExpression<T>(val name: String, val default: T? = null) : Expression<T> {
-    override fun invoke(arguments: Map<String, T>): T =
+    override operator fun invoke(arguments: Map<String, T>): T =
         arguments[name] ?: default ?: error("Parameter not found: $name")
 }
 
 internal class FunctionalConstantExpression<T>(val value: T) : Expression<T> {
-    override fun invoke(arguments: Map<String, T>): T = value
+    override operator fun invoke(arguments: Map<String, T>): T = value
 }
 
 internal class FunctionalConstProductExpression<T>(
@@ -31,7 +31,7 @@ internal class FunctionalConstProductExpression<T>(
     private val expr: Expression<T>,
     val const: Number
 ) : Expression<T> {
-    override fun invoke(arguments: Map<String, T>): T = context.multiply(expr.invoke(arguments), const)
+    override operator fun invoke(arguments: Map<String, T>): T = context.multiply(expr.invoke(arguments), const)
 }
 
 /**
@@ -40,7 +40,6 @@ internal class FunctionalConstProductExpression<T>(
  * @param algebra The algebra to provide for Expressions built.
  */
 abstract class FunctionalExpressionAlgebra<T, A : Algebra<T>>(val algebra: A) : ExpressionAlgebra<T, Expression<T>> {
-
     /**
      * Builds an Expression of constant expression which does not depend on arguments.
      */
@@ -69,14 +68,13 @@ abstract class FunctionalExpressionAlgebra<T, A : Algebra<T>>(val algebra: A) :
  */
 open class FunctionalExpressionSpace<T, A : Space<T>>(algebra: A) :
     FunctionalExpressionAlgebra<T, A>(algebra), Space<Expression<T>> {
-
     override val zero: Expression<T> get() = const(algebra.zero)
 
     /**
      * Builds an Expression of addition of two another expressions.
      */
     override fun add(a: Expression<T>, b: Expression<T>): Expression<T> =
-        FunctionalBinaryOperation(algebra, SpaceOperations.PLUS_OPERATION, a, b)
+        binaryOperation(SpaceOperations.PLUS_OPERATION, a, b)
 
     /**
      * Builds an Expression of multiplication of expression by number.
@@ -105,7 +103,7 @@ open class FunctionalExpressionRing<T, A>(algebra: A) : FunctionalExpressionSpac
      * Builds an Expression of multiplication of two expressions.
      */
     override fun multiply(a: Expression<T>, b: Expression<T>): Expression<T> =
-        FunctionalBinaryOperation(algebra, RingOperations.TIMES_OPERATION, a, b)
+        binaryOperation(RingOperations.TIMES_OPERATION, a, b)
 
     operator fun Expression<T>.times(arg: T): Expression<T> = this * const(arg)
     operator fun T.times(arg: Expression<T>): Expression<T> = arg * this
@@ -124,7 +122,7 @@ open class FunctionalExpressionField<T, A>(algebra: A) :
      * Builds an Expression of division an expression by another one.
      */
     override fun divide(a: Expression<T>, b: Expression<T>): Expression<T> =
-        FunctionalBinaryOperation(algebra, FieldOperations.DIV_OPERATION, a, b)
+        binaryOperation(FieldOperations.DIV_OPERATION, a, b)
 
     operator fun Expression<T>.div(arg: T): Expression<T> = this / const(arg)
     operator fun T.div(arg: Expression<T>): Expression<T> = arg / this
@@ -136,6 +134,28 @@ open class FunctionalExpressionField<T, A>(algebra: A) :
         super<FunctionalExpressionRing>.binaryOperation(operation, left, right)
 }
 
+open class FunctionalExpressionExtendedField<T, A>(algebra: A) :
+    FunctionalExpressionField<T, A>(algebra),
+    ExtendedField<Expression<T>> where A : ExtendedField<T>, A : NumericAlgebra<T> {
+    override fun sin(arg: Expression<T>): Expression<T> = unaryOperation(TrigonometricOperations.SIN_OPERATION, arg)
+    override fun cos(arg: Expression<T>): Expression<T> = unaryOperation(TrigonometricOperations.COS_OPERATION, arg)
+    override fun asin(arg: Expression<T>): Expression<T> = unaryOperation(TrigonometricOperations.ASIN_OPERATION, arg)
+    override fun acos(arg: Expression<T>): Expression<T> = unaryOperation(TrigonometricOperations.ACOS_OPERATION, arg)
+    override fun atan(arg: Expression<T>): Expression<T> = unaryOperation(TrigonometricOperations.ATAN_OPERATION, arg)
+
+    override fun power(arg: Expression<T>, pow: Number): Expression<T> =
+        binaryOperation(PowerOperations.POW_OPERATION, arg, number(pow))
+
+    override fun exp(arg: Expression<T>): Expression<T> = unaryOperation(ExponentialOperations.EXP_OPERATION, arg)
+    override fun ln(arg: Expression<T>): Expression<T> = unaryOperation(ExponentialOperations.LN_OPERATION, arg)
+
+    override fun unaryOperation(operation: String, arg: Expression<T>): Expression<T> =
+        super<FunctionalExpressionField>.unaryOperation(operation, arg)
+
+    override fun binaryOperation(operation: String, left: Expression<T>, right: Expression<T>): Expression<T> =
+        super<FunctionalExpressionField>.binaryOperation(operation, left, right)
+}
+
 inline fun <T, A : Space<T>> A.expressionInSpace(block: FunctionalExpressionSpace<T, A>.() -> Expression<T>): Expression<T> =
     FunctionalExpressionSpace(this).block()
 
@@ -144,3 +164,6 @@ inline fun <T, A : Ring<T>> A.expressionInRing(block: FunctionalExpressionRing<T
 
 inline fun <T, A : Field<T>> A.expressionInField(block: FunctionalExpressionField<T, A>.() -> Expression<T>): Expression<T> =
     FunctionalExpressionField(this).block()
+
+inline fun <T, A : ExtendedField<T>> A.expressionInExtendedField(block: FunctionalExpressionExtendedField<T, A>.() -> Expression<T>): Expression<T> =
+    FunctionalExpressionExtendedField(this).block()

kmath-core/src/commonMain/kotlin/scientifik/kmath/linear/BufferMatrix.kt

@@ -19,22 +19,20 @@ class BufferMatrixContext<T : Any, R : Ring<T>>(
 
     override fun point(size: Int, initializer: (Int) -> T): Point<T> = bufferFactory(size, initializer)
 
-    companion object {
-
-    }
+    companion object
 }
 
 @Suppress("OVERRIDE_BY_INLINE")
 object RealMatrixContext : GenericMatrixContext<Double, RealField> {
 
-    override val elementContext get() = RealField
+    override val elementContext: RealField get() = RealField
 
     override inline fun produce(rows: Int, columns: Int, initializer: (i: Int, j: Int) -> Double): Matrix<Double> {
         val buffer = RealBuffer(rows * columns) { offset -> initializer(offset / columns, offset % columns) }
         return BufferMatrix(rows, columns, buffer)
     }
 
-    override inline fun point(size: Int, initializer: (Int) -> Double): Point<Double> = RealBuffer(size,initializer)
+    override inline fun point(size: Int, initializer: (Int) -> Double): Point<Double> = RealBuffer(size, initializer)
 }
 
 class BufferMatrix<T : Any>(
@@ -52,19 +50,15 @@ class BufferMatrix<T : Any>(
 
     override val shape: IntArray get() = intArrayOf(rowNum, colNum)
 
-    override fun suggestFeature(vararg features: MatrixFeature) =
+    override fun suggestFeature(vararg features: MatrixFeature): BufferMatrix<T> =
         BufferMatrix(rowNum, colNum, buffer, this.features + features)
 
-    override fun get(index: IntArray): T = get(index[0], index[1])
+    override operator fun get(index: IntArray): T = get(index[0], index[1])
 
-    override fun get(i: Int, j: Int): T = buffer[i * colNum + j]
+    override operator fun get(i: Int, j: Int): T = buffer[i * colNum + j]
 
     override fun elements(): Sequence<Pair<IntArray, T>> = sequence {
-        for (i in 0 until rowNum) {
-            for (j in 0 until colNum) {
-                yield(intArrayOf(i, j) to get(i, j))
-            }
-        }
+        for (i in 0 until rowNum) for (j in 0 until colNum) yield(intArrayOf(i, j) to get(i, j))
     }
 
     override fun equals(other: Any?): Boolean {
@@ -84,8 +78,8 @@ class BufferMatrix<T : Any>(
     override fun toString(): String {
         return if (rowNum <= 5 && colNum <= 5) {
             "Matrix(rowsNum = $rowNum, colNum = $colNum, features=$features)\n" +
-                    rows.asSequence().joinToString(prefix = "(", postfix = ")", separator = "\n ") {
-                        it.asSequence().joinToString(separator = "\t") { it.toString() }
+                    rows.asSequence().joinToString(prefix = "(", postfix = ")", separator = "\n ") { buffer ->
+                        buffer.asSequence().joinToString(separator = "\t") { it.toString() }
                     }
         } else {
             "Matrix(rowsNum = $rowNum, colNum = $colNum, features=$features)"
@@ -97,7 +91,7 @@ class BufferMatrix<T : Any>(
  * Optimized dot product for real matrices
  */
 infix fun BufferMatrix<Double>.dot(other: BufferMatrix<Double>): BufferMatrix<Double> {
-    if (this.colNum != other.rowNum) error("Matrix dot operation dimension mismatch: ($rowNum, $colNum) x (${other.rowNum}, ${other.colNum})")
+    require(colNum == other.rowNum) { "Matrix dot operation dimension mismatch: ($rowNum, $colNum) x (${other.rowNum}, ${other.colNum})" }
 
     val array = DoubleArray(this.rowNum * other.colNum)
 

kmath-core/src/commonMain/kotlin/scientifik/kmath/linear/FeaturedMatrix.kt

@@ -4,6 +4,8 @@ import scientifik.kmath.operations.Ring
 import scientifik.kmath.structures.Matrix
 import scientifik.kmath.structures.Structure2D
 import scientifik.kmath.structures.asBuffer
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 import kotlin.math.sqrt
 
 /**
@@ -23,25 +25,25 @@ interface FeaturedMatrix<T : Any> : Matrix<T> {
      */
     fun suggestFeature(vararg features: MatrixFeature): FeaturedMatrix<T>
 
-    companion object {
-
-    }
+    companion object
 }
 
-fun Structure2D.Companion.real(rows: Int, columns: Int, initializer: (Int, Int) -> Double) =
-    MatrixContext.real.produce(rows, columns, initializer)
+inline fun Structure2D.Companion.real(rows: Int, columns: Int, initializer: (Int, Int) -> Double): Matrix<Double> {
+    contract { callsInPlace(initializer) }
+    return MatrixContext.real.produce(rows, columns, initializer)
+}
 
 /**
  * Build a square matrix from given elements.
  */
 fun <T : Any> Structure2D.Companion.square(vararg elements: T): FeaturedMatrix<T> {
     val size: Int = sqrt(elements.size.toDouble()).toInt()
-    if (size * size != elements.size) error("The number of elements ${elements.size} is not a full square")
+    require(size * size == elements.size) { "The number of elements ${elements.size} is not a full square" }
     val buffer = elements.asBuffer()
     return BufferMatrix(size, size, buffer)
 }
 
-val Matrix<*>.features get() = (this as? FeaturedMatrix)?.features?: emptySet()
+val Matrix<*>.features: Set<MatrixFeature> get() = (this as? FeaturedMatrix)?.features ?: emptySet()
 
 /**
  * Check if matrix has the given feature class
@@ -68,7 +70,7 @@ fun <T : Any, R : Ring<T>> GenericMatrixContext<T, R>.one(rows: Int, columns: In
  * A virtual matrix of zeroes
  */
 fun <T : Any, R : Ring<T>> GenericMatrixContext<T, R>.zero(rows: Int, columns: Int): FeaturedMatrix<T> =
-    VirtualMatrix<T>(rows, columns) { _, _ -> elementContext.zero }
+    VirtualMatrix(rows, columns) { _, _ -> elementContext.zero }
 
 class TransposedFeature<T : Any>(val original: Matrix<T>) : MatrixFeature
 

kmath-core/src/commonMain/kotlin/scientifik/kmath/linear/LUPDecomposition.kt

@@ -3,6 +3,7 @@ package scientifik.kmath.linear
 import scientifik.kmath.operations.Field
 import scientifik.kmath.operations.RealField
 import scientifik.kmath.operations.Ring
+import scientifik.kmath.operations.invoke
 import scientifik.kmath.structures.BufferAccessor2D
 import scientifik.kmath.structures.Matrix
 import scientifik.kmath.structures.Structure2D
@@ -18,7 +19,7 @@ class LUPDecomposition<T : Any>(
     private val even: Boolean
 ) : LUPDecompositionFeature<T>, DeterminantFeature<T> {
 
-    val elementContext get() = context.elementContext
+    val elementContext: Field<T> get() = context.elementContext
 
     /**
      * Returns the matrix L of the decomposition.
@@ -60,15 +61,13 @@ class LUPDecomposition<T : Any>(
      * @return determinant of the matrix
      */
     override val determinant: T by lazy {
-        with(elementContext) {
-            (0 until lu.shape[0]).fold(if (even) one else -one) { value, i -> value * lu[i, i] }
-        }
+        elementContext { (0 until lu.shape[0]).fold(if (even) one else -one) { value, i -> value * lu[i, i] } }
     }
 
 }
 
-fun <T : Comparable<T>, F : Field<T>> GenericMatrixContext<T, F>.abs(value: T) =
-    if (value > elementContext.zero) value else with(elementContext) { -value }
+fun <T : Comparable<T>, F : Field<T>> GenericMatrixContext<T, F>.abs(value: T): T =
+    if (value > elementContext.zero) value else elementContext { -value }
 
 
 /**
@@ -88,43 +87,34 @@ fun <T : Comparable<T>, F : Field<T>> GenericMatrixContext<T, F>.lup(
 
     //TODO just waits for KEEP-176
     BufferAccessor2D(type, matrix.rowNum, matrix.colNum).run {
-        elementContext.run {
-
+        elementContext {
             val lu = create(matrix)
 
             // Initialize permutation array and parity
-            for (row in 0 until m) {
-                pivot[row] = row
-            }
+            for (row in 0 until m) pivot[row] = row
             var even = true
 
             // Initialize permutation array and parity
-            for (row in 0 until m) {
-                pivot[row] = row
-            }
+            for (row in 0 until m) pivot[row] = row
 
             // Loop over columns
             for (col in 0 until m) {
-
                 // upper
                 for (row in 0 until col) {
                     val luRow = lu.row(row)
                     var sum = luRow[col]
-                    for (i in 0 until row) {
-                        sum -= luRow[i] * lu[i, col]
-                    }
+                    for (i in 0 until row) sum -= luRow[i] * lu[i, col]
                     luRow[col] = sum
                 }
 
                 // lower
                 var max = col // permutation row
                 var largest = -one
+
                 for (row in col until m) {
                     val luRow = lu.row(row)
                     var sum = luRow[col]
-                    for (i in 0 until col) {
-                        sum -= luRow[i] * lu[i, col]
-                    }
+                    for (i in 0 until col) sum -= luRow[i] * lu[i, col]
                     luRow[col] = sum
 
                     // maintain best permutation choice
@@ -135,19 +125,19 @@ fun <T : Comparable<T>, F : Field<T>> GenericMatrixContext<T, F>.lup(
                 }
 
                 // Singularity check
-                if (checkSingular(this@lup.abs(lu[max, col]))) {
-                    error("The matrix is singular")
-                }
+                check(!checkSingular(this@lup.abs(lu[max, col]))) { "The matrix is singular" }
 
                 // Pivot if necessary
                 if (max != col) {
                     val luMax = lu.row(max)
                     val luCol = lu.row(col)
+
                     for (i in 0 until m) {
                         val tmp = luMax[i]
                         luMax[i] = luCol[i]
                         luCol[i] = tmp
                     }
+
                     val temp = pivot[max]
                     pivot[max] = pivot[col]
                     pivot[col] = temp
@@ -156,9 +146,7 @@ fun <T : Comparable<T>, F : Field<T>> GenericMatrixContext<T, F>.lup(
 
                 // Divide the lower elements by the "winning" diagonal elt.
                 val luDiag = lu[col, col]
-                for (row in col + 1 until m) {
-                    lu[row, col] /= luDiag
-                }
+                for (row in col + 1 until m) lu[row, col] /= luDiag
             }
 
             return LUPDecomposition(this@lup, lu.collect(), pivot, even)
@@ -169,33 +157,29 @@ fun <T : Comparable<T>, F : Field<T>> GenericMatrixContext<T, F>.lup(
 inline fun <reified T : Comparable<T>, F : Field<T>> GenericMatrixContext<T, F>.lup(
     matrix: Matrix<T>,
     noinline checkSingular: (T) -> Boolean
-) = lup(T::class, matrix, checkSingular)
+): LUPDecomposition<T> = lup(T::class, matrix, checkSingular)
 
-fun GenericMatrixContext<Double, RealField>.lup(matrix: Matrix<Double>) = lup(Double::class, matrix) { it < 1e-11 }
+fun GenericMatrixContext<Double, RealField>.lup(matrix: Matrix<Double>): LUPDecomposition<Double> =
+    lup(Double::class, matrix) { it < 1e-11 }
 
 fun <T : Any> LUPDecomposition<T>.solve(type: KClass<T>, matrix: Matrix<T>): Matrix<T> {
-
-    if (matrix.rowNum != pivot.size) {
-        error("Matrix dimension mismatch. Expected ${pivot.size}, but got ${matrix.colNum}")
-    }
+    require(matrix.rowNum == pivot.size) { "Matrix dimension mismatch. Expected ${pivot.size}, but got ${matrix.colNum}" }
 
     BufferAccessor2D(type, matrix.rowNum, matrix.colNum).run {
-        elementContext.run {
-
+        elementContext {
             // Apply permutations to b
             val bp = create { _, _ -> zero }
 
-            for (row in 0 until pivot.size) {
+            for (row in pivot.indices) {
                 val bpRow = bp.row(row)
                 val pRow = pivot[row]
-                for (col in 0 until matrix.colNum) {
-                    bpRow[col] = matrix[pRow, col]
-                }
+                for (col in 0 until matrix.colNum) bpRow[col] = matrix[pRow, col]
             }
 
             // Solve LY = b
-            for (col in 0 until pivot.size) {
+            for (col in pivot.indices) {
                 val bpCol = bp.row(col)
+
                 for (i in col + 1 until pivot.size) {
                     val bpI = bp.row(i)
                     val luICol = lu[i, col]
@@ -209,23 +193,21 @@ fun <T : Any> LUPDecomposition<T>.solve(type: KClass<T>, matrix: Matrix<T>): Mat
             for (col in pivot.size - 1 downTo 0) {
                 val bpCol = bp.row(col)
                 val luDiag = lu[col, col]
-                for (j in 0 until matrix.colNum) {
-                    bpCol[j] /= luDiag
-                }
+                for (j in 0 until matrix.colNum) bpCol[j] /= luDiag
+
                 for (i in 0 until col) {
                     val bpI = bp.row(i)
                     val luICol = lu[i, col]
-                    for (j in 0 until matrix.colNum) {
-                        bpI[j] -= bpCol[j] * luICol
-                    }
+                    for (j in 0 until matrix.colNum) bpI[j] -= bpCol[j] * luICol
                 }
             }
+
             return context.produce(pivot.size, matrix.colNum) { i, j -> bp[i, j] }
         }
     }
 }
 
-inline fun <reified T : Any> LUPDecomposition<T>.solve(matrix: Matrix<T>) = solve(T::class, matrix)
+inline fun <reified T : Any> LUPDecomposition<T>.solve(matrix: Matrix<T>): Matrix<T> = solve(T::class, matrix)
 
 /**
  * Solve a linear equation **a*x = b**
@@ -240,13 +222,12 @@ inline fun <reified T : Comparable<T>, F : Field<T>> GenericMatrixContext<T, F>.
     return decomposition.solve(T::class, b)
 }
 
-fun RealMatrixContext.solve(a: Matrix<Double>, b: Matrix<Double>) =
-    solve(a, b) { it < 1e-11 }
+fun RealMatrixContext.solve(a: Matrix<Double>, b: Matrix<Double>): Matrix<Double> = solve(a, b) { it < 1e-11 }
 
 inline fun <reified T : Comparable<T>, F : Field<T>> GenericMatrixContext<T, F>.inverse(
     matrix: Matrix<T>,
     noinline checkSingular: (T) -> Boolean
-) = solve(matrix, one(matrix.rowNum, matrix.colNum), checkSingular)
+): Matrix<T> = solve(matrix, one(matrix.rowNum, matrix.colNum), checkSingular)
 
-fun RealMatrixContext.inverse(matrix: Matrix<Double>) =
+fun RealMatrixContext.inverse(matrix: Matrix<Double>): Matrix<Double> =
     solve(matrix, one(matrix.rowNum, matrix.colNum)) { it < 1e-11 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/linear/LinearAlgebra.kt

@@ -25,4 +25,4 @@ fun <T : Any> Matrix<T>.asPoint(): Point<T> =
         error("Can't convert matrix with more than one column to vector")
     }
 
-fun <T : Any> Point<T>.asMatrix() = VirtualMatrix(size, 1) { i, _ -> get(i) }
+fun <T : Any> Point<T>.asMatrix(): VirtualMatrix<T> = VirtualMatrix(size, 1) { i, _ -> get(i) }

kmath-core/src/commonMain/kotlin/scientifik/kmath/linear/MatrixBuilder.kt

@@ -7,7 +7,7 @@ import scientifik.kmath.structures.asBuffer
 
 class MatrixBuilder(val rows: Int, val columns: Int) {
     operator fun <T : Any> invoke(vararg elements: T): FeaturedMatrix<T> {
-        if (rows * columns != elements.size) error("The number of elements ${elements.size} is not equal $rows * $columns")
+        require(rows * columns == elements.size) { "The number of elements ${elements.size} is not equal $rows * $columns" }
         val buffer = elements.asBuffer()
         return BufferMatrix(rows, columns, buffer)
     }

kmath-core/src/commonMain/kotlin/scientifik/kmath/linear/MatrixContext.kt

@@ -2,6 +2,7 @@ package scientifik.kmath.linear
 
 import scientifik.kmath.operations.Ring
 import scientifik.kmath.operations.SpaceOperations
+import scientifik.kmath.operations.invoke
 import scientifik.kmath.operations.sum
 import scientifik.kmath.structures.Buffer
 import scientifik.kmath.structures.BufferFactory
@@ -29,7 +30,7 @@ interface MatrixContext<T : Any> : SpaceOperations<Matrix<T>> {
         /**
          * Non-boxing double matrix
          */
-        val real = RealMatrixContext
+        val real: RealMatrixContext = RealMatrixContext
 
         /**
          * A structured matrix with custom buffer
@@ -37,8 +38,7 @@ interface MatrixContext<T : Any> : SpaceOperations<Matrix<T>> {
         fun <T : Any, R : Ring<T>> buffered(
             ring: R,
             bufferFactory: BufferFactory<T> = Buffer.Companion::boxing
-        ): GenericMatrixContext<T, R> =
-            BufferMatrixContext(ring, bufferFactory)
+        ): GenericMatrixContext<T, R> = BufferMatrixContext(ring, bufferFactory)
 
         /**
          * Automatic buffered matrix, unboxed if it is possible
@@ -61,45 +61,49 @@ interface GenericMatrixContext<T : Any, R : Ring<T>> : MatrixContext<T> {
 
     override infix fun Matrix<T>.dot(other: Matrix<T>): Matrix<T> {
         //TODO add typed error
-        if (this.colNum != other.rowNum) error("Matrix dot operation dimension mismatch: ($rowNum, $colNum) x (${other.rowNum}, ${other.colNum})")
+        require(colNum == other.rowNum) { "Matrix dot operation dimension mismatch: ($rowNum, $colNum) x (${other.rowNum}, ${other.colNum})" }
+
         return produce(rowNum, other.colNum) { i, j ->
             val row = rows[i]
             val column = other.columns[j]
-            with(elementContext) {
-                sum(row.asSequence().zip(column.asSequence(), ::multiply))
-            }
+            elementContext { sum(row.asSequence().zip(column.asSequence(), ::multiply)) }
         }
     }
 
     override infix fun Matrix<T>.dot(vector: Point<T>): Point<T> {
         //TODO add typed error
-        if (this.colNum != vector.size) error("Matrix dot vector operation dimension mismatch: ($rowNum, $colNum) x (${vector.size})")
+        require(colNum == vector.size) { "Matrix dot vector operation dimension mismatch: ($rowNum, $colNum) x (${vector.size})" }
+
         return point(rowNum) { i ->
             val row = rows[i]
-            with(elementContext) {
-                sum(row.asSequence().zip(vector.asSequence(), ::multiply))
-            }
+            elementContext { sum(row.asSequence().zip(vector.asSequence(), ::multiply)) }
         }
     }
 
-    override operator fun Matrix<T>.unaryMinus() =
-        produce(rowNum, colNum) { i, j -> elementContext.run { -get(i, j) } }
+    override operator fun Matrix<T>.unaryMinus(): Matrix<T> =
+        produce(rowNum, colNum) { i, j -> elementContext { -get(i, j) } }
 
     override fun add(a: Matrix<T>, b: Matrix<T>): Matrix<T> {
-        if (a.rowNum != b.rowNum || a.colNum != b.colNum) error("Matrix operation dimension mismatch. [${a.rowNum},${a.colNum}] + [${b.rowNum},${b.colNum}]")
-        return produce(a.rowNum, a.colNum) { i, j -> elementContext.run { a.get(i, j) + b[i, j] } }
+        require(a.rowNum == b.rowNum && a.colNum == b.colNum) {
+            "Matrix operation dimension mismatch. [${a.rowNum},${a.colNum}] + [${b.rowNum},${b.colNum}]"
+        }
+
+        return produce(a.rowNum, a.colNum) { i, j -> elementContext { a[i, j] + b[i, j] } }
     }
 
     override operator fun Matrix<T>.minus(b: Matrix<T>): Matrix<T> {
-        if (rowNum != b.rowNum || colNum != b.colNum) error("Matrix operation dimension mismatch. [$rowNum,$colNum] - [${b.rowNum},${b.colNum}]")
-        return produce(rowNum, colNum) { i, j -> elementContext.run { get(i, j) + b[i, j] } }
+        require(rowNum == b.rowNum && colNum == b.colNum) {
+            "Matrix operation dimension mismatch. [$rowNum,$colNum] - [${b.rowNum},${b.colNum}]"
+        }
+
+        return produce(rowNum, colNum) { i, j -> elementContext { get(i, j) + b[i, j] } }
     }
 
     override fun multiply(a: Matrix<T>, k: Number): Matrix<T> =
-        produce(a.rowNum, a.colNum) { i, j -> elementContext.run { a.get(i, j) * k } }
+        produce(a.rowNum, a.colNum) { i, j -> elementContext { a[i, j] * k } }
 
     operator fun Number.times(matrix: FeaturedMatrix<T>): Matrix<T> = matrix * this
 
-    override fun Matrix<T>.times(value: T): Matrix<T> =
-        produce(rowNum, colNum) { i, j -> elementContext.run { get(i, j) * value } }
+    override operator fun Matrix<T>.times(value: T): Matrix<T> =
+        produce(rowNum, colNum) { i, j -> elementContext { get(i, j) * value } }
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/linear/MatrixFeatures.kt

@@ -1,7 +1,7 @@
 package scientifik.kmath.linear
 
 /**
- * A marker interface representing some matrix feature like diagonal, sparce, zero, etc. Features used to optimize matrix
+ * A marker interface representing some matrix feature like diagonal, sparse, zero, etc. Features used to optimize matrix
  * operations performance in some cases.
  */
 interface MatrixFeature
@@ -36,19 +36,19 @@ interface DeterminantFeature<T : Any> : MatrixFeature {
 }
 
 @Suppress("FunctionName")
-fun <T: Any> DeterminantFeature(determinant: T) = object: DeterminantFeature<T>{
+fun <T : Any> DeterminantFeature(determinant: T): DeterminantFeature<T> = object : DeterminantFeature<T> {
     override val determinant: T = determinant
 }
 
 /**
  * Lower triangular matrix
  */
-object LFeature: MatrixFeature
+object LFeature : MatrixFeature
 
 /**
  * Upper triangular feature
  */
-object UFeature: MatrixFeature
+object UFeature : MatrixFeature
 
 /**
  * TODO add documentation

kmath-core/src/commonMain/kotlin/scientifik/kmath/linear/VectorSpace.kt

@@ -2,6 +2,7 @@ package scientifik.kmath.linear
 
 import scientifik.kmath.operations.RealField
 import scientifik.kmath.operations.Space
+import scientifik.kmath.operations.invoke
 import scientifik.kmath.structures.Buffer
 import scientifik.kmath.structures.BufferFactory
 
@@ -10,10 +11,9 @@ import scientifik.kmath.structures.BufferFactory
  * Could be used on any point-like structure
  */
 interface VectorSpace<T : Any, S : Space<T>> : Space<Point<T>> {
-
     val size: Int
-
     val space: S
+    override val zero: Point<T> get() = produce { space.zero }
 
     fun produce(initializer: (Int) -> T): Point<T>
 
@@ -22,30 +22,25 @@ interface VectorSpace<T : Any, S : Space<T>> : Space<Point<T>> {
      */
     //fun produceElement(initializer: (Int) -> T): Vector<T, S>
 
-    override val zero: Point<T> get() = produce { space.zero }
+    override fun add(a: Point<T>, b: Point<T>): Point<T> = produce { space { a[it] + b[it] } }
 
-    override fun add(a: Point<T>, b: Point<T>): Point<T> = produce { with(space) { a[it] + b[it] } }
-
-    override fun multiply(a: Point<T>, k: Number): Point<T> = produce { with(space) { a[it] * k } }
+    override fun multiply(a: Point<T>, k: Number): Point<T> = produce { space { a[it] * k } }
 
     //TODO add basis
 
     companion object {
-
-        private val realSpaceCache = HashMap<Int, BufferVectorSpace<Double, RealField>>()
+        private val realSpaceCache: MutableMap<Int, BufferVectorSpace<Double, RealField>> = hashMapOf()
 
         /**
          * Non-boxing double vector space
          */
-        fun real(size: Int): BufferVectorSpace<Double, RealField> {
-            return realSpaceCache.getOrPut(size) {
+        fun real(size: Int): BufferVectorSpace<Double, RealField> = realSpaceCache.getOrPut(size) {
             BufferVectorSpace(
                 size,
                 RealField,
                 Buffer.Companion::auto
             )
         }
-        }
 
         /**
          * A structured vector space with custom buffer
@@ -54,7 +49,7 @@ interface VectorSpace<T : Any, S : Space<T>> : Space<Point<T>> {
             size: Int,
             space: S,
             bufferFactory: BufferFactory<T> = Buffer.Companion::boxing
-        ) = BufferVectorSpace(size, space, bufferFactory)
+        ): BufferVectorSpace<T, S> = BufferVectorSpace(size, space, bufferFactory)
 
         /**
          * Automatic buffered vector, unboxed if it is possible
@@ -70,6 +65,6 @@ class BufferVectorSpace<T : Any, S : Space<T>>(
     override val space: S,
     val bufferFactory: BufferFactory<T>
 ) : VectorSpace<T, S> {
-    override fun produce(initializer: (Int) -> T) = bufferFactory(size, initializer)
+    override fun produce(initializer: (Int) -> T): Buffer<T> = bufferFactory(size, initializer)
     //override fun produceElement(initializer: (Int) -> T): Vector<T, S> = BufferVector(this, produce(initializer))
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/linear/VirtualMatrix.kt

@@ -18,9 +18,9 @@ class VirtualMatrix<T : Any>(
 
     override val shape: IntArray get() = intArrayOf(rowNum, colNum)
 
-    override fun get(i: Int, j: Int): T = generator(i, j)
+    override operator fun get(i: Int, j: Int): T = generator(i, j)
 
-    override fun suggestFeature(vararg features: MatrixFeature) =
+    override fun suggestFeature(vararg features: MatrixFeature): VirtualMatrix<T> =
         VirtualMatrix(rowNum, colNum, this.features + features, generator)
 
     override fun equals(other: Any?): Boolean {

kmath-core/src/commonMain/kotlin/scientifik/kmath/misc/AutoDiff.kt

@@ -3,8 +3,12 @@ package scientifik.kmath.misc
 import scientifik.kmath.linear.Point
 import scientifik.kmath.operations.ExtendedField
 import scientifik.kmath.operations.Field
+import scientifik.kmath.operations.invoke
 import scientifik.kmath.operations.sum
 import scientifik.kmath.structures.asBuffer
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 
 /*
  * Implementation of backward-mode automatic differentiation.
@@ -22,20 +26,19 @@ class DerivationResult<T : Any>(
     val deriv: Map<Variable<T>, T>,
     val context: Field<T>
 ) : Variable<T>(value) {
-    fun deriv(variable: Variable<T>) = deriv[variable] ?: context.zero
+    fun deriv(variable: Variable<T>): T = deriv[variable] ?: context.zero
 
     /**
      * compute divergence
      */
-    fun div() = context.run { sum(deriv.values) }
+    fun div(): T = context { sum(deriv.values) }
 
     /**
      * Compute a gradient for variables in given order
      */
-    fun grad(vararg variables: Variable<T>): Point<T> = if (variables.isEmpty()) {
-        error("Variable order is not provided for gradient construction")
-    } else {
-        variables.map(::deriv).asBuffer()
+    fun grad(vararg variables: Variable<T>): Point<T> {
+        check(variables.isNotEmpty()) { "Variable order is not provided for gradient construction" }
+        return variables.map(::deriv).asBuffer()
     }
 }
 
@@ -52,19 +55,27 @@ class DerivationResult<T : Any>(
  * assertEquals(9.0, x.d)  // dy/dx
  * ```
  */
-fun <T : Any, F : Field<T>> F.deriv(body: AutoDiffField<T, F>.() -> Variable<T>): DerivationResult<T> =
-    AutoDiffContext<T, F>(this).run {
+inline fun <T : Any, F : Field<T>> F.deriv(body: AutoDiffField<T, F>.() -> Variable<T>): DerivationResult<T> {
+    contract { callsInPlace(body, InvocationKind.EXACTLY_ONCE) }
+
+    return (AutoDiffContext(this)) {
         val result = body()
-        result.d = context.one// computing derivative w.r.t result
+        result.d = context.one // computing derivative w.r.t result
         runBackwardPass()
         DerivationResult(result.value, derivatives, this@deriv)
     }
+}
 
 
 abstract class AutoDiffField<T : Any, F : Field<T>> : Field<Variable<T>> {
-
     abstract val context: F
 
+    /**
+     * A variable accessing inner state of derivatives.
+     * Use this function in inner builders to avoid creating additional derivative bindings
+     */
+    abstract var Variable<T>.d: T
+
     /**
      * Performs update of derivative after the rest of the formula in the back-pass.
      *
@@ -78,15 +89,9 @@ abstract class AutoDiffField<T : Any, F : Field<T>> : Field<Variable<T>> {
      */
     abstract fun <R> derive(value: R, block: F.(R) -> Unit): R
 
-    /**
-     * A variable accessing inner state of derivatives.
-     * Use this function in inner builders to avoid creating additional derivative bindings
-     */
-    abstract var Variable<T>.d: T
-
     abstract fun variable(value: T): Variable<T>
 
-    inline fun variable(block: F.() -> T) = variable(context.block())
+    inline fun variable(block: F.() -> T): Variable<T> = variable(context.block())
 
     // Overloads for Double constants
 
@@ -98,46 +103,35 @@ abstract class AutoDiffField<T : Any, F : Field<T>> : Field<Variable<T>> {
     override operator fun Variable<T>.plus(b: Number): Variable<T> = b.plus(this)
 
     override operator fun Number.minus(b: Variable<T>): Variable<T> =
-        derive(variable { this@minus.toDouble() * one - b.value }) { z ->
-            b.d -= z.d
-        }
+        derive(variable { this@minus.toDouble() * one - b.value }) { z -> b.d -= z.d }
 
     override operator fun Variable<T>.minus(b: Number): Variable<T> =
-        derive(variable { this@minus.value - one * b.toDouble() }) { z ->
-            this@minus.d += z.d
-        }
+        derive(variable { this@minus.value - one * b.toDouble() }) { z -> this@minus.d += z.d }
 }
 
 /**
  * Automatic Differentiation context class.
  */
-private class AutoDiffContext<T : Any, F : Field<T>>(override val context: F) : AutoDiffField<T, F>() {
-
+@PublishedApi
+internal class AutoDiffContext<T : Any, F : Field<T>>(override val context: F) : AutoDiffField<T, F>() {
     // this stack contains pairs of blocks and values to apply them to
-    private var stack = arrayOfNulls<Any?>(8)
-    private var sp = 0
-
-    internal val derivatives = HashMap<Variable<T>, T>()
-
+    private var stack: Array<Any?> = arrayOfNulls<Any?>(8)
+    private var sp: Int = 0
+    val derivatives: MutableMap<Variable<T>, T> = hashMapOf()
+    override val zero: Variable<T> get() = Variable(context.zero)
+    override val one: Variable<T> get() = Variable(context.one)
 
     /**
      * A variable coupled with its derivative. For internal use only
      */
     private class VariableWithDeriv<T : Any>(x: T, var d: T) : Variable<T>(x)
 
-
     override fun variable(value: T): Variable<T> =
         VariableWithDeriv(value, context.zero)
 
     override var Variable<T>.d: T
         get() = (this as? VariableWithDeriv)?.d ?: derivatives[this] ?: context.zero
-        set(value) {
-            if (this is VariableWithDeriv) {
-                d = value
-            } else {
-                derivatives[this] = value
-            }
-        }
+        set(value) = if (this is VariableWithDeriv) d = value else derivatives[this] = value
 
     @Suppress("UNCHECKED_CAST")
     override fun <R> derive(value: R, block: F.(R) -> Unit): R {
@@ -160,67 +154,49 @@ private class AutoDiffContext<T : Any, F : Field<T>>(override val context: F) :
     // Basic math (+, -, *, /)
 
 
-    override fun add(a: Variable<T>, b: Variable<T>): Variable<T> =
-        derive(variable { a.value + b.value }) { z ->
+    override fun add(a: Variable<T>, b: Variable<T>): Variable<T> = derive(variable { a.value + b.value }) { z ->
         a.d += z.d
         b.d += z.d
     }
 
-    override fun multiply(a: Variable<T>, b: Variable<T>): Variable<T> =
-        derive(variable { a.value * b.value }) { z ->
+    override fun multiply(a: Variable<T>, b: Variable<T>): Variable<T> = derive(variable { a.value * b.value }) { z ->
         a.d += z.d * b.value
         b.d += z.d * a.value
     }
 
-    override fun divide(a: Variable<T>, b: Variable<T>): Variable<T> =
-        derive(variable { a.value / b.value }) { z ->
+    override fun divide(a: Variable<T>, b: Variable<T>): Variable<T> = derive(variable { a.value / b.value }) { z ->
         a.d += z.d / b.value
         b.d -= z.d * a.value / (b.value * b.value)
     }
 
-    override fun multiply(a: Variable<T>, k: Number): Variable<T> =
-        derive(variable { k.toDouble() * a.value }) { z ->
+    override fun multiply(a: Variable<T>, k: Number): Variable<T> = derive(variable { k.toDouble() * a.value }) { z ->
         a.d += z.d * k.toDouble()
     }
-
-    override val zero: Variable<T> get() = Variable(context.zero)
-    override val one: Variable<T> get() = Variable(context.one)
 }
 
 // Extensions for differentiation of various basic mathematical functions
 
 // x ^ 2
 fun <T : Any, F : Field<T>> AutoDiffField<T, F>.sqr(x: Variable<T>): Variable<T> =
-    derive(variable { x.value * x.value }) { z ->
-        x.d += z.d * 2 * x.value
-    }
+    derive(variable { x.value * x.value }) { z -> x.d += z.d * 2 * x.value }
 
 // x ^ 1/2
 fun <T : Any, F : ExtendedField<T>> AutoDiffField<T, F>.sqrt(x: Variable<T>): Variable<T> =
-    derive(variable { sqrt(x.value) }) { z ->
-        x.d += z.d * 0.5 / z.value
-    }
+    derive(variable { sqrt(x.value) }) { z -> x.d += z.d * 0.5 / z.value }
 
 // x ^ y (const)
 fun <T : Any, F : ExtendedField<T>> AutoDiffField<T, F>.pow(x: Variable<T>, y: Double): Variable<T> =
-    derive(variable { power(x.value, y) }) { z ->
-        x.d += z.d * y * power(x.value, y - 1)
-    }
+    derive(variable { power(x.value, y) }) { z -> x.d += z.d * y * power(x.value, y - 1) }
 
 fun <T : Any, F : ExtendedField<T>> AutoDiffField<T, F>.pow(x: Variable<T>, y: Int): Variable<T> = pow(x, y.toDouble())
 
 // exp(x)
 fun <T : Any, F : ExtendedField<T>> AutoDiffField<T, F>.exp(x: Variable<T>): Variable<T> =
-    derive(variable { exp(x.value) }) { z ->
-        x.d += z.d * z.value
-    }
+    derive(variable { exp(x.value) }) { z -> x.d += z.d * z.value }
 
 // ln(x)
-fun <T : Any, F : ExtendedField<T>> AutoDiffField<T, F>.ln(x: Variable<T>): Variable<T> = derive(
-    variable { ln(x.value) }
-) { z ->
-    x.d += z.d / x.value
-}
+fun <T : Any, F : ExtendedField<T>> AutoDiffField<T, F>.ln(x: Variable<T>): Variable<T> =
+    derive(variable { ln(x.value) }) { z -> x.d += z.d / x.value }
 
 // x ^ y (any)
 fun <T : Any, F : ExtendedField<T>> AutoDiffField<T, F>.pow(x: Variable<T>, y: Variable<T>): Variable<T> =
@@ -228,12 +204,8 @@ fun <T : Any, F : ExtendedField<T>> AutoDiffField<T, F>.pow(x: Variable<T>, y: V
 
 // sin(x)
 fun <T : Any, F : ExtendedField<T>> AutoDiffField<T, F>.sin(x: Variable<T>): Variable<T> =
-    derive(variable { sin(x.value) }) { z ->
-        x.d += z.d * cos(x.value)
-    }
+    derive(variable { sin(x.value) }) { z -> x.d += z.d * cos(x.value) }
 
 // cos(x)
 fun <T : Any, F : ExtendedField<T>> AutoDiffField<T, F>.cos(x: Variable<T>): Variable<T> =
-    derive(variable { cos(x.value) }) { z ->
-        x.d -= z.d * sin(x.value)
-    }
+    derive(variable { cos(x.value) }) { z -> x.d -= z.d * sin(x.value) }

kmath-core/src/commonMain/kotlin/scientifik/kmath/misc/Grids.kt

@@ -41,6 +41,6 @@ fun ClosedFloatingPointRange<Double>.toSequenceWithPoints(numPoints: Int): Seque
  */
 @Deprecated("Replace by 'toSequenceWithPoints'")
 fun ClosedFloatingPointRange<Double>.toGrid(numPoints: Int): DoubleArray {
-    if (numPoints < 2) error("Can't create generic grid with less than two points")
+    require(numPoints >= 2) { "Can't create generic grid with less than two points" }
     return DoubleArray(numPoints) { i -> start + (endInclusive - start) / (numPoints - 1) * i }
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/misc/cumulative.kt

@@ -1,76 +1,80 @@
 package scientifik.kmath.misc
 
 import scientifik.kmath.operations.Space
+import scientifik.kmath.operations.invoke
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 import kotlin.jvm.JvmName
 
-
 /**
- * Generic cumulative operation on iterator
- * @param T type of initial iterable
- * @param R type of resulting iterable
- * @param initial lazy evaluated
+ * Generic cumulative operation on iterator.
+ *
+ * @param T the type of initial iterable.
+ * @param R the type of resulting iterable.
+ * @param initial lazy evaluated.
  */
-fun <T, R> Iterator<T>.cumulative(initial: R, operation: (R, T) -> R): Iterator<R> = object : Iterator<R> {
+inline fun <T, R> Iterator<T>.cumulative(initial: R, crossinline operation: (R, T) -> R): Iterator<R> {
+    contract { callsInPlace(operation) }
+
+    return object : Iterator<R> {
         var state: R = initial
+
         override fun hasNext(): Boolean = this@cumulative.hasNext()
 
         override fun next(): R {
             state = operation(state, this@cumulative.next())
             return state
         }
+    }
 }
 
-fun <T, R> Iterable<T>.cumulative(initial: R, operation: (R, T) -> R): Iterable<R> = object : Iterable<R> {
-    override fun iterator(): Iterator<R> = this@cumulative.iterator().cumulative(initial, operation)
-}
+inline fun <T, R> Iterable<T>.cumulative(initial: R, crossinline operation: (R, T) -> R): Iterable<R> =
+    Iterable { this@cumulative.iterator().cumulative(initial, operation) }
 
-fun <T, R> Sequence<T>.cumulative(initial: R, operation: (R, T) -> R): Sequence<R> = object : Sequence<R> {
-    override fun iterator(): Iterator<R> = this@cumulative.iterator().cumulative(initial, operation)
+inline fun <T, R> Sequence<T>.cumulative(initial: R, crossinline operation: (R, T) -> R): Sequence<R> = Sequence {
+    this@cumulative.iterator().cumulative(initial, operation)
 }
 
 fun <T, R> List<T>.cumulative(initial: R, operation: (R, T) -> R): List<R> =
-    this.iterator().cumulative(initial, operation).asSequence().toList()
+    iterator().cumulative(initial, operation).asSequence().toList()
 
 //Cumulative sum
 
 /**
  * Cumulative sum with custom space
  */
-fun <T> Iterable<T>.cumulativeSum(space: Space<T>) = with(space) {
-    cumulative(zero) { element: T, sum: T -> sum + element }
-}
+fun <T> Iterable<T>.cumulativeSum(space: Space<T>): Iterable<T> =
+    space { cumulative(zero) { element: T, sum: T -> sum + element } }
 
 @JvmName("cumulativeSumOfDouble")
-fun Iterable<Double>.cumulativeSum() = this.cumulative(0.0) { element, sum -> sum + element }
+fun Iterable<Double>.cumulativeSum(): Iterable<Double> = cumulative(0.0) { element, sum -> sum + element }
 
 @JvmName("cumulativeSumOfInt")
-fun Iterable<Int>.cumulativeSum() = this.cumulative(0) { element, sum -> sum + element }
+fun Iterable<Int>.cumulativeSum(): Iterable<Int> = cumulative(0) { element, sum -> sum + element }
 
 @JvmName("cumulativeSumOfLong")
-fun Iterable<Long>.cumulativeSum() = this.cumulative(0L) { element, sum -> sum + element }
+fun Iterable<Long>.cumulativeSum(): Iterable<Long> = cumulative(0L) { element, sum -> sum + element }
 
-fun <T> Sequence<T>.cumulativeSum(space: Space<T>) = with(space) {
-    cumulative(zero) { element: T, sum: T -> sum + element }
-}
+fun <T> Sequence<T>.cumulativeSum(space: Space<T>): Sequence<T> =
+    space { cumulative(zero) { element: T, sum: T -> sum + element } }
 
 @JvmName("cumulativeSumOfDouble")
-fun Sequence<Double>.cumulativeSum() = this.cumulative(0.0) { element, sum -> sum + element }
+fun Sequence<Double>.cumulativeSum(): Sequence<Double> = cumulative(0.0) { element, sum -> sum + element }
 
 @JvmName("cumulativeSumOfInt")
-fun Sequence<Int>.cumulativeSum() = this.cumulative(0) { element, sum -> sum + element }
+fun Sequence<Int>.cumulativeSum(): Sequence<Int> = cumulative(0) { element, sum -> sum + element }
 
 @JvmName("cumulativeSumOfLong")
-fun Sequence<Long>.cumulativeSum() = this.cumulative(0L) { element, sum -> sum + element }
+fun Sequence<Long>.cumulativeSum(): Sequence<Long> = cumulative(0L) { element, sum -> sum + element }
 
-fun <T> List<T>.cumulativeSum(space: Space<T>) = with(space) {
-    cumulative(zero) { element: T, sum: T -> sum + element }
-}
+fun <T> List<T>.cumulativeSum(space: Space<T>): List<T> =
+    space { cumulative(zero) { element: T, sum: T -> sum + element } }
 
 @JvmName("cumulativeSumOfDouble")
-fun List<Double>.cumulativeSum() = this.cumulative(0.0) { element, sum -> sum + element }
+fun List<Double>.cumulativeSum(): List<Double> = cumulative(0.0) { element, sum -> sum + element }
 
 @JvmName("cumulativeSumOfInt")
-fun List<Int>.cumulativeSum() = this.cumulative(0) { element, sum -> sum + element }
+fun List<Int>.cumulativeSum(): List<Int> = cumulative(0) { element, sum -> sum + element }
 
 @JvmName("cumulativeSumOfLong")
-fun List<Long>.cumulativeSum() = this.cumulative(0L) { element, sum -> sum + element }
+fun List<Long>.cumulativeSum(): List<Long> = cumulative(0L) { element, sum -> sum + element }

kmath-core/src/commonMain/kotlin/scientifik/kmath/operations/Algebra.kt

@@ -1,10 +1,15 @@
 package scientifik.kmath.operations
 
+/**
+ * Stub for DSL the [Algebra] is.
+ */
 @DslMarker
 annotation class KMathContext
 
 /**
- * Marker interface for any algebra
+ * Represents an algebraic structure.
+ *
+ * @param T the type of element of this structure.
  */
 interface Algebra<T> {
     /**
@@ -24,50 +29,121 @@ interface Algebra<T> {
 }
 
 /**
- * An algebra with numeric representation of members
+ * An algebraic structure where elements can have numeric representation.
+ *
+ * @param T the type of element of this structure.
  */
 interface NumericAlgebra<T> : Algebra<T> {
     /**
-     * Wrap a number
+     * Wraps a number.
      */
     fun number(value: Number): T
 
+    /**
+     * Dynamic call of binary operation [operation] on [left] and [right] where left element is [Number].
+     */
     fun leftSideNumberOperation(operation: String, left: Number, right: T): T =
         binaryOperation(operation, number(left), right)
 
+    /**
+     * Dynamic call of binary operation [operation] on [left] and [right] where right element is [Number].
+     */
     fun rightSideNumberOperation(operation: String, left: T, right: Number): T =
         leftSideNumberOperation(operation, right, left)
 }
 
 /**
- * Call a block with an [Algebra] as receiver
+ * Call a block with an [Algebra] as receiver.
  */
 inline operator fun <A : Algebra<*>, R> A.invoke(block: A.() -> R): R = run(block)
 
 /**
- * Space-like operations without neutral element
+ * Represents "semispace", i.e. algebraic structure with associative binary operation called "addition" as well as
+ * multiplication by scalars.
+ *
+ * @param T the type of element of this semispace.
  */
 interface SpaceOperations<T> : Algebra<T> {
     /**
-     * Addition operation for two context elements
+     * Addition of two elements.
+     *
+     * @param a the addend.
+     * @param b the augend.
+     * @return the sum.
      */
     fun add(a: T, b: T): T
 
     /**
-     * Multiplication operation for context element and real number
+     * Multiplication of element by scalar.
+     *
+     * @param a the multiplier.
+     * @param k the multiplicand.
+     * @return the produce.
      */
     fun multiply(a: T, k: Number): T
 
-    //Operation to be performed in this context. Could be moved to extensions in case of KEEP-176
+    // Operations to be performed in this context. Could be moved to extensions in case of KEEP-176
+
+    /**
+     * The negation of this element.
+     *
+     * @receiver this value.
+     * @return the additive inverse of this value.
+     */
     operator fun T.unaryMinus(): T = multiply(this, -1.0)
 
+    /**
+     * Returns this value.
+     *
+     * @receiver this value.
+     * @return this value.
+     */
     operator fun T.unaryPlus(): T = this
 
+    /**
+     * Addition of two elements.
+     *
+     * @receiver the addend.
+     * @param b the augend.
+     * @return the sum.
+     */
     operator fun T.plus(b: T): T = add(this, b)
+
+    /**
+     * Subtraction of two elements.
+     *
+     * @receiver the minuend.
+     * @param b the subtrahend.
+     * @return the difference.
+     */
     operator fun T.minus(b: T): T = add(this, -b)
-    operator fun T.times(k: Number) = multiply(this, k.toDouble())
-    operator fun T.div(k: Number) = multiply(this, 1.0 / k.toDouble())
-    operator fun Number.times(b: T) = b * this
+
+    /**
+     * Multiplication of this element by a scalar.
+     *
+     * @receiver the multiplier.
+     * @param k the multiplicand.
+     * @return the product.
+     */
+    operator fun T.times(k: Number): T = multiply(this, k.toDouble())
+
+    /**
+     * Division of this element by scalar.
+     *
+     * @receiver the dividend.
+     * @param k the divisor.
+     * @return the quotient.
+     */
+    operator fun T.div(k: Number): T = multiply(this, 1.0 / k.toDouble())
+
+    /**
+     * Multiplication of this number by element.
+     *
+     * @receiver the multiplier.
+     * @param b the multiplicand.
+     * @return the product.
+     */
+    operator fun Number.times(b: T): T = b * this
 
     override fun unaryOperation(operation: String, arg: T): T = when (operation) {
         PLUS_OPERATION -> arg
@@ -82,37 +158,54 @@ interface SpaceOperations<T> : Algebra<T> {
     }
 
     companion object {
-        const val PLUS_OPERATION = "+"
-        const val MINUS_OPERATION = "-"
-        const val NOT_OPERATION = "!"
+        /**
+         * The identifier of addition.
+         */
+        const val PLUS_OPERATION: String = "+"
+
+        /**
+         * The identifier of subtraction (and negation).
+         */
+        const val MINUS_OPERATION: String = "-"
+
+        const val NOT_OPERATION: String = "!"
     }
 }
 
-
 /**
- * A general interface representing linear context of some kind.
- * The context defines sum operation for its elements and multiplication by real value.
- * One must note that in some cases context is a singleton class, but in some cases it
- * works as a context for operations inside it.
+ * Represents linear space, i.e. algebraic structure with associative binary operation called "addition" and its neutral
+ * element as well as multiplication by scalars.
  *
- * TODO do we need non-commutative context?
+ * @param T the type of element of this group.
  */
 interface Space<T> : SpaceOperations<T> {
     /**
-     * Neutral element for sum operation
+     * The neutral element of addition.
      */
     val zero: T
 }
 
 /**
- * Operations on ring without multiplication neutral element
+ * Represents semiring, i.e. algebraic structure with two associative binary operations called "addition" and
+ * "multiplication".
+ *
+ * @param T the type of element of this semiring.
  */
 interface RingOperations<T> : SpaceOperations<T> {
     /**
-     * Multiplication for two field elements
+     * Multiplies two elements.
+     *
+     * @param a the multiplier.
+     * @param b the multiplicand.
      */
     fun multiply(a: T, b: T): T
 
+    /**
+     * Multiplies this element by scalar.
+     *
+     * @receiver the multiplier.
+     * @param b the multiplicand.
+     */
     operator fun T.times(b: T): T = multiply(this, b)
 
     override fun binaryOperation(operation: String, left: T, right: T): T = when (operation) {
@@ -121,12 +214,18 @@ interface RingOperations<T> : SpaceOperations<T> {
     }
 
     companion object {
-        const val TIMES_OPERATION = "*"
+        /**
+         * The identifier of multiplication.
+         */
+        const val TIMES_OPERATION: String = "*"
     }
 }
 
 /**
- * The same as {@link Space} but with additional multiplication operation
+ * Represents ring, i.e. algebraic structure with two associative binary operations called "addition" and
+ * "multiplication" and their neutral elements.
+ *
+ * @param T the type of element of this ring.
  */
 interface Ring<T> : Space<T>, RingOperations<T>, NumericAlgebra<T> {
     /**
@@ -150,20 +249,64 @@ interface Ring<T> : Space<T>, RingOperations<T>, NumericAlgebra<T> {
         else -> super.rightSideNumberOperation(operation, left, right)
     }
 
+    /**
+     * Addition of element and scalar.
+     *
+     * @receiver the addend.
+     * @param b the augend.
+     */
+    operator fun T.plus(b: Number): T = this + number(b)
 
-    operator fun T.plus(b: Number) = this.plus(number(b))
-    operator fun Number.plus(b: T) = b + this
+    /**
+     * Addition of scalar and element.
+     *
+     * @receiver the addend.
+     * @param b the augend.
+     */
+    operator fun Number.plus(b: T): T = b + this
 
-    operator fun T.minus(b: Number) = this.minus(number(b))
-    operator fun Number.minus(b: T) = -b + this
+    /**
+     * Subtraction of element from number.
+     *
+     * @receiver the minuend.
+     * @param b the subtrahend.
+     * @receiver the difference.
+     */
+    operator fun T.minus(b: Number): T = this - number(b)
+
+    /**
+     * Subtraction of number from element.
+     *
+     * @receiver the minuend.
+     * @param b the subtrahend.
+     * @receiver the difference.
+     */
+    operator fun Number.minus(b: T): T = -b + this
 }
 
 /**
- * All ring operations but without neutral elements
+ * Represents semifield, i.e. algebraic structure with three operations: associative "addition" and "multiplication",
+ * and "division".
+ *
+ * @param T the type of element of this semifield.
  */
 interface FieldOperations<T> : RingOperations<T> {
+    /**
+     * Division of two elements.
+     *
+     * @param a the dividend.
+     * @param b the divisor.
+     * @return the quotient.
+     */
     fun divide(a: T, b: T): T
 
+    /**
+     * Division of two elements.
+     *
+     * @receiver the dividend.
+     * @param b the divisor.
+     * @return the quotient.
+     */
     operator fun T.div(b: T): T = divide(this, b)
 
     override fun binaryOperation(operation: String, left: T, right: T): T = when (operation) {
@@ -172,13 +315,26 @@ interface FieldOperations<T> : RingOperations<T> {
     }
 
     companion object {
-        const val DIV_OPERATION = "/"
+        /**
+         * The identifier of division.
+         */
+        const val DIV_OPERATION: String = "/"
     }
 }
 
 /**
- * Four operations algebra
+ * Represents field, i.e. algebraic structure with three operations: associative "addition" and "multiplication",
+ * and "division" and their neutral elements.
+ *
+ * @param T the type of element of this semifield.
  */
 interface Field<T> : Ring<T>, FieldOperations<T> {
-    operator fun Number.div(b: T) = this * divide(one, b)
+    /**
+     * Division of element by scalar.
+     *
+     * @receiver the dividend.
+     * @param b the divisor.
+     * @return the quotient.
+     */
+    operator fun Number.div(b: T): T = this * divide(one, b)
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/operations/AlgebraElements.kt

@@ -2,47 +2,107 @@ package scientifik.kmath.operations
 
 /**
  * The generic mathematics elements which is able to store its context
- * @param T the type of space operation results
- * @param I self type of the element. Needed for static type checking
- * @param C the type of mathematical context for this element
+ *
+ * @param C the type of mathematical context for this element.
  */
 interface MathElement<C> {
     /**
-     * The context this element belongs to
+     * The context this element belongs to.
      */
     val context: C
 }
 
+/**
+ * Represents element that can be wrapped to its "primitive" value.
+ *
+ * @param T the type wrapped by this wrapper.
+ * @param I the type of this wrapper.
+ */
 interface MathWrapper<T, I> {
+    /**
+     * Unwraps [I] to [T].
+     */
     fun unwrap(): T
+
+    /**
+     * Wraps [T] to [I].
+     */
     fun T.wrap(): I
 }
 
 /**
- * The element of linear context
- * @param T the type of space operation results
- * @param I self type of the element. Needed for static type checking
- * @param S the type of space
+ * The element of [Space].
+ *
+ * @param T the type of space operation results.
+ * @param I self type of the element. Needed for static type checking.
+ * @param S the type of space.
  */
 interface SpaceElement<T, I : SpaceElement<T, I, S>, S : Space<T>> : MathElement<S>, MathWrapper<T, I> {
+    /**
+     * Adds element to this one.
+     *
+     * @param b the augend.
+     * @return the sum.
+     */
+    operator fun plus(b: T): I = context.add(unwrap(), b).wrap()
 
-    operator fun plus(b: T) = context.add(unwrap(), b).wrap()
-    operator fun minus(b: T) = context.add(unwrap(), context.multiply(b, -1.0)).wrap()
-    operator fun times(k: Number) = context.multiply(unwrap(), k.toDouble()).wrap()
-    operator fun div(k: Number) = context.multiply(unwrap(), 1.0 / k.toDouble()).wrap()
+    /**
+     * Subtracts element from this one.
+     *
+     * @param b the subtrahend.
+     * @return the difference.
+     */
+    operator fun minus(b: T): I = context.add(unwrap(), context.multiply(b, -1.0)).wrap()
+
+    /**
+     * Multiplies this element by number.
+     *
+     * @param k the multiplicand.
+     * @return the product.
+     */
+    operator fun times(k: Number): I = context.multiply(unwrap(), k.toDouble()).wrap()
+
+    /**
+     * Divides this element by number.
+     *
+     * @param k the divisor.
+     * @return the quotient.
+     */
+    operator fun div(k: Number): I = context.multiply(unwrap(), 1.0 / k.toDouble()).wrap()
 }
 
 /**
- * Ring element
+ * The element of [Ring].
+ *
+ * @param T the type of space operation results.
+ * @param I self type of the element. Needed for static type checking.
+ * @param R the type of space.
  */
 interface RingElement<T, I : RingElement<T, I, R>, R : Ring<T>> : SpaceElement<T, I, R> {
-    operator fun times(b: T) = context.multiply(unwrap(), b).wrap()
+    /**
+     * Multiplies this element by another one.
+     *
+     * @param b the multiplicand.
+     * @return the product.
+     */
+    operator fun times(b: T): I = context.multiply(unwrap(), b).wrap()
 }
 
 /**
- * Field element
+ * The element of [Field].
+ *
+ * @param T the type of space operation results.
+ * @param I self type of the element. Needed for static type checking.
+ * @param F the type of field.
  */
 interface FieldElement<T, I : FieldElement<T, I, F>, F : Field<T>> : RingElement<T, I, F> {
     override val context: F
-    operator fun div(b: T) = context.divide(unwrap(), b).wrap()
+
+    /**
+     * Divides this element by another one.
+     *
+     * @param b the divisor.
+     * @return the quotient.
+     */
+    operator fun div(b: T): I = context.divide(unwrap(), b).wrap()
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/operations/AlgebraExtensions.kt

@@ -1,15 +1,107 @@
 package scientifik.kmath.operations
 
+/**
+ * Returns the sum of all elements in the iterable in this [Space].
+ *
+ * @receiver the algebra that provides addition.
+ * @param data the iterable to sum up.
+ * @return the sum.
+ */
 fun <T> Space<T>.sum(data: Iterable<T>): T = data.fold(zero) { left, right -> add(left, right) }
+
+/**
+ * Returns the sum of all elements in the sequence in this [Space].
+ *
+ * @receiver the algebra that provides addition.
+ * @param data the sequence to sum up.
+ * @return the sum.
+ */
 fun <T> Space<T>.sum(data: Sequence<T>): T = data.fold(zero) { left, right -> add(left, right) }
 
-fun <T : Any, S : Space<T>> Iterable<T>.sumWith(space: S): T = space.sum(this)
+/**
+ * Returns an average value of elements in the iterable in this [Space].
+ *
+ * @receiver the algebra that provides addition and division.
+ * @param data the iterable to find average.
+ * @return the average value.
+ */
+fun <T> Space<T>.average(data: Iterable<T>): T = sum(data) / data.count()
+
+/**
+ * Returns an average value of elements in the sequence in this [Space].
+ *
+ * @receiver the algebra that provides addition and division.
+ * @param data the sequence to find average.
+ * @return the average value.
+ */
+fun <T> Space<T>.average(data: Sequence<T>): T = sum(data) / data.count()
+
+/**
+ * Returns the sum of all elements in the iterable in provided space.
+ *
+ * @receiver the collection to sum up.
+ * @param space the algebra that provides addition.
+ * @return the sum.
+ */
+fun <T> Iterable<T>.sumWith(space: Space<T>): T = space.sum(this)
+
+/**
+ * Returns the sum of all elements in the sequence in provided space.
+ *
+ * @receiver the collection to sum up.
+ * @param space the algebra that provides addition.
+ * @return the sum.
+ */
+fun <T> Sequence<T>.sumWith(space: Space<T>): T = space.sum(this)
+
+/**
+ * Returns an average value of elements in the iterable in this [Space].
+ *
+ * @receiver the iterable to find average.
+ * @param space the algebra that provides addition and division.
+ * @return the average value.
+ */
+fun <T> Iterable<T>.averageWith(space: Space<T>): T = space.average(this)
+
+/**
+ * Returns an average value of elements in the sequence in this [Space].
+ *
+ * @receiver the sequence to find average.
+ * @param space the algebra that provides addition and division.
+ * @return the average value.
+ */
+fun <T> Sequence<T>.averageWith(space: Space<T>): T = space.average(this)
 
 //TODO optimized power operation
-fun <T> RingOperations<T>.power(arg: T, power: Int): T {
+
+/**
+ * Raises [arg] to the natural power [power].
+ *
+ * @receiver the algebra to provide multiplication.
+ * @param arg the base.
+ * @param power the exponent.
+ * @return the base raised to the power.
+ */
+fun <T> Ring<T>.power(arg: T, power: Int): T {
+    require(power >= 0) { "The power can't be negative." }
+    require(power != 0 || arg != zero) { "The $zero raised to $power is not defined." }
+    if (power == 0) return one
     var res = arg
-    repeat(power - 1) {
-        res *= arg
-    }
+    repeat(power - 1) { res *= arg }
     return res
 }
+
+/**
+ * Raises [arg] to the integer power [power].
+ *
+ * @receiver the algebra to provide multiplication and division.
+ * @param arg the base.
+ * @param power the exponent.
+ * @return the base raised to the power.
+ */
+fun <T> Field<T>.power(arg: T, power: Int): T {
+    require(power != 0 || arg != zero) { "The $zero raised to $power is not defined." }
+    if (power == 0) return one
+    if (power < 0) return one / (this as Ring<T>).power(arg, -power)
+    return (this as Ring<T>).power(arg, power)
+}

kmath-core/src/commonMain/kotlin/scientifik/kmath/operations/BigInt.kt

@@ -3,12 +3,13 @@ package scientifik.kmath.operations
 import scientifik.kmath.operations.BigInt.Companion.BASE
 import scientifik.kmath.operations.BigInt.Companion.BASE_SIZE
 import scientifik.kmath.structures.*
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 import kotlin.math.log2
 import kotlin.math.max
 import kotlin.math.min
 import kotlin.math.sign
 
-
 typealias Magnitude = UIntArray
 typealias TBase = ULong
 
@@ -22,8 +23,9 @@ object BigIntField : Field<BigInt> {
     override val one: BigInt = BigInt.ONE
 
     override fun add(a: BigInt, b: BigInt): BigInt = a.plus(b)
+    override fun number(value: Number): BigInt = value.toLong().toBigInt()
 
-    override fun multiply(a: BigInt, k: Number): BigInt = a.times(k.toLong())
+    override fun multiply(a: BigInt, k: Number): BigInt = a.times(number(k))
 
     override fun multiply(a: BigInt, b: BigInt): BigInt = a.times(b)
 
@@ -194,8 +196,8 @@ class BigInt internal constructor(
     }
 
     infix fun or(other: BigInt): BigInt {
-        if (this == ZERO) return other;
-        if (other == ZERO) return this;
+        if (this == ZERO) return other
+        if (other == ZERO) return this
         val resSize = max(this.magnitude.size, other.magnitude.size)
         val newMagnitude: Magnitude = Magnitude(resSize)
         for (i in 0 until resSize) {
@@ -210,7 +212,7 @@ class BigInt internal constructor(
     }
 
     infix fun and(other: BigInt): BigInt {
-        if ((this == ZERO) or (other == ZERO)) return ZERO;
+        if ((this == ZERO) or (other == ZERO)) return ZERO
         val resSize = min(this.magnitude.size, other.magnitude.size)
         val newMagnitude: Magnitude = Magnitude(resSize)
         for (i in 0 until resSize) {
@@ -260,7 +262,7 @@ class BigInt internal constructor(
     }
 
     companion object {
-        const val BASE = 0xffffffffUL
+        const val BASE: ULong = 0xffffffffUL
         const val BASE_SIZE: Int = 32
         val ZERO: BigInt = BigInt(0, uintArrayOf())
         val ONE: BigInt = BigInt(1, uintArrayOf(1u))
@@ -394,12 +396,12 @@ fun abs(x: BigInt): BigInt = x.abs()
 /**
  * Convert this [Int] to [BigInt]
  */
-fun Int.toBigInt() = BigInt(sign.toByte(), uintArrayOf(kotlin.math.abs(this).toUInt()))
+fun Int.toBigInt(): BigInt = BigInt(sign.toByte(), uintArrayOf(kotlin.math.abs(this).toUInt()))
 
 /**
  * Convert this [Long] to [BigInt]
  */
-fun Long.toBigInt() = BigInt(
+fun Long.toBigInt(): BigInt = BigInt(
     sign.toByte(), stripLeadingZeros(
         uintArrayOf(
             (kotlin.math.abs(this).toULong() and BASE).toUInt(),
@@ -411,17 +413,17 @@ fun Long.toBigInt() = BigInt(
 /**
  * Convert UInt to [BigInt]
  */
-fun UInt.toBigInt() = BigInt(1, uintArrayOf(this))
+fun UInt.toBigInt(): BigInt = BigInt(1, uintArrayOf(this))
 
 /**
  * Convert ULong to [BigInt]
  */
-fun ULong.toBigInt() = BigInt(
+fun ULong.toBigInt(): BigInt = BigInt(
     1,
     stripLeadingZeros(
         uintArrayOf(
-            (this and BigInt.BASE).toUInt(),
-            ((this shr BigInt.BASE_SIZE) and BigInt.BASE).toUInt()
+            (this and BASE).toUInt(),
+            ((this shr BASE_SIZE) and BASE).toUInt()
         )
     )
 )
@@ -430,11 +432,11 @@ fun ULong.toBigInt() = BigInt(
  * Create a [BigInt] with this array of magnitudes with protective copy
  */
 fun UIntArray.toBigInt(sign: Byte): BigInt {
-    if (sign == 0.toByte() && isNotEmpty()) error("")
-    return BigInt(sign, this.copyOf())
+    require(sign != 0.toByte() || !isNotEmpty())
+    return BigInt(sign, copyOf())
 }
 
-val hexChToInt = hashMapOf(
+val hexChToInt: MutableMap<Char, Int> = hashMapOf(
     '0' to 0, '1' to 1, '2' to 2, '3' to 3,
     '4' to 4, '5' to 5, '6' to 6, '7' to 7,
     '8' to 8, '9' to 9, 'A' to 10, 'B' to 11,
@@ -484,11 +486,15 @@ fun String.parseBigInteger(): BigInt? {
     return res * sign
 }
 
-inline fun Buffer.Companion.bigInt(size: Int, initializer: (Int) -> BigInt): Buffer<BigInt> =
-    boxing(size, initializer)
+inline fun Buffer.Companion.bigInt(size: Int, initializer: (Int) -> BigInt): Buffer<BigInt> {
+    contract { callsInPlace(initializer) }
+    return boxing(size, initializer)
+}
 
-inline fun MutableBuffer.Companion.bigInt(size: Int, initializer: (Int) -> BigInt): MutableBuffer<BigInt> =
-    boxing(size, initializer)
+inline fun MutableBuffer.Companion.bigInt(size: Int, initializer: (Int) -> BigInt): MutableBuffer<BigInt> {
+    contract { callsInPlace(initializer) }
+    return boxing(size, initializer)
+}
 
 fun NDAlgebra.Companion.bigInt(vararg shape: Int): BoxingNDRing<BigInt, BigIntField> =
     BoxingNDRing(shape, BigIntField, Buffer.Companion::bigInt)
@@ -496,5 +502,4 @@ fun NDAlgebra.Companion.bigInt(vararg shape: Int): BoxingNDRing<BigInt, BigIntFi
 fun NDElement.Companion.bigInt(
     vararg shape: Int,
     initializer: BigIntField.(IntArray) -> BigInt
-): BufferedNDRingElement<BigInt, BigIntField> =
-    NDAlgebra.bigInt(*shape).produce(initializer)
+): BufferedNDRingElement<BigInt, BigIntField> = NDAlgebra.bigInt(*shape).produce(initializer)

kmath-core/src/commonMain/kotlin/scientifik/kmath/operations/Complex.kt

@@ -6,19 +6,50 @@ import scientifik.kmath.structures.MutableBuffer
 import scientifik.memory.MemoryReader
 import scientifik.memory.MemorySpec
 import scientifik.memory.MemoryWriter
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 import kotlin.math.*
 
+/**
+ * This complex's conjugate.
+ */
+val Complex.conjugate: Complex
+    get() = Complex(re, -im)
+
+/**
+ * This complex's reciprocal.
+ */
+val Complex.reciprocal: Complex
+    get() {
+        val scale = re * re + im * im
+        return Complex(re / scale, -im / scale)
+    }
+
+/**
+ * Absolute value of complex number.
+ */
+val Complex.r: Double
+    get() = sqrt(re * re + im * im)
+
+/**
+ * An angle between vector represented by complex number and X axis.
+ */
+val Complex.theta: Double
+    get() = atan(im / re)
+
 private val PI_DIV_2 = Complex(PI / 2, 0)
 
 /**
- * A field for complex numbers
+ * A field of [Complex].
  */
-object ComplexField : ExtendedField<Complex> {
-    override val zero: Complex = Complex(0.0, 0.0)
+object ComplexField : ExtendedField<Complex>, Norm<Complex, Complex> {
+    override val zero: Complex = 0.0.toComplex()
+    override val one: Complex = 1.0.toComplex()
 
-    override val one: Complex = Complex(1.0, 0.0)
-
-    val i = Complex(0.0, 1.0)
+    /**
+     * The imaginary unit.
+     */
+    val i: Complex = Complex(0.0, 1.0)
 
     override fun add(a: Complex, b: Complex): Complex = Complex(a.re + b.re, a.im + b.im)
 
@@ -27,53 +58,123 @@ object ComplexField : ExtendedField<Complex> {
     override fun multiply(a: Complex, b: Complex): Complex =
         Complex(a.re * b.re - a.im * b.im, a.re * b.im + a.im * b.re)
 
-    override fun divide(a: Complex, b: Complex): Complex {
-        val norm = b.re * b.re + b.im * b.im
-        return Complex((a.re * b.re + a.im * b.im) / norm, (a.re * b.im - a.im * b.re) / norm)
+    override fun divide(a: Complex, b: Complex): Complex = when {
+        b.re.isNaN() || b.im.isNaN() -> Complex(Double.NaN, Double.NaN)
+
+        (if (b.im < 0) -b.im else +b.im) < (if (b.re < 0) -b.re else +b.re) -> {
+            val wr = b.im / b.re
+            val wd = b.re + wr * b.im
+
+            if (wd.isNaN() || wd == 0.0)
+                Complex(Double.NaN, Double.NaN)
+            else
+                Complex((a.re + a.im * wr) / wd, (a.im - a.re * wr) / wd)
+        }
+
+        b.im == 0.0 -> Complex(Double.NaN, Double.NaN)
+
+        else -> {
+            val wr = b.re / b.im
+            val wd = b.im + wr * b.re
+
+            if (wd.isNaN() || wd == 0.0)
+                Complex(Double.NaN, Double.NaN)
+            else
+                Complex((a.re * wr + a.im) / wd, (a.im * wr - a.re) / wd)
+        }
     }
 
     override fun sin(arg: Complex): Complex = i * (exp(-i * arg) - exp(i * arg)) / 2
     override fun cos(arg: Complex): Complex = (exp(-i * arg) + exp(i * arg)) / 2
-    override fun asin(arg: Complex): Complex = -i * ln(sqrt(one - arg pow 2) + i * arg)
-    override fun acos(arg: Complex): Complex = PI_DIV_2 + i * ln(sqrt(one - arg pow 2) + i * arg)
-    override fun atan(arg: Complex): Complex = i * (ln(one - i * arg) - ln(one + i * arg)) / 2
 
-    override fun power(arg: Complex, pow: Number): Complex =
-        arg.r.pow(pow.toDouble()) * (cos(pow.toDouble() * arg.theta) + i * sin(pow.toDouble() * arg.theta))
+    override fun tan(arg: Complex): Complex {
+        val e1 = exp(-i * arg)
+        val e2 = exp(i * arg)
+        return i * (e1 - e2) / (e1 + e2)
+    }
+
+    override fun asin(arg: Complex): Complex = -i * ln(sqrt(1 - (arg * arg)) + i * arg)
+    override fun acos(arg: Complex): Complex = PI_DIV_2 + i * ln(sqrt(1 - (arg * arg)) + i * arg)
+
+    override fun atan(arg: Complex): Complex {
+        val iArg = i * arg
+        return i * (ln(1 - iArg) - ln(1 + iArg)) / 2
+    }
+
+    override fun power(arg: Complex, pow: Number): Complex = if (arg.im == 0.0)
+        arg.re.pow(pow.toDouble()).toComplex()
+    else
+        exp(pow * ln(arg))
 
     override fun exp(arg: Complex): Complex = exp(arg.re) * (cos(arg.im) + i * sin(arg.im))
 
     override fun ln(arg: Complex): Complex = ln(arg.r) + i * atan2(arg.im, arg.re)
 
-    operator fun Double.plus(c: Complex) = add(this.toComplex(), c)
+    /**
+     * Adds complex number to real one.
+     *
+     * @receiver the addend.
+     * @param c the augend.
+     * @return the sum.
+     */
+    operator fun Double.plus(c: Complex): Complex = add(this.toComplex(), c)
 
-    operator fun Double.minus(c: Complex) = add(this.toComplex(), -c)
+    /**
+     * Subtracts complex number from real one.
+     *
+     * @receiver the minuend.
+     * @param c the subtrahend.
+     * @return the difference.
+     */
+    operator fun Double.minus(c: Complex): Complex = add(this.toComplex(), -c)
 
-    operator fun Complex.plus(d: Double) = d + this
+    /**
+     * Adds real number to complex one.
+     *
+     * @receiver the addend.
+     * @param d the augend.
+     * @return the sum.
+     */
+    operator fun Complex.plus(d: Double): Complex = d + this
 
-    operator fun Complex.minus(d: Double) = add(this, -d.toComplex())
+    /**
+     * Subtracts real number from complex one.
+     *
+     * @receiver the minuend.
+     * @param d the subtrahend.
+     * @return the difference.
+     */
+    operator fun Complex.minus(d: Double): Complex = add(this, -d.toComplex())
 
-    operator fun Double.times(c: Complex) = Complex(c.re * this, c.im * this)
+    /**
+     * Multiplies real number by complex one.
+     *
+     * @receiver the multiplier.
+     * @param c the multiplicand.
+     * @receiver the product.
+     */
+    operator fun Double.times(c: Complex): Complex = Complex(c.re * this, c.im * this)
 
-    override fun symbol(value: String): Complex = if (value == "i") {
-        i
-    } else {
-        super.symbol(value)
-    }
+    override fun norm(arg: Complex): Complex = sqrt(arg.conjugate * arg)
+
+    override fun symbol(value: String): Complex = if (value == "i") i else super.symbol(value)
 }
 
 /**
- * Complex number class
+ * Represents complex number.
+ *
+ * @property re The real part.
+ * @property im The imaginary part.
  */
 data class Complex(val re: Double, val im: Double) : FieldElement<Complex, Complex, ComplexField>, Comparable<Complex> {
     constructor(re: Number, im: Number) : this(re.toDouble(), im.toDouble())
 
+    override val context: ComplexField get() = ComplexField
+
     override fun unwrap(): Complex = this
 
     override fun Complex.wrap(): Complex = this
 
-    override val context: ComplexField get() = ComplexField
-
     override fun compareTo(other: Complex): Int = r.compareTo(other.r)
 
     companion object : MemorySpec<Complex> {
@@ -90,26 +191,19 @@ data class Complex(val re: Double, val im: Double) : FieldElement<Complex, Compl
 }
 
 /**
- * A complex conjugate
+ * Creates a complex number with real part equal to this real.
+ *
+ * @receiver the real part.
+ * @return the new complex number.
  */
-val Complex.conjugate: Complex get() = Complex(re, -im)
-
-/**
- * Absolute value of complex number
- */
-val Complex.r: Double get() = sqrt(re * re + im * im)
-
-/**
- * An angle between vector represented by complex number and X axis
- */
-val Complex.theta: Double get() = atan(im / re)
-
-fun Double.toComplex() = Complex(this, 0.0)
+fun Number.toComplex(): Complex = Complex(this, 0.0)
 
 inline fun Buffer.Companion.complex(size: Int, crossinline init: (Int) -> Complex): Buffer<Complex> {
+    contract { callsInPlace(init) }
     return MemoryBuffer.create(Complex, size, init)
 }
 
 inline fun MutableBuffer.Companion.complex(size: Int, crossinline init: (Int) -> Complex): Buffer<Complex> {
+    contract { callsInPlace(init) }
     return MemoryBuffer.create(Complex, size, init)
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/operations/NumberAlgebra.kt

@@ -1,25 +1,35 @@
 package scientifik.kmath.operations
 
+import scientifik.kmath.operations.RealField.pow
 import kotlin.math.abs
 import kotlin.math.pow as kpow
 
 /**
- * Advanced Number-like field that implements basic operations
+ * Advanced Number-like semifield that implements basic operations.
  */
 interface ExtendedFieldOperations<T> :
-    InverseTrigonometricOperations<T>,
+    FieldOperations<T>,
+    TrigonometricOperations<T>,
+    HyperbolicOperations<T>,
     PowerOperations<T>,
     ExponentialOperations<T> {
 
     override fun tan(arg: T): T = sin(arg) / cos(arg)
+    override fun tanh(arg: T): T = sinh(arg) / cosh(arg)
 
     override fun unaryOperation(operation: String, arg: T): T = when (operation) {
         TrigonometricOperations.COS_OPERATION -> cos(arg)
         TrigonometricOperations.SIN_OPERATION -> sin(arg)
         TrigonometricOperations.TAN_OPERATION -> tan(arg)
-        InverseTrigonometricOperations.ACOS_OPERATION -> acos(arg)
-        InverseTrigonometricOperations.ASIN_OPERATION -> asin(arg)
-        InverseTrigonometricOperations.ATAN_OPERATION -> atan(arg)
+        TrigonometricOperations.ACOS_OPERATION -> acos(arg)
+        TrigonometricOperations.ASIN_OPERATION -> asin(arg)
+        TrigonometricOperations.ATAN_OPERATION -> atan(arg)
+        HyperbolicOperations.COSH_OPERATION -> cosh(arg)
+        HyperbolicOperations.SINH_OPERATION -> sinh(arg)
+        HyperbolicOperations.TANH_OPERATION -> tanh(arg)
+        HyperbolicOperations.ACOSH_OPERATION -> acosh(arg)
+        HyperbolicOperations.ASINH_OPERATION -> asinh(arg)
+        HyperbolicOperations.ATANH_OPERATION -> atanh(arg)
         PowerOperations.SQRT_OPERATION -> sqrt(arg)
         ExponentialOperations.EXP_OPERATION -> exp(arg)
         ExponentialOperations.LN_OPERATION -> ln(arg)
@@ -27,7 +37,18 @@ interface ExtendedFieldOperations<T> :
     }
 }
 
+
+/**
+ * Advanced Number-like field that implements basic operations.
+ */
 interface ExtendedField<T> : ExtendedFieldOperations<T>, Field<T> {
+    override fun sinh(arg: T): T = (exp(arg) - exp(-arg)) / 2
+    override fun cosh(arg: T): T = (exp(arg) + exp(-arg)) / 2
+    override fun tanh(arg: T): T = (exp(arg) - exp(-arg)) / (exp(-arg) + exp(arg))
+    override fun asinh(arg: T): T = ln(sqrt(arg * arg + one) + arg)
+    override fun acosh(arg: T): T = ln(arg + sqrt((arg - one) * (arg + one)))
+    override fun atanh(arg: T): T = (ln(arg + one) - ln(one - arg)) / 2
+
     override fun rightSideNumberOperation(operation: String, left: T, right: Number): T = when (operation) {
         PowerOperations.POW_OPERATION -> power(left, right)
         else -> super.rightSideNumberOperation(operation, left, right)
@@ -37,175 +58,213 @@ interface ExtendedField<T> : ExtendedFieldOperations<T>, Field<T> {
 /**
  * Real field element wrapping double.
  *
+ * @property value the [Double] value wrapped by this [Real].
+ *
  * TODO inline does not work due to compiler bug. Waiting for fix for KT-27586
  */
 inline class Real(val value: Double) : FieldElement<Double, Real, RealField> {
+    override val context: RealField
+        get() = RealField
+
     override fun unwrap(): Double = value
 
     override fun Double.wrap(): Real = Real(value)
 
-    override val context get() = RealField
-
     companion object
 }
 
 /**
- * A field for double without boxing. Does not produce appropriate field element
+ * A field for [Double] without boxing. Does not produce appropriate field element.
  */
 @Suppress("EXTENSION_SHADOWED_BY_MEMBER", "OVERRIDE_BY_INLINE", "NOTHING_TO_INLINE")
 object RealField : ExtendedField<Double>, Norm<Double, Double> {
-    override val zero: Double = 0.0
-    override inline fun add(a: Double, b: Double) = a + b
-    override inline fun multiply(a: Double, b: Double) = a * b
-    override inline fun multiply(a: Double, k: Number) = a * k.toDouble()
+    override val zero: Double
+        get() = 0.0
 
-    override val one: Double = 1.0
-    override inline fun divide(a: Double, b: Double) = a / b
+    override val one: Double
+        get() = 1.0
 
-    override inline fun sin(arg: Double) = kotlin.math.sin(arg)
-    override inline fun cos(arg: Double) = kotlin.math.cos(arg)
+    override fun binaryOperation(operation: String, left: Double, right: Double): Double = when (operation) {
+        PowerOperations.POW_OPERATION -> left pow right
+        else -> super.binaryOperation(operation, left, right)
+    }
+
+    override inline fun add(a: Double, b: Double): Double = a + b
+    override inline fun multiply(a: Double, k: Number): Double = a * k.toDouble()
+
+    override inline fun multiply(a: Double, b: Double): Double = a * b
+
+    override inline fun divide(a: Double, b: Double): Double = a / b
+
+    override inline fun sin(arg: Double): Double = kotlin.math.sin(arg)
+    override inline fun cos(arg: Double): Double = kotlin.math.cos(arg)
     override inline fun tan(arg: Double): Double = kotlin.math.tan(arg)
     override inline fun acos(arg: Double): Double = kotlin.math.acos(arg)
     override inline fun asin(arg: Double): Double = kotlin.math.asin(arg)
     override inline fun atan(arg: Double): Double = kotlin.math.atan(arg)
 
-    override inline fun power(arg: Double, pow: Number) = arg.kpow(pow.toDouble())
+    override inline fun sinh(arg: Double): Double = kotlin.math.sinh(arg)
+    override inline fun cosh(arg: Double): Double = kotlin.math.cosh(arg)
+    override inline fun tanh(arg: Double): Double = kotlin.math.tanh(arg)
+    override inline fun asinh(arg: Double): Double = kotlin.math.asinh(arg)
+    override inline fun acosh(arg: Double): Double = kotlin.math.acosh(arg)
+    override inline fun atanh(arg: Double): Double = kotlin.math.atanh(arg)
 
-    override inline fun exp(arg: Double) = kotlin.math.exp(arg)
-    override inline fun ln(arg: Double) = kotlin.math.ln(arg)
+    override inline fun power(arg: Double, pow: Number): Double = arg.kpow(pow.toDouble())
+    override inline fun exp(arg: Double): Double = kotlin.math.exp(arg)
+    override inline fun ln(arg: Double): Double = kotlin.math.ln(arg)
 
-    override inline fun norm(arg: Double) = abs(arg)
+    override inline fun norm(arg: Double): Double = abs(arg)
 
-    override inline fun Double.unaryMinus() = -this
-
-    override inline fun Double.plus(b: Double) = this + b
-
-    override inline fun Double.minus(b: Double) = this - b
-
-    override inline fun Double.times(b: Double) = this * b
-
-    override inline fun Double.div(b: Double) = this / b
-}
-
-@Suppress("EXTENSION_SHADOWED_BY_MEMBER", "OVERRIDE_BY_INLINE", "NOTHING_TO_INLINE")
-object FloatField : ExtendedField<Float>, Norm<Float, Float> {
-    override val zero: Float = 0f
-    override inline fun add(a: Float, b: Float) = a + b
-    override inline fun multiply(a: Float, b: Float) = a * b
-    override inline fun multiply(a: Float, k: Number) = a * k.toFloat()
-
-    override val one: Float = 1f
-    override inline fun divide(a: Float, b: Float) = a / b
-
-    override inline fun sin(arg: Float) = kotlin.math.sin(arg)
-    override inline fun cos(arg: Float) = kotlin.math.cos(arg)
-    override inline fun tan(arg: Float) = kotlin.math.tan(arg)
-    override inline fun acos(arg: Float) = kotlin.math.acos(arg)
-    override inline fun asin(arg: Float) = kotlin.math.asin(arg)
-    override inline fun atan(arg: Float) = kotlin.math.atan(arg)
-
-    override inline fun power(arg: Float, pow: Number) = arg.pow(pow.toFloat())
-
-    override inline fun exp(arg: Float) = kotlin.math.exp(arg)
-    override inline fun ln(arg: Float) = kotlin.math.ln(arg)
-
-    override inline fun norm(arg: Float) = abs(arg)
-
-    override inline fun Float.unaryMinus() = -this
-
-    override inline fun Float.plus(b: Float) = this + b
-
-    override inline fun Float.minus(b: Float) = this - b
-
-    override inline fun Float.times(b: Float) = this * b
-
-    override inline fun Float.div(b: Float) = this / b
+    override inline fun Double.unaryMinus(): Double = -this
+    override inline fun Double.plus(b: Double): Double = this + b
+    override inline fun Double.minus(b: Double): Double = this - b
+    override inline fun Double.times(b: Double): Double = this * b
+    override inline fun Double.div(b: Double): Double = this / b
 }
 
 /**
- * A field for [Int] without boxing. Does not produce corresponding field element
+ * A field for [Float] without boxing. Does not produce appropriate field element.
+ */
+@Suppress("EXTENSION_SHADOWED_BY_MEMBER", "OVERRIDE_BY_INLINE", "NOTHING_TO_INLINE")
+object FloatField : ExtendedField<Float>, Norm<Float, Float> {
+    override val zero: Float
+        get() = 0.0f
+
+    override val one: Float
+        get() = 1.0f
+
+    override fun binaryOperation(operation: String, left: Float, right: Float): Float = when (operation) {
+        PowerOperations.POW_OPERATION -> left pow right
+        else -> super.binaryOperation(operation, left, right)
+    }
+
+    override inline fun add(a: Float, b: Float): Float = a + b
+    override inline fun multiply(a: Float, k: Number): Float = a * k.toFloat()
+
+    override inline fun multiply(a: Float, b: Float): Float = a * b
+
+    override inline fun divide(a: Float, b: Float): Float = a / b
+
+    override inline fun sin(arg: Float): Float = kotlin.math.sin(arg)
+    override inline fun cos(arg: Float): Float = kotlin.math.cos(arg)
+    override inline fun tan(arg: Float): Float = kotlin.math.tan(arg)
+    override inline fun acos(arg: Float): Float = kotlin.math.acos(arg)
+    override inline fun asin(arg: Float): Float = kotlin.math.asin(arg)
+    override inline fun atan(arg: Float): Float = kotlin.math.atan(arg)
+
+    override inline fun sinh(arg: Float): Float = kotlin.math.sinh(arg)
+    override inline fun cosh(arg: Float): Float = kotlin.math.cosh(arg)
+    override inline fun tanh(arg: Float): Float = kotlin.math.tanh(arg)
+    override inline fun asinh(arg: Float): Float = kotlin.math.asinh(arg)
+    override inline fun acosh(arg: Float): Float = kotlin.math.acosh(arg)
+    override inline fun atanh(arg: Float): Float = kotlin.math.atanh(arg)
+
+    override inline fun power(arg: Float, pow: Number): Float = arg.kpow(pow.toFloat())
+    override inline fun exp(arg: Float): Float = kotlin.math.exp(arg)
+    override inline fun ln(arg: Float): Float = kotlin.math.ln(arg)
+
+    override inline fun norm(arg: Float): Float = abs(arg)
+
+    override inline fun Float.unaryMinus(): Float = -this
+    override inline fun Float.plus(b: Float): Float = this + b
+    override inline fun Float.minus(b: Float): Float = this - b
+    override inline fun Float.times(b: Float): Float = this * b
+    override inline fun Float.div(b: Float): Float = this / b
+}
+
+/**
+ * A field for [Int] without boxing. Does not produce corresponding ring element.
  */
 @Suppress("EXTENSION_SHADOWED_BY_MEMBER", "OVERRIDE_BY_INLINE", "NOTHING_TO_INLINE")
 object IntRing : Ring<Int>, Norm<Int, Int> {
-    override val zero: Int = 0
-    override inline fun add(a: Int, b: Int) = a + b
-    override inline fun multiply(a: Int, b: Int) = a * b
-    override inline fun multiply(a: Int, k: Number) = k.toInt() * a
-    override val one: Int = 1
+    override val zero: Int
+        get() = 0
 
-    override inline fun norm(arg: Int) = abs(arg)
+    override val one: Int
+        get() = 1
 
-    override inline fun Int.unaryMinus() = -this
+    override inline fun add(a: Int, b: Int): Int = a + b
+    override inline fun multiply(a: Int, k: Number): Int = k.toInt() * a
 
+    override inline fun multiply(a: Int, b: Int): Int = a * b
+
+    override inline fun norm(arg: Int): Int = abs(arg)
+
+    override inline fun Int.unaryMinus(): Int = -this
     override inline fun Int.plus(b: Int): Int = this + b
-
     override inline fun Int.minus(b: Int): Int = this - b
-
     override inline fun Int.times(b: Int): Int = this * b
 }
 
 /**
- * A field for [Short] without boxing. Does not produce appropriate field element
+ * A field for [Short] without boxing. Does not produce appropriate ring element.
  */
 @Suppress("EXTENSION_SHADOWED_BY_MEMBER", "OVERRIDE_BY_INLINE", "NOTHING_TO_INLINE")
 object ShortRing : Ring<Short>, Norm<Short, Short> {
-    override val zero: Short = 0
-    override inline fun add(a: Short, b: Short) = (a + b).toShort()
-    override inline fun multiply(a: Short, b: Short) = (a * b).toShort()
-    override inline fun multiply(a: Short, k: Number) = (a * k.toShort()).toShort()
-    override val one: Short = 1
+    override val zero: Short
+        get() = 0
+
+    override val one: Short
+        get() = 1
+
+    override inline fun add(a: Short, b: Short): Short = (a + b).toShort()
+    override inline fun multiply(a: Short, k: Number): Short = (a * k.toShort()).toShort()
+
+    override inline fun multiply(a: Short, b: Short): Short = (a * b).toShort()
 
     override fun norm(arg: Short): Short = if (arg > 0) arg else (-arg).toShort()
 
-    override inline fun Short.unaryMinus() = (-this).toShort()
-
-    override inline fun Short.plus(b: Short) = (this + b).toShort()
-
-    override inline fun Short.minus(b: Short) = (this - b).toShort()
-
-    override inline fun Short.times(b: Short) = (this * b).toShort()
+    override inline fun Short.unaryMinus(): Short = (-this).toShort()
+    override inline fun Short.plus(b: Short): Short = (this + b).toShort()
+    override inline fun Short.minus(b: Short): Short = (this - b).toShort()
+    override inline fun Short.times(b: Short): Short = (this * b).toShort()
 }
 
 /**
- * A field for [Byte] values
+ * A field for [Byte] without boxing. Does not produce appropriate ring element.
  */
 @Suppress("EXTENSION_SHADOWED_BY_MEMBER", "OVERRIDE_BY_INLINE", "NOTHING_TO_INLINE")
 object ByteRing : Ring<Byte>, Norm<Byte, Byte> {
-    override val zero: Byte = 0
-    override inline fun add(a: Byte, b: Byte) = (a + b).toByte()
-    override inline fun multiply(a: Byte, b: Byte) = (a * b).toByte()
-    override inline fun multiply(a: Byte, k: Number) = (a * k.toByte()).toByte()
-    override val one: Byte = 1
+    override val zero: Byte
+        get() = 0
+
+    override val one: Byte
+        get() = 1
+
+    override inline fun add(a: Byte, b: Byte): Byte = (a + b).toByte()
+    override inline fun multiply(a: Byte, k: Number): Byte = (a * k.toByte()).toByte()
+
+    override inline fun multiply(a: Byte, b: Byte): Byte = (a * b).toByte()
 
     override fun norm(arg: Byte): Byte = if (arg > 0) arg else (-arg).toByte()
 
-    override inline fun Byte.unaryMinus() = (-this).toByte()
-
-    override inline fun Byte.plus(b: Byte) = (this + b).toByte()
-
-    override inline fun Byte.minus(b: Byte) = (this - b).toByte()
-
-    override inline fun Byte.times(b: Byte) = (this * b).toByte()
+    override inline fun Byte.unaryMinus(): Byte = (-this).toByte()
+    override inline fun Byte.plus(b: Byte): Byte = (this + b).toByte()
+    override inline fun Byte.minus(b: Byte): Byte = (this - b).toByte()
+    override inline fun Byte.times(b: Byte): Byte = (this * b).toByte()
 }
 
 /**
- * A field for [Long] values
+ * A field for [Double] without boxing. Does not produce appropriate ring element.
  */
 @Suppress("EXTENSION_SHADOWED_BY_MEMBER", "OVERRIDE_BY_INLINE", "NOTHING_TO_INLINE")
 object LongRing : Ring<Long>, Norm<Long, Long> {
-    override val zero: Long = 0
-    override inline fun add(a: Long, b: Long) = (a + b)
-    override inline fun multiply(a: Long, b: Long) = (a * b)
-    override inline fun multiply(a: Long, k: Number) = a * k.toLong()
-    override val one: Long = 1
+    override val zero: Long
+        get() = 0
+
+    override val one: Long
+        get() = 1
+
+    override inline fun add(a: Long, b: Long): Long = a + b
+    override inline fun multiply(a: Long, k: Number): Long = a * k.toLong()
+
+    override inline fun multiply(a: Long, b: Long): Long = a * b
 
     override fun norm(arg: Long): Long = abs(arg)
 
-    override inline fun Long.unaryMinus() = (-this)
-
-    override inline fun Long.plus(b: Long) = (this + b)
-
-    override inline fun Long.minus(b: Long) = (this - b)
-
-    override inline fun Long.times(b: Long) = (this * b)
+    override inline fun Long.unaryMinus(): Long = (-this)
+    override inline fun Long.plus(b: Long): Long = (this + b)
+    override inline fun Long.minus(b: Long): Long = (this - b)
+    override inline fun Long.times(b: Long): Long = (this * b)
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/operations/OptionalOperations.kt

@@ -1,84 +1,309 @@
 package scientifik.kmath.operations
 
-
-/* Trigonometric operations */
-
 /**
- * A container for trigonometric operations for specific type. Trigonometric operations are limited to fields.
- *
- * The operations are not exposed to class directly to avoid method bloat but instead are declared in the field.
- * It also allows to override behavior for optional operations
+ * A container for trigonometric operations for specific type.
  *
+ * @param T the type of element of this structure.
+ */
+interface TrigonometricOperations<T> : Algebra<T> {
+    /**
+     * Computes the sine of [arg].
      */
-interface TrigonometricOperations<T> : FieldOperations<T> {
     fun sin(arg: T): T
+
+    /**
+     * Computes the cosine of [arg].
+     */
     fun cos(arg: T): T
+
+    /**
+     * Computes the tangent of [arg].
+     */
     fun tan(arg: T): T
 
-    companion object {
-        const val SIN_OPERATION = "sin"
-        const val COS_OPERATION = "cos"
-        const val TAN_OPERATION = "tan"
-    }
-}
-
-interface InverseTrigonometricOperations<T> : TrigonometricOperations<T> {
+    /**
+     * Computes the inverse sine of [arg].
+     */
     fun asin(arg: T): T
+
+    /**
+     * Computes the inverse cosine of [arg].
+     */
     fun acos(arg: T): T
+
+    /**
+     * Computes the inverse tangent of [arg].
+     */
     fun atan(arg: T): T
 
     companion object {
-        const val ASIN_OPERATION = "asin"
-        const val ACOS_OPERATION = "acos"
-        const val ATAN_OPERATION = "atan"
+        /**
+         * The identifier of sine.
+         */
+        const val SIN_OPERATION: String = "sin"
+
+        /**
+         * The identifier of cosine.
+         */
+        const val COS_OPERATION: String = "cos"
+
+        /**
+         * The identifier of tangent.
+         */
+        const val TAN_OPERATION: String = "tan"
+
+        /**
+         * The identifier of inverse sine.
+         */
+        const val ASIN_OPERATION: String = "asin"
+
+        /**
+         * The identifier of inverse cosine.
+         */
+        const val ACOS_OPERATION: String = "acos"
+
+        /**
+         * The identifier of inverse tangent.
+         */
+        const val ATAN_OPERATION: String = "atan"
     }
 }
 
-fun <T : MathElement<out TrigonometricOperations<T>>> sin(arg: T): T = arg.context.sin(arg)
-fun <T : MathElement<out TrigonometricOperations<T>>> cos(arg: T): T = arg.context.cos(arg)
-fun <T : MathElement<out TrigonometricOperations<T>>> tan(arg: T): T = arg.context.tan(arg)
-fun <T : MathElement<out InverseTrigonometricOperations<T>>> asin(arg: T): T = arg.context.asin(arg)
-fun <T : MathElement<out InverseTrigonometricOperations<T>>> acos(arg: T): T = arg.context.acos(arg)
-fun <T : MathElement<out InverseTrigonometricOperations<T>>> atan(arg: T): T = arg.context.atan(arg)
-
-/* Power and roots */
-
 /**
- * A context extension to include power operations like square roots, etc
+ * Computes the sine of [arg].
  */
-interface PowerOperations<T> : Algebra<T> {
-    fun power(arg: T, pow: Number): T
-    fun sqrt(arg: T) = power(arg, 0.5)
+fun <T : MathElement<out TrigonometricOperations<T>>> sin(arg: T): T = arg.context.sin(arg)
 
-    infix fun T.pow(pow: Number) = power(this, pow)
+/**
+ * Computes the cosine of [arg].
+ */
+fun <T : MathElement<out TrigonometricOperations<T>>> cos(arg: T): T = arg.context.cos(arg)
+
+/**
+ * Computes the tangent of [arg].
+ */
+fun <T : MathElement<out TrigonometricOperations<T>>> tan(arg: T): T = arg.context.tan(arg)
+
+/**
+ * Computes the inverse sine of [arg].
+ */
+fun <T : MathElement<out TrigonometricOperations<T>>> asin(arg: T): T = arg.context.asin(arg)
+
+/**
+ * Computes the inverse cosine of [arg].
+ */
+fun <T : MathElement<out TrigonometricOperations<T>>> acos(arg: T): T = arg.context.acos(arg)
+
+/**
+ * Computes the inverse tangent of [arg].
+ */
+fun <T : MathElement<out TrigonometricOperations<T>>> atan(arg: T): T = arg.context.atan(arg)
+
+/**
+ * A container for hyperbolic trigonometric operations for specific type.
+ *
+ * @param T the type of element of this structure.
+ */
+interface HyperbolicOperations<T> : Algebra<T> {
+    /**
+     * Computes the hyperbolic sine of [arg].
+     */
+    fun sinh(arg: T): T
+
+    /**
+     * Computes the hyperbolic cosine of [arg].
+     */
+    fun cosh(arg: T): T
+
+    /**
+     * Computes the hyperbolic tangent of [arg].
+     */
+    fun tanh(arg: T): T
+
+    /**
+     * Computes the inverse hyperbolic sine of [arg].
+     */
+    fun asinh(arg: T): T
+
+    /**
+     * Computes the inverse hyperbolic cosine of [arg].
+     */
+    fun acosh(arg: T): T
+
+    /**
+     * Computes the inverse hyperbolic tangent of [arg].
+     */
+    fun atanh(arg: T): T
 
     companion object {
-        const val POW_OPERATION = "pow"
-        const val SQRT_OPERATION = "sqrt"
+        /**
+         * The identifier of hyperbolic sine.
+         */
+        const val SINH_OPERATION: String = "sinh"
+
+        /**
+         * The identifier of hyperbolic cosine.
+         */
+        const val COSH_OPERATION: String = "cosh"
+
+        /**
+         * The identifier of hyperbolic tangent.
+         */
+        const val TANH_OPERATION: String = "tanh"
+
+        /**
+         * The identifier of inverse hyperbolic sine.
+         */
+        const val ASINH_OPERATION: String = "asinh"
+
+        /**
+         * The identifier of inverse hyperbolic cosine.
+         */
+        const val ACOSH_OPERATION: String = "acosh"
+
+        /**
+         * The identifier of inverse hyperbolic tangent.
+         */
+        const val ATANH_OPERATION: String = "atanh"
     }
 }
 
+/**
+ * Computes the hyperbolic sine of [arg].
+ */
+fun <T : MathElement<out HyperbolicOperations<T>>> sinh(arg: T): T = arg.context.sinh(arg)
+
+/**
+ * Computes the hyperbolic cosine of [arg].
+ */
+fun <T : MathElement<out HyperbolicOperations<T>>> cosh(arg: T): T = arg.context.cosh(arg)
+
+/**
+ * Computes the hyperbolic tangent of [arg].
+ */
+fun <T : MathElement<out HyperbolicOperations<T>>> tanh(arg: T): T = arg.context.tanh(arg)
+
+/**
+ * Computes the inverse hyperbolic sine of [arg].
+ */
+fun <T : MathElement<out HyperbolicOperations<T>>> asinh(arg: T): T = arg.context.asinh(arg)
+
+/**
+ * Computes the inverse hyperbolic cosine of [arg].
+ */
+fun <T : MathElement<out HyperbolicOperations<T>>> acosh(arg: T): T = arg.context.acosh(arg)
+
+/**
+ * Computes the inverse hyperbolic tangent of [arg].
+ */
+fun <T : MathElement<out HyperbolicOperations<T>>> atanh(arg: T): T = arg.context.atanh(arg)
+
+/**
+ * A context extension to include power operations based on exponentiation.
+ *
+ * @param T the type of element of this structure.
+ */
+interface PowerOperations<T> : Algebra<T> {
+    /**
+     * Raises [arg] to the power [pow].
+     */
+    fun power(arg: T, pow: Number): T
+
+    /**
+     * Computes the square root of the value [arg].
+     */
+    fun sqrt(arg: T): T = power(arg, 0.5)
+
+    /**
+     * Raises this value to the power [pow].
+     */
+    infix fun T.pow(pow: Number): T = power(this, pow)
+
+    companion object {
+        /**
+         * The identifier of exponentiation.
+         */
+        const val POW_OPERATION: String = "pow"
+
+        /**
+         * The identifier of square root.
+         */
+        const val SQRT_OPERATION: String = "sqrt"
+    }
+}
+
+/**
+ * Raises this element to the power [pow].
+ *
+ * @receiver the base.
+ * @param power the exponent.
+ * @return the base raised to the power.
+ */
 infix fun <T : MathElement<out PowerOperations<T>>> T.pow(power: Double): T = context.power(this, power)
+
+/**
+ * Computes the square root of the value [arg].
+ */
 fun <T : MathElement<out PowerOperations<T>>> sqrt(arg: T): T = arg pow 0.5
+
+/**
+ * Computes the square of the value [arg].
+ */
 fun <T : MathElement<out PowerOperations<T>>> sqr(arg: T): T = arg pow 2.0
 
-/* Exponential */
-
+/**
+ * A container for operations related to `exp` and `ln` functions.
+ *
+ * @param T the type of element of this structure.
+ */
 interface ExponentialOperations<T> : Algebra<T> {
+    /**
+     * Computes Euler's number `e` raised to the power of the value [arg].
+     */
     fun exp(arg: T): T
+
+    /**
+     * Computes the natural logarithm (base `e`) of the value [arg].
+     */
     fun ln(arg: T): T
 
     companion object {
-        const val EXP_OPERATION = "exp"
-        const val LN_OPERATION = "ln"
+        /**
+         * The identifier of exponential function.
+         */
+        const val EXP_OPERATION: String = "exp"
+
+        /**
+         * The identifier of natural logarithm.
+         */
+        const val LN_OPERATION: String = "ln"
     }
 }
 
+/**
+ * The identifier of exponential function.
+ */
 fun <T : MathElement<out ExponentialOperations<T>>> exp(arg: T): T = arg.context.exp(arg)
+
+/**
+ * The identifier of natural logarithm.
+ */
 fun <T : MathElement<out ExponentialOperations<T>>> ln(arg: T): T = arg.context.ln(arg)
 
+/**
+ * A container for norm functional on element.
+ *
+ * @param T the type of element having norm defined.
+ * @param R the type of norm.
+ */
 interface Norm<in T : Any, out R> {
+    /**
+     * Computes the norm of [arg] (i.e. absolute value or vector length).
+     */
     fun norm(arg: T): R
 }
 
+/**
+ * Computes the norm of [arg] (i.e. absolute value or vector length).
+ */
 fun <T : MathElement<out Norm<T, R>>, R> norm(arg: T): R = arg.context.norm(arg)

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/BoxingNDField.kt

@@ -3,32 +3,30 @@ package scientifik.kmath.structures
 import scientifik.kmath.operations.Field
 import scientifik.kmath.operations.FieldElement
 
-
 class BoxingNDField<T, F : Field<T>>(
     override val shape: IntArray,
     override val elementContext: F,
     val bufferFactory: BufferFactory<T>
 ) : BufferedNDField<T, F> {
-
+    override val zero: BufferedNDFieldElement<T, F> by lazy { produce { zero } }
+    override val one: BufferedNDFieldElement<T, F> by lazy { produce { one } }
     override val strides: Strides = DefaultStrides(shape)
 
     fun buildBuffer(size: Int, initializer: (Int) -> T): Buffer<T> =
         bufferFactory(size, initializer)
 
     override fun check(vararg elements: NDBuffer<T>) {
-        if (!elements.all { it.strides == this.strides }) error("Element strides are not the same as context strides")
+        check(elements.all { it.strides == strides }) { "Element strides are not the same as context strides" }
     }
 
-    override val zero by lazy { produce { zero } }
-    override val one by lazy { produce { one } }
-
-    override fun produce(initializer: F.(IntArray) -> T) =
+    override fun produce(initializer: F.(IntArray) -> T): BufferedNDFieldElement<T, F> =
         BufferedNDFieldElement(
             this,
             buildBuffer(strides.linearSize) { offset -> elementContext.initializer(strides.index(offset)) })
 
     override fun map(arg: NDBuffer<T>, transform: F.(T) -> T): BufferedNDFieldElement<T, F> {
         check(arg)
+
         return BufferedNDFieldElement(
             this,
             buildBuffer(arg.strides.linearSize) { offset -> elementContext.transform(arg.buffer[offset]) })

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/BoxingNDRing.kt

@@ -8,20 +8,17 @@ class BoxingNDRing<T, R : Ring<T>>(
     override val elementContext: R,
     val bufferFactory: BufferFactory<T>
 ) : BufferedNDRing<T, R> {
-
     override val strides: Strides = DefaultStrides(shape)
+    override val zero: BufferedNDRingElement<T, R> by lazy { produce { zero } }
+    override val one: BufferedNDRingElement<T, R> by lazy { produce { one } }
 
-    fun buildBuffer(size: Int, initializer: (Int) -> T): Buffer<T> =
-        bufferFactory(size, initializer)
+    fun buildBuffer(size: Int, initializer: (Int) -> T): Buffer<T> = bufferFactory(size, initializer)
 
     override fun check(vararg elements: NDBuffer<T>) {
-        if (!elements.all { it.strides == this.strides }) error("Element strides are not the same as context strides")
+        require(elements.all { it.strides == strides }) { "Element strides are not the same as context strides" }
     }
 
-    override val zero by lazy { produce { zero } }
-    override val one by lazy { produce { one } }
-
-    override fun produce(initializer: R.(IntArray) -> T) =
+    override fun produce(initializer: R.(IntArray) -> T): BufferedNDRingElement<T, R> =
         BufferedNDRingElement(
             this,
             buildBuffer(strides.linearSize) { offset -> elementContext.initializer(strides.index(offset)) })

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/BufferAccessor2D.kt

@@ -6,17 +6,16 @@ import kotlin.reflect.KClass
  * A context that allows to operate on a [MutableBuffer] as on 2d array
  */
 class BufferAccessor2D<T : Any>(val type: KClass<T>, val rowNum: Int, val colNum: Int) {
-
-    operator fun Buffer<T>.get(i: Int, j: Int) = get(i + colNum * j)
+    operator fun Buffer<T>.get(i: Int, j: Int): T = get(i + colNum * j)
 
     operator fun MutableBuffer<T>.set(i: Int, j: Int, value: T) {
         set(i + colNum * j, value)
     }
 
-    inline fun create(init: (i: Int, j: Int) -> T) =
+    inline fun create(init: (i: Int, j: Int) -> T): MutableBuffer<T> =
         MutableBuffer.auto(type, rowNum * colNum) { offset -> init(offset / colNum, offset % colNum) }
 
-    fun create(mat: Structure2D<T>) = create { i, j -> mat[i, j] }
+    fun create(mat: Structure2D<T>): MutableBuffer<T> = create { i, j -> mat[i, j] }
 
     //TODO optimize wrapper
     fun MutableBuffer<T>.collect(): Structure2D<T> =
@@ -26,20 +25,19 @@ class BufferAccessor2D<T : Any>(val type: KClass<T>, val rowNum: Int, val colNum
     inner class Row(val buffer: MutableBuffer<T>, val rowIndex: Int) : MutableBuffer<T> {
         override val size: Int get() = colNum
 
-        override fun get(index: Int): T = buffer[rowIndex, index]
+        override operator fun get(index: Int): T = buffer[rowIndex, index]
 
-        override fun set(index: Int, value: T) {
+        override operator fun set(index: Int, value: T) {
             buffer[rowIndex, index] = value
         }
 
         override fun copy(): MutableBuffer<T> = MutableBuffer.auto(type, colNum) { get(it) }
-
-        override fun iterator(): Iterator<T> = (0 until colNum).map(::get).iterator()
+        override operator fun iterator(): Iterator<T> = (0 until colNum).map(::get).iterator()
 
     }
 
     /**
      * Get row
      */
-    fun MutableBuffer<T>.row(i: Int) = Row(this, i)
+    fun MutableBuffer<T>.row(i: Int): Row = Row(this, i)
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/BufferedNDAlgebra.kt

@@ -2,16 +2,16 @@ package scientifik.kmath.structures
 
 import scientifik.kmath.operations.*
 
-interface BufferedNDAlgebra<T, C>: NDAlgebra<T, C, NDBuffer<T>>{
+interface BufferedNDAlgebra<T, C> : NDAlgebra<T, C, NDBuffer<T>> {
     val strides: Strides
 
-    override fun check(vararg elements: NDBuffer<T>) {
-        if (!elements.all { it.strides == this.strides }) error("Strides mismatch")
-    }
+    override fun check(vararg elements: NDBuffer<T>): Unit =
+        require(elements.all { it.strides == strides }) { ("Strides mismatch") }
 
     /**
      * Convert any [NDStructure] to buffered structure using strides from this context.
-     * If the structure is already [NDBuffer], conversion is free. If not, it could be expensive because iteration over indexes
+     * If the structure is already [NDBuffer], conversion is free. If not, it could be expensive because iteration over
+     * indices.
      *
      * If the argument is [NDBuffer] with different strides structure, the new element will be produced.
      */
@@ -30,7 +30,7 @@ interface BufferedNDAlgebra<T, C>: NDAlgebra<T, C, NDBuffer<T>>{
 }
 
 
-interface BufferedNDSpace<T, S : Space<T>> : NDSpace<T, S, NDBuffer<T>>, BufferedNDAlgebra<T,S>  {
+interface BufferedNDSpace<T, S : Space<T>> : NDSpace<T, S, NDBuffer<T>>, BufferedNDAlgebra<T, S> {
     override fun NDBuffer<T>.toElement(): SpaceElement<NDBuffer<T>, *, out BufferedNDSpace<T, S>>
 }
 

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/BufferedNDElement.kt

@@ -8,7 +8,7 @@ import scientifik.kmath.operations.*
 abstract class BufferedNDElement<T, C> : NDBuffer<T>(), NDElement<T, C, NDBuffer<T>> {
     abstract override val context: BufferedNDAlgebra<T, C>
 
-    override val strides get() = context.strides
+    override val strides: Strides get() = context.strides
 
     override val shape: IntArray get() = context.shape
 }
@@ -30,7 +30,6 @@ class BufferedNDRingElement<T, R : Ring<T>>(
     override val context: BufferedNDRing<T, R>,
     override val buffer: Buffer<T>
 ) : BufferedNDElement<T, R>(), RingElement<NDBuffer<T>, BufferedNDRingElement<T, R>, BufferedNDRing<T, R>> {
-
     override fun unwrap(): NDBuffer<T> = this
 
     override fun NDBuffer<T>.wrap(): BufferedNDRingElement<T, R> {
@@ -43,7 +42,6 @@ class BufferedNDFieldElement<T, F : Field<T>>(
     override val context: BufferedNDField<T, F>,
     override val buffer: Buffer<T>
 ) : BufferedNDElement<T, F>(), FieldElement<NDBuffer<T>, BufferedNDFieldElement<T, F>, BufferedNDField<T, F>> {
-
     override fun unwrap(): NDBuffer<T> = this
 
     override fun NDBuffer<T>.wrap(): BufferedNDFieldElement<T, F> {
@@ -54,9 +52,9 @@ class BufferedNDFieldElement<T, F : Field<T>>(
 
 
 /**
- * Element by element application of any operation on elements to the whole array. Just like in numpy
+ * Element by element application of any operation on elements to the whole array. Just like in numpy.
  */
-operator fun <T : Any, F : Field<T>> Function1<T, T>.invoke(ndElement: BufferedNDElement<T, F>) =
+operator fun <T : Any, F : Field<T>> Function1<T, T>.invoke(ndElement: BufferedNDElement<T, F>): MathElement<out BufferedNDAlgebra<T, F>> =
     ndElement.context.run { map(ndElement) { invoke(it) }.toElement() }
 
 /* plus and minus */
@@ -64,13 +62,13 @@ operator fun <T : Any, F : Field<T>> Function1<T, T>.invoke(ndElement: BufferedN
 /**
  * Summation operation for [BufferedNDElement] and single element
  */
-operator fun <T : Any, F : Space<T>> BufferedNDElement<T, F>.plus(arg: T) =
+operator fun <T : Any, F : Space<T>> BufferedNDElement<T, F>.plus(arg: T): NDElement<T, F, NDBuffer<T>> =
     context.map(this) { it + arg }.wrap()
 
 /**
  * Subtraction operation between [BufferedNDElement] and single element
  */
-operator fun <T : Any, F : Space<T>> BufferedNDElement<T, F>.minus(arg: T) =
+operator fun <T : Any, F : Space<T>> BufferedNDElement<T, F>.minus(arg: T): NDElement<T, F, NDBuffer<T>> =
     context.map(this) { it - arg }.wrap()
 
 /* prod and div */
@@ -78,11 +76,11 @@ operator fun <T : Any, F : Space<T>> BufferedNDElement<T, F>.minus(arg: T) =
 /**
  * Product operation for [BufferedNDElement] and single element
  */
-operator fun <T : Any, F : Ring<T>> BufferedNDElement<T, F>.times(arg: T) =
+operator fun <T : Any, F : Ring<T>> BufferedNDElement<T, F>.times(arg: T): NDElement<T, F, NDBuffer<T>> =
     context.map(this) { it * arg }.wrap()
 
 /**
  * Division operation between [BufferedNDElement] and single element
  */
-operator fun <T : Any, F : Field<T>> BufferedNDElement<T, F>.div(arg: T) =
+operator fun <T : Any, F : Field<T>> BufferedNDElement<T, F>.div(arg: T): NDElement<T, F, NDBuffer<T>> =
     context.map(this) { it / arg }.wrap()

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/Buffers.kt

@@ -2,41 +2,52 @@ package scientifik.kmath.structures
 
 import scientifik.kmath.operations.Complex
 import scientifik.kmath.operations.complex
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 import kotlin.reflect.KClass
 
-
+/**
+ * Function that produces [Buffer] from its size and function that supplies values.
+ *
+ * @param T the type of buffer.
+ */
 typealias BufferFactory<T> = (Int, (Int) -> T) -> Buffer<T>
-typealias MutableBufferFactory<T> = (Int, (Int) -> T) -> MutableBuffer<T>
-
 
 /**
- * A generic random access structure for both primitives and objects
+ * Function that produces [MutableBuffer] from its size and function that supplies values.
+ *
+ * @param T the type of buffer.
+ */
+typealias MutableBufferFactory<T> = (Int, (Int) -> T) -> MutableBuffer<T>
+
+/**
+ * A generic immutable random-access structure for both primitives and objects.
+ *
+ * @param T the type of elements contained in the buffer.
  */
 interface Buffer<T> {
-
     /**
-     * The size of the buffer
+     * The size of this buffer.
      */
     val size: Int
 
     /**
-     * Get element at given index
+     * Gets element at given index.
      */
     operator fun get(index: Int): T
 
     /**
-     * Iterate over all elements
+     * Iterates over all elements.
      */
     operator fun iterator(): Iterator<T>
 
     /**
-     * Check content eqiality with another buffer
+     * Checks content equality with another buffer.
      */
     fun contentEquals(other: Buffer<*>): Boolean =
         asSequence().mapIndexed { index, value -> value == other[index] }.all { it }
 
     companion object {
-
         inline fun real(size: Int, initializer: (Int) -> Double): RealBuffer {
             val array = DoubleArray(size) { initializer(it) }
             return RealBuffer(array)
@@ -69,17 +80,34 @@ interface Buffer<T> {
     }
 }
 
+/**
+ * Creates a sequence that returns all elements from this [Buffer].
+ */
 fun <T> Buffer<T>.asSequence(): Sequence<T> = Sequence(::iterator)
 
+/**
+ * Creates an iterable that returns all elements from this [Buffer].
+ */
 fun <T> Buffer<T>.asIterable(): Iterable<T> = Iterable(::iterator)
 
-val Buffer<*>.indices: IntRange get() = IntRange(0, size - 1)
+/**
+ * Returns an [IntRange] of the valid indices for this [Buffer].
+ */
+val Buffer<*>.indices: IntRange get() = 0 until size
 
+/**
+ * A generic mutable random-access structure for both primitives and objects.
+ *
+ * @param T the type of elements contained in the buffer.
+ */
 interface MutableBuffer<T> : Buffer<T> {
+    /**
+     * Sets the array element at the specified [index] to the specified [value].
+     */
     operator fun set(index: Int, value: T)
 
     /**
-     * A shallow copy of the buffer
+     * Returns a shallow copy of the buffer.
      */
     fun copy(): MutableBuffer<T>
 
@@ -91,15 +119,14 @@ interface MutableBuffer<T> : Buffer<T> {
             MutableListBuffer(MutableList(size, initializer))
 
         @Suppress("UNCHECKED_CAST")
-        inline fun <T : Any> auto(type: KClass<out T>, size: Int, initializer: (Int) -> T): MutableBuffer<T> {
-            return when (type) {
+        inline fun <T : Any> auto(type: KClass<out T>, size: Int, initializer: (Int) -> T): MutableBuffer<T> =
+            when (type) {
                 Double::class -> RealBuffer(DoubleArray(size) { initializer(it) as Double }) as MutableBuffer<T>
                 Short::class -> ShortBuffer(ShortArray(size) { initializer(it) as Short }) as MutableBuffer<T>
                 Int::class -> IntBuffer(IntArray(size) { initializer(it) as Int }) as MutableBuffer<T>
                 Long::class -> LongBuffer(LongArray(size) { initializer(it) as Long }) as MutableBuffer<T>
                 else -> boxing(size, initializer)
             }
-        }
 
         /**
          * Create most appropriate mutable buffer for given type avoiding boxing wherever possible
@@ -114,73 +141,110 @@ interface MutableBuffer<T> : Buffer<T> {
     }
 }
 
+/**
+ * [Buffer] implementation over [List].
+ *
+ * @param T the type of elements contained in the buffer.
+ * @property list The underlying list.
+ */
 inline class ListBuffer<T>(val list: List<T>) : Buffer<T> {
-
     override val size: Int
         get() = list.size
 
-    override fun get(index: Int): T = list[index]
-
-    override fun iterator(): Iterator<T> = list.iterator()
-}
-
-fun <T> List<T>.asBuffer() = ListBuffer<T>(this)
-
-@Suppress("FunctionName")
-inline fun <T> ListBuffer(size: Int, init: (Int) -> T) = List(size, init).asBuffer()
-
-inline class MutableListBuffer<T>(val list: MutableList<T>) : MutableBuffer<T> {
-
-    override val size: Int
-        get() = list.size
-
-    override fun get(index: Int): T = list[index]
-
-    override fun set(index: Int, value: T) {
-        list[index] = value
-    }
-
-    override fun iterator(): Iterator<T> = list.iterator()
-    override fun copy(): MutableBuffer<T> = MutableListBuffer(ArrayList(list))
-}
-
-class ArrayBuffer<T>(private val array: Array<T>) : MutableBuffer<T> {
-    //Can't inline because array is invariant
-    override val size: Int
-        get() = array.size
-
-    override fun get(index: Int): T = array[index]
-
-    override fun set(index: Int, value: T) {
-        array[index] = value
-    }
-
-    override fun iterator(): Iterator<T> = array.iterator()
-
-    override fun copy(): MutableBuffer<T> = ArrayBuffer(array.copyOf())
-}
-
-fun <T> Array<T>.asBuffer(): ArrayBuffer<T> = ArrayBuffer(this)
-
-inline class ReadOnlyBuffer<T>(val buffer: MutableBuffer<T>) : Buffer<T> {
-    override val size: Int get() = buffer.size
-
-    override fun get(index: Int): T = buffer.get(index)
-
-    override fun iterator() = buffer.iterator()
+    override operator fun get(index: Int): T = list[index]
+    override operator fun iterator(): Iterator<T> = list.iterator()
 }
 
 /**
- * A buffer with content calculated on-demand. The calculated contect is not stored, so it is recalculated on each call.
+ * Returns an [ListBuffer] that wraps the original list.
+ */
+fun <T> List<T>.asBuffer(): ListBuffer<T> = ListBuffer(this)
+
+/**
+ * Creates a new [ListBuffer] with the specified [size], where each element is calculated by calling the specified
+ * [init] function.
+ *
+ * The function [init] is called for each array element sequentially starting from the first one.
+ * It should return the value for an array element given its index.
+ */
+inline fun <T> ListBuffer(size: Int, init: (Int) -> T): ListBuffer<T> {
+    contract { callsInPlace(init) }
+    return List(size, init).asBuffer()
+}
+
+/**
+ * [MutableBuffer] implementation over [MutableList].
+ *
+ * @param T the type of elements contained in the buffer.
+ * @property list The underlying list.
+ */
+inline class MutableListBuffer<T>(val list: MutableList<T>) : MutableBuffer<T> {
+    override val size: Int
+        get() = list.size
+
+    override operator fun get(index: Int): T = list[index]
+
+    override operator fun set(index: Int, value: T) {
+        list[index] = value
+    }
+
+    override operator fun iterator(): Iterator<T> = list.iterator()
+    override fun copy(): MutableBuffer<T> = MutableListBuffer(ArrayList(list))
+}
+
+/**
+ * [MutableBuffer] implementation over [Array].
+ *
+ * @param T the type of elements contained in the buffer.
+ * @property array The underlying array.
+ */
+class ArrayBuffer<T>(private val array: Array<T>) : MutableBuffer<T> {
+    // Can't inline because array is invariant
+    override val size: Int
+        get() = array.size
+
+    override operator fun get(index: Int): T = array[index]
+
+    override operator fun set(index: Int, value: T) {
+        array[index] = value
+    }
+
+    override operator fun iterator(): Iterator<T> = array.iterator()
+    override fun copy(): MutableBuffer<T> = ArrayBuffer(array.copyOf())
+}
+
+/**
+ * Returns an [ArrayBuffer] that wraps the original array.
+ */
+fun <T> Array<T>.asBuffer(): ArrayBuffer<T> = ArrayBuffer(this)
+
+/**
+ * Immutable wrapper for [MutableBuffer].
+ *
+ * @param T the type of elements contained in the buffer.
+ * @property buffer The underlying buffer.
+ */
+inline class ReadOnlyBuffer<T>(val buffer: MutableBuffer<T>) : Buffer<T> {
+    override val size: Int get() = buffer.size
+
+    override operator fun get(index: Int): T = buffer[index]
+
+    override operator fun iterator(): Iterator<T> = buffer.iterator()
+}
+
+/**
+ * A buffer with content calculated on-demand. The calculated content is not stored, so it is recalculated on each call.
  * Useful when one needs single element from the buffer.
+ *
+ * @param T the type of elements provided by the buffer.
  */
 class VirtualBuffer<T>(override val size: Int, private val generator: (Int) -> T) : Buffer<T> {
-    override fun get(index: Int): T {
+    override operator fun get(index: Int): T {
         if (index < 0 || index >= size) throw IndexOutOfBoundsException("Expected index from 0 to ${size - 1}, but found $index")
         return generator(index)
     }
 
-    override fun iterator(): Iterator<T> = (0 until size).asSequence().map(generator).iterator()
+    override operator fun iterator(): Iterator<T> = (0 until size).asSequence().map(generator).iterator()
 
     override fun contentEquals(other: Buffer<*>): Boolean {
         return if (other is VirtualBuffer) {
@@ -192,17 +256,16 @@ class VirtualBuffer<T>(override val size: Int, private val generator: (Int) -> T
 }
 
 /**
- * Convert this buffer to read-only buffer
+ * Convert this buffer to read-only buffer.
  */
-fun <T> Buffer<T>.asReadOnly(): Buffer<T> = if (this is MutableBuffer) {
-    ReadOnlyBuffer(this)
-} else {
-    this
-}
+fun <T> Buffer<T>.asReadOnly(): Buffer<T> = if (this is MutableBuffer) ReadOnlyBuffer(this) else this
 
 /**
- * Typealias for buffer transformations
+ * Typealias for buffer transformations.
  */
 typealias BufferTransform<T, R> = (Buffer<T>) -> Buffer<R>
 
+/**
+ * Typealias for buffer transformations with suspend function.
+ */
 typealias SuspendBufferTransform<T, R> = suspend (Buffer<T>) -> Buffer<R>

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/ComplexNDField.kt

@@ -4,6 +4,9 @@ import scientifik.kmath.operations.Complex
 import scientifik.kmath.operations.ComplexField
 import scientifik.kmath.operations.FieldElement
 import scientifik.kmath.operations.complex
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 
 typealias ComplexNDElement = BufferedNDFieldElement<Complex, ComplexField>
 
@@ -15,10 +18,9 @@ class ComplexNDField(override val shape: IntArray) :
     ExtendedNDField<Complex, ComplexField, NDBuffer<Complex>> {
 
     override val strides: Strides = DefaultStrides(shape)
-
     override val elementContext: ComplexField get() = ComplexField
-    override val zero by lazy { produce { zero } }
-    override val one by lazy { produce { one } }
+    override val zero: ComplexNDElement by lazy { produce { zero } }
+    override val one: ComplexNDElement by lazy { produce { one } }
 
     inline fun buildBuffer(size: Int, crossinline initializer: (Int) -> Complex): Buffer<Complex> =
         Buffer.complex(size) { initializer(it) }
@@ -45,6 +47,7 @@ class ComplexNDField(override val shape: IntArray) :
         transform: ComplexField.(index: IntArray, Complex) -> Complex
     ): ComplexNDElement {
         check(arg)
+
         return BufferedNDFieldElement(
             this,
             buildBuffer(arg.strides.linearSize) { offset ->
@@ -61,6 +64,7 @@ class ComplexNDField(override val shape: IntArray) :
         transform: ComplexField.(Complex, Complex) -> Complex
     ): ComplexNDElement {
         check(a, b)
+
         return BufferedNDFieldElement(
             this,
             buildBuffer(strides.linearSize) { offset -> elementContext.transform(a.buffer[offset], b.buffer[offset]) })
@@ -69,23 +73,25 @@ class ComplexNDField(override val shape: IntArray) :
     override fun NDBuffer<Complex>.toElement(): FieldElement<NDBuffer<Complex>, *, out BufferedNDField<Complex, ComplexField>> =
         BufferedNDFieldElement(this@ComplexNDField, buffer)
 
-    override fun power(arg: NDBuffer<Complex>, pow: Number) = map(arg) { power(it, pow) }
+    override fun power(arg: NDBuffer<Complex>, pow: Number): ComplexNDElement =
+        map(arg) { power(it, pow) }
 
-    override fun exp(arg: NDBuffer<Complex>) = map(arg) { exp(it) }
+    override fun exp(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { exp(it) }
+    override fun ln(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { ln(it) }
 
-    override fun ln(arg: NDBuffer<Complex>) = map(arg) { ln(it) }
+    override fun sin(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { sin(it) }
+    override fun cos(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { cos(it) }
+    override fun tan(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { tan(it) }
+    override fun asin(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { asin(it) }
+    override fun acos(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { acos(it) }
+    override fun atan(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { atan(it) }
 
-    override fun sin(arg: NDBuffer<Complex>) = map(arg) { sin(it) }
-
-    override fun cos(arg: NDBuffer<Complex>) = map(arg) { cos(it) }
-
-    override fun tan(arg: NDBuffer<Complex>): NDBuffer<Complex> = map(arg) { tan(it) }
-
-    override fun asin(arg: NDBuffer<Complex>): NDBuffer<Complex> = map(arg) { asin(it) }
-
-    override fun acos(arg: NDBuffer<Complex>): NDBuffer<Complex> = map(arg) {acos(it)}
-
-    override fun atan(arg: NDBuffer<Complex>): NDBuffer<Complex> = map(arg) {atan(it)}
+    override fun sinh(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { sinh(it) }
+    override fun cosh(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { cosh(it) }
+    override fun tanh(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { tanh(it) }
+    override fun asinh(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { asinh(it) }
+    override fun acosh(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { acosh(it) }
+    override fun atanh(arg: NDBuffer<Complex>): ComplexNDElement = map(arg) { atanh(it) }
 }
 
 
@@ -98,15 +104,16 @@ inline fun BufferedNDField<Complex, ComplexField>.produceInline(crossinline init
 }
 
 /**
- * Map one [ComplexNDElement] using function with indexes
+ * Map one [ComplexNDElement] using function with indices.
  */
-inline fun ComplexNDElement.mapIndexed(crossinline transform: ComplexField.(index: IntArray, Complex) -> Complex) =
+inline fun ComplexNDElement.mapIndexed(crossinline transform: ComplexField.(index: IntArray, Complex) -> Complex): ComplexNDElement =
     context.produceInline { offset -> transform(strides.index(offset), buffer[offset]) }
 
 /**
- * Map one [ComplexNDElement] using function without indexes
+ * Map one [ComplexNDElement] using function without indices.
  */
 inline fun ComplexNDElement.map(crossinline transform: ComplexField.(Complex) -> Complex): ComplexNDElement {
+    contract { callsInPlace(transform) }
     val buffer = Buffer.complex(strides.linearSize) { offset -> ComplexField.transform(buffer[offset]) }
     return BufferedNDFieldElement(context, buffer)
 }
@@ -114,7 +121,7 @@ inline fun ComplexNDElement.map(crossinline transform: ComplexField.(Complex) ->
 /**
  * Element by element application of any operation on elements to the whole array. Just like in numpy
  */
-operator fun Function1<Complex, Complex>.invoke(ndElement: ComplexNDElement) =
+operator fun Function1<Complex, Complex>.invoke(ndElement: ComplexNDElement): ComplexNDElement =
     ndElement.map { this@invoke(it) }
 
 
@@ -123,19 +130,18 @@ operator fun Function1<Complex, Complex>.invoke(ndElement: ComplexNDElement) =
 /**
  * Summation operation for [BufferedNDElement] and single element
  */
-operator fun ComplexNDElement.plus(arg: Complex) =
-    map { it + arg }
+operator fun ComplexNDElement.plus(arg: Complex): ComplexNDElement = map { it + arg }
 
 /**
  * Subtraction operation between [BufferedNDElement] and single element
  */
-operator fun ComplexNDElement.minus(arg: Complex) =
+operator fun ComplexNDElement.minus(arg: Complex): ComplexNDElement =
     map { it - arg }
 
-operator fun ComplexNDElement.plus(arg: Double) =
+operator fun ComplexNDElement.plus(arg: Double): ComplexNDElement =
     map { it + arg }
 
-operator fun ComplexNDElement.minus(arg: Double) =
+operator fun ComplexNDElement.minus(arg: Double): ComplexNDElement =
     map { it - arg }
 
 fun NDField.Companion.complex(vararg shape: Int): ComplexNDField = ComplexNDField(shape)
@@ -147,5 +153,6 @@ fun NDElement.Companion.complex(vararg shape: Int, initializer: ComplexField.(In
  * Produce a context for n-dimensional operations inside this real field
  */
 inline fun <R> ComplexField.nd(vararg shape: Int, action: ComplexNDField.() -> R): R {
-    return NDField.complex(*shape).run(action)
+    contract { callsInPlace(action, InvocationKind.EXACTLY_ONCE) }
+    return NDField.complex(*shape).action()
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/ExtendedNDField.kt

@@ -2,9 +2,15 @@ package scientifik.kmath.structures
 
 import scientifik.kmath.operations.ExtendedField
 
+/**
+ * [ExtendedField] over [NDStructure].
+ *
+ * @param T the type of the element contained in ND structure.
+ * @param N the type of ND structure.
+ * @param F the extended field of structure elements.
+ */
 interface ExtendedNDField<T : Any, F : ExtendedField<T>, N : NDStructure<T>> : NDField<T, F, N>, ExtendedField<N>
 
-
 ///**
 // * NDField that supports [ExtendedField] operations on its elements
 // */
@@ -36,5 +42,3 @@ interface ExtendedNDField<T : Any, F : ExtendedField<T>, N : NDStructure<T>> : N
 //        return produce { with(elementContext) { cos(arg[it]) } }
 //    }
 //}
-
-

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/FlaggedBuffer.kt

@@ -1,16 +1,38 @@
 package scientifik.kmath.structures
 
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 import kotlin.experimental.and
 
+/**
+ * Represents flags to supply additional info about values of buffer.
+ *
+ * @property mask bit mask value of this flag.
+ */
 enum class ValueFlag(val mask: Byte) {
+    /**
+     * Reports the value is NaN.
+     */
     NAN(0b0000_0001),
+
+    /**
+     * Reports the value doesn't present in the buffer (when the type of value doesn't support `null`).
+     */
     MISSING(0b0000_0010),
+
+    /**
+     * Reports the value is negative infinity.
+     */
     NEGATIVE_INFINITY(0b0000_0100),
+
+    /**
+     * Reports the value is positive infinity
+     */
     POSITIVE_INFINITY(0b0000_1000)
 }
 
 /**
- * A buffer with flagged values
+ * A buffer with flagged values.
  */
 interface FlaggedBuffer<T> : Buffer<T> {
     fun getFlag(index: Int): Byte
@@ -19,11 +41,11 @@ interface FlaggedBuffer<T> : Buffer<T> {
 /**
  * The value is valid if all flags are down
  */
-fun FlaggedBuffer<*>.isValid(index: Int) = getFlag(index) != 0.toByte()
+fun FlaggedBuffer<*>.isValid(index: Int): Boolean = getFlag(index) != 0.toByte()
 
-fun FlaggedBuffer<*>.hasFlag(index: Int, flag: ValueFlag) = (getFlag(index) and flag.mask) != 0.toByte()
+fun FlaggedBuffer<*>.hasFlag(index: Int, flag: ValueFlag): Boolean = (getFlag(index) and flag.mask) != 0.toByte()
 
-fun FlaggedBuffer<*>.isMissing(index: Int) = hasFlag(index, ValueFlag.MISSING)
+fun FlaggedBuffer<*>.isMissing(index: Int): Boolean = hasFlag(index, ValueFlag.MISSING)
 
 /**
  * A real buffer which supports flags for each value like NaN or Missing
@@ -37,17 +59,18 @@ class FlaggedRealBuffer(val values: DoubleArray, val flags: ByteArray) : Flagged
 
     override val size: Int get() = values.size
 
-    override fun get(index: Int): Double? = if (isValid(index)) values[index] else null
+    override operator fun get(index: Int): Double? = if (isValid(index)) values[index] else null
 
-    override fun iterator(): Iterator<Double?> = values.indices.asSequence().map {
+    override operator fun iterator(): Iterator<Double?> = values.indices.asSequence().map {
         if (isValid(it)) values[it] else null
     }.iterator()
 }
 
 inline fun FlaggedRealBuffer.forEachValid(block: (Double) -> Unit) {
-    for(i in indices){
-        if(isValid(i)){
-            block(values[i])
-        }
-    }
+    contract { callsInPlace(block) }
+
+    indices
+        .asSequence()
+        .filter(::isValid)
+        .forEach { block(values[it]) }
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/FloatBuffer.kt

@@ -0,0 +1,55 @@
+package scientifik.kmath.structures
+
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
+
+/**
+ * Specialized [MutableBuffer] implementation over [FloatArray].
+ *
+ * @property array the underlying array.
+ */
+inline class FloatBuffer(val array: FloatArray) : MutableBuffer<Float> {
+    override val size: Int get() = array.size
+
+    override operator fun get(index: Int): Float = array[index]
+
+    override operator fun set(index: Int, value: Float) {
+        array[index] = value
+    }
+
+    override operator fun iterator(): FloatIterator = array.iterator()
+
+    override fun copy(): MutableBuffer<Float> =
+        FloatBuffer(array.copyOf())
+}
+
+/**
+ * Creates a new [FloatBuffer] with the specified [size], where each element is calculated by calling the specified
+ * [init] function.
+ *
+ * The function [init] is called for each array element sequentially starting from the first one.
+ * It should return the value for an buffer element given its index.
+ */
+inline fun FloatBuffer(size: Int, init: (Int) -> Float): FloatBuffer {
+    contract { callsInPlace(init) }
+    return FloatBuffer(FloatArray(size) { init(it) })
+}
+
+/**
+ * Returns a new [FloatBuffer] of given elements.
+ */
+fun FloatBuffer(vararg floats: Float): FloatBuffer = FloatBuffer(floats)
+
+/**
+ * Returns a [FloatArray] containing all of the elements of this [MutableBuffer].
+ */
+val MutableBuffer<out Float>.array: FloatArray
+    get() = (if (this is FloatBuffer) array else FloatArray(size) { get(it) })
+
+/**
+ * Returns [FloatBuffer] over this array.
+ *
+ * @receiver the array.
+ * @return the new buffer.
+ */
+fun FloatArray.asBuffer(): FloatBuffer = FloatBuffer(this)

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/IntBuffer.kt

@@ -1,20 +1,56 @@
 package scientifik.kmath.structures
 
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
+
+/**
+ * Specialized [MutableBuffer] implementation over [IntArray].
+ *
+ * @property array the underlying array.
+ */
 inline class IntBuffer(val array: IntArray) : MutableBuffer<Int> {
     override val size: Int get() = array.size
 
-    override fun get(index: Int): Int = array[index]
+    override operator fun get(index: Int): Int = array[index]
 
-    override fun set(index: Int, value: Int) {
+    override operator fun set(index: Int, value: Int) {
         array[index] = value
     }
 
-    override fun iterator() = array.iterator()
+    override operator fun iterator(): IntIterator = array.iterator()
 
     override fun copy(): MutableBuffer<Int> =
         IntBuffer(array.copyOf())
-
 }
 
+/**
+ * Creates a new [IntBuffer] with the specified [size], where each element is calculated by calling the specified
+ * [init] function.
+ *
+ * The function [init] is called for each array element sequentially starting from the first one.
+ * It should return the value for an buffer element given its index.
+ */
+inline fun IntBuffer(size: Int, init: (Int) -> Int): IntBuffer {
+    contract { callsInPlace(init) }
+    return IntBuffer(IntArray(size) { init(it) })
+}
 
-fun IntArray.asBuffer() = IntBuffer(this)
+/**
+ * Returns a new [IntBuffer] of given elements.
+ */
+fun IntBuffer(vararg ints: Int): IntBuffer = IntBuffer(ints)
+
+/**
+ * Returns a [IntArray] containing all of the elements of this [MutableBuffer].
+ */
+val MutableBuffer<out Int>.array: IntArray
+    get() = (if (this is IntBuffer) array else IntArray(size) { get(it) })
+
+/**
+ * Returns [IntBuffer] over this array.
+ *
+ * @receiver the array.
+ * @return the new buffer.
+ */
+fun IntArray.asBuffer(): IntBuffer = IntBuffer(this)

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/LongBuffer.kt

@@ -1,19 +1,56 @@
 package scientifik.kmath.structures
 
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
+
+/**
+ * Specialized [MutableBuffer] implementation over [LongArray].
+ *
+ * @property array the underlying array.
+ */
 inline class LongBuffer(val array: LongArray) : MutableBuffer<Long> {
     override val size: Int get() = array.size
 
-    override fun get(index: Int): Long = array[index]
+    override operator fun get(index: Int): Long = array[index]
 
-    override fun set(index: Int, value: Long) {
+    override operator fun set(index: Int, value: Long) {
         array[index] = value
     }
 
-    override fun iterator() = array.iterator()
+    override operator fun iterator(): LongIterator = array.iterator()
 
     override fun copy(): MutableBuffer<Long> =
         LongBuffer(array.copyOf())
 
 }
 
-fun LongArray.asBuffer() = LongBuffer(this)
+/**
+ * Creates a new [LongBuffer] with the specified [size], where each element is calculated by calling the specified
+ * [init] function.
+ *
+ * The function [init] is called for each array element sequentially starting from the first one.
+ * It should return the value for an buffer element given its index.
+ */
+inline fun LongBuffer(size: Int, init: (Int) -> Long): LongBuffer {
+    contract { callsInPlace(init) }
+    return LongBuffer(LongArray(size) { init(it) })
+}
+
+/**
+ * Returns a new [LongBuffer] of given elements.
+ */
+fun LongBuffer(vararg longs: Long): LongBuffer = LongBuffer(longs)
+
+/**
+ * Returns a [IntArray] containing all of the elements of this [MutableBuffer].
+ */
+val MutableBuffer<out Long>.array: LongArray
+    get() = (if (this is LongBuffer) array else LongArray(size) { get(it) })
+
+/**
+ * Returns [LongBuffer] over this array.
+ *
+ * @receiver the array.
+ * @return the new buffer.
+ */
+fun LongArray.asBuffer(): LongBuffer = LongBuffer(this)

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/MemoryBuffer.kt

@@ -3,21 +3,22 @@ package scientifik.kmath.structures
 import scientifik.memory.*
 
 /**
- * A non-boxing buffer based on [ByteBuffer] storage
+ * A non-boxing buffer over [Memory] object.
+ *
+ * @param T the type of elements contained in the buffer.
+ * @property memory the underlying memory segment.
+ * @property spec the spec of [T] type.
  */
 open class MemoryBuffer<T : Any>(protected val memory: Memory, protected val spec: MemorySpec<T>) : Buffer<T> {
-
     override val size: Int get() = memory.size / spec.objectSize
 
-    private val reader = memory.reader()
-
-    override fun get(index: Int): T = reader.read(spec, spec.objectSize * index)
-
-    override fun iterator(): Iterator<T> = (0 until size).asSequence().map { get(it) }.iterator()
+    private val reader: MemoryReader = memory.reader()
 
+    override operator fun get(index: Int): T = reader.read(spec, spec.objectSize * index)
+    override operator fun iterator(): Iterator<T> = (0 until size).asSequence().map { get(it) }.iterator()
 
     companion object {
-        fun <T : Any> create(spec: MemorySpec<T>, size: Int) =
+        fun <T : Any> create(spec: MemorySpec<T>, size: Int): MemoryBuffer<T> =
             MemoryBuffer(Memory.allocate(size * spec.objectSize), spec)
 
         inline fun <T : Any> create(
@@ -33,24 +34,30 @@ open class MemoryBuffer<T : Any>(protected val memory: Memory, protected val spe
     }
 }
 
+/**
+ * A mutable non-boxing buffer over [Memory] object.
+ *
+ * @param T the type of elements contained in the buffer.
+ * @property memory the underlying memory segment.
+ * @property spec the spec of [T] type.
+ */
 class MutableMemoryBuffer<T : Any>(memory: Memory, spec: MemorySpec<T>) : MemoryBuffer<T>(memory, spec),
     MutableBuffer<T> {
 
-    private val writer = memory.writer()
-
-    override fun set(index: Int, value: T) = writer.write(spec, spec.objectSize * index, value)
+    private val writer: MemoryWriter = memory.writer()
 
+    override operator fun set(index: Int, value: T): Unit = writer.write(spec, spec.objectSize * index, value)
     override fun copy(): MutableBuffer<T> = MutableMemoryBuffer(memory.copy(), spec)
 
     companion object {
-        fun <T : Any> create(spec: MemorySpec<T>, size: Int) =
+        fun <T : Any> create(spec: MemorySpec<T>, size: Int): MutableMemoryBuffer<T> =
             MutableMemoryBuffer(Memory.allocate(size * spec.objectSize), spec)
 
         inline fun <T : Any> create(
             spec: MemorySpec<T>,
             size: Int,
             crossinline initializer: (Int) -> T
-        ) =
+        ): MutableMemoryBuffer<T> =
             MutableMemoryBuffer(Memory.allocate(size * spec.objectSize), spec).also { buffer ->
                 (0 until size).forEach {
                     buffer[it] = initializer(it)

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/NDAlgebra.kt

@@ -56,7 +56,7 @@ interface NDAlgebra<T, C, N : NDStructure<T>> {
     /**
      * element-by-element invoke a function working on [T] on a [NDStructure]
      */
-    operator fun Function1<T, T>.invoke(structure: N) = map(structure) { value -> this@invoke(value) }
+    operator fun Function1<T, T>.invoke(structure: N): N = map(structure) { value -> this@invoke(value) }
 
     companion object
 }
@@ -76,12 +76,12 @@ interface NDSpace<T, S : Space<T>, N : NDStructure<T>> : Space<N>, NDAlgebra<T,
     override fun multiply(a: N, k: Number): N = map(a) { multiply(it, k) }
 
     //TODO move to extensions after KEEP-176
-    operator fun N.plus(arg: T) = map(this) { value -> add(arg, value) }
+    operator fun N.plus(arg: T): N = map(this) { value -> add(arg, value) }
 
-    operator fun N.minus(arg: T) = map(this) { value -> add(arg, -value) }
+    operator fun N.minus(arg: T): N = map(this) { value -> add(arg, -value) }
 
-    operator fun T.plus(arg: N) = map(arg) { value -> add(this@plus, value) }
-    operator fun T.minus(arg: N) = map(arg) { value -> add(-this@minus, value) }
+    operator fun T.plus(arg: N): N = map(arg) { value -> add(this@plus, value) }
+    operator fun T.minus(arg: N): N = map(arg) { value -> add(-this@minus, value) }
 
     companion object
 }
@@ -97,20 +97,19 @@ interface NDRing<T, R : Ring<T>, N : NDStructure<T>> : Ring<N>, NDSpace<T, R, N>
     override fun multiply(a: N, b: N): N = combine(a, b) { aValue, bValue -> multiply(aValue, bValue) }
 
     //TODO move to extensions after KEEP-176
-    operator fun N.times(arg: T) = map(this) { value -> multiply(arg, value) }
+    operator fun N.times(arg: T): N = map(this) { value -> multiply(arg, value) }
 
-    operator fun T.times(arg: N) = map(arg) { value -> multiply(this@times, value) }
+    operator fun T.times(arg: N): N = map(arg) { value -> multiply(this@times, value) }
 
     companion object
 }
 
 /**
- * Field for n-dimensional structures.
- * @param shape - the list of dimensions of the array
- * @param elementField - operations field defined on individual array element
- * @param T - the type of the element contained in ND structure
- * @param F - field of structure elements
- * @param R - actual nd-element type of this field
+ * Field of [NDStructure].
+ *
+ * @param T the type of the element contained in ND structure.
+ * @param N the type of ND structure.
+ * @param F field of structure elements.
  */
 interface NDField<T, F : Field<T>, N : NDStructure<T>> : Field<N>, NDRing<T, F, N> {
 
@@ -120,9 +119,9 @@ interface NDField<T, F : Field<T>, N : NDStructure<T>> : Field<N>, NDRing<T, F,
     override fun divide(a: N, b: N): N = combine(a, b) { aValue, bValue -> divide(aValue, bValue) }
 
     //TODO move to extensions after KEEP-176
-    operator fun N.div(arg: T) = map(this) { value -> divide(arg, value) }
+    operator fun N.div(arg: T): N = map(this) { value -> divide(arg, value) }
 
-    operator fun T.div(arg: N) = map(arg) { divide(it, this@div) }
+    operator fun T.div(arg: N): N = map(arg) { divide(it, this@div) }
 
     companion object {
 
@@ -131,7 +130,7 @@ interface NDField<T, F : Field<T>, N : NDStructure<T>> : Field<N>, NDRing<T, F,
         /**
          * Create a nd-field for [Double] values or pull it from cache if it was created previously
          */
-        fun real(vararg shape: Int) = realNDFieldCache.getOrPut(shape) { RealNDField(shape) }
+        fun real(vararg shape: Int): RealNDField = realNDFieldCache.getOrPut(shape) { RealNDField(shape) }
 
         /**
          * Create a nd-field with boxing generic buffer
@@ -140,7 +139,7 @@ interface NDField<T, F : Field<T>, N : NDStructure<T>> : Field<N>, NDRing<T, F,
             field: F,
             vararg shape: Int,
             bufferFactory: BufferFactory<T> = Buffer.Companion::boxing
-        ) = BoxingNDField(shape, field, bufferFactory)
+        ): BoxingNDField<T, F> = BoxingNDField(shape, field, bufferFactory)
 
         /**
          * Create a most suitable implementation for nd-field using reified class.

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/NDElement.kt

@@ -23,19 +23,24 @@ interface NDElement<T, C, N : NDStructure<T>> : NDStructure<T> {
         /**
          * Create a optimized NDArray of doubles
          */
-        fun real(shape: IntArray, initializer: RealField.(IntArray) -> Double = { 0.0 }) =
+        fun real(shape: IntArray, initializer: RealField.(IntArray) -> Double = { 0.0 }): RealNDElement =
             NDField.real(*shape).produce(initializer)
 
-
-        fun real1D(dim: Int, initializer: (Int) -> Double = { _ -> 0.0 }) =
+        inline fun real1D(dim: Int, crossinline initializer: (Int) -> Double = { _ -> 0.0 }): RealNDElement =
             real(intArrayOf(dim)) { initializer(it[0]) }
 
+        inline fun real2D(
+            dim1: Int,
+            dim2: Int,
+            crossinline initializer: (Int, Int) -> Double = { _, _ -> 0.0 }
+        ): RealNDElement = real(intArrayOf(dim1, dim2)) { initializer(it[0], it[1]) }
 
-        fun real2D(dim1: Int, dim2: Int, initializer: (Int, Int) -> Double = { _, _ -> 0.0 }) =
-            real(intArrayOf(dim1, dim2)) { initializer(it[0], it[1]) }
-
-        fun real3D(dim1: Int, dim2: Int, dim3: Int, initializer: (Int, Int, Int) -> Double = { _, _, _ -> 0.0 }) =
-            real(intArrayOf(dim1, dim2, dim3)) { initializer(it[0], it[1], it[2]) }
+        inline fun real3D(
+            dim1: Int,
+            dim2: Int,
+            dim3: Int,
+            crossinline initializer: (Int, Int, Int) -> Double = { _, _, _ -> 0.0 }
+        ): RealNDElement = real(intArrayOf(dim1, dim2, dim3)) { initializer(it[0], it[1], it[2]) }
 
 
         /**
@@ -62,16 +67,16 @@ interface NDElement<T, C, N : NDStructure<T>> : NDStructure<T> {
 }
 
 
-fun <T, C, N : NDStructure<T>> NDElement<T, C, N>.mapIndexed(transform: C.(index: IntArray, T) -> T) =
+fun <T, C, N : NDStructure<T>> NDElement<T, C, N>.mapIndexed(transform: C.(index: IntArray, T) -> T): NDElement<T, C, N> =
     context.mapIndexed(unwrap(), transform).wrap()
 
-fun <T, C, N : NDStructure<T>> NDElement<T, C, N>.map(transform: C.(T) -> T) = context.map(unwrap(), transform).wrap()
-
+fun <T, C, N : NDStructure<T>> NDElement<T, C, N>.map(transform: C.(T) -> T): NDElement<T, C, N> =
+    context.map(unwrap(), transform).wrap()
 
 /**
  * Element by element application of any operation on elements to the whole [NDElement]
  */
-operator fun <T, C, N : NDStructure<T>> Function1<T, T>.invoke(ndElement: NDElement<T, C, N>) =
+operator fun <T, C, N : NDStructure<T>> Function1<T, T>.invoke(ndElement: NDElement<T, C, N>): NDElement<T, C, N> =
     ndElement.map { value -> this@invoke(value) }
 
 /* plus and minus */
@@ -79,13 +84,13 @@ operator fun <T, C, N : NDStructure<T>> Function1<T, T>.invoke(ndElement: NDElem
 /**
  * Summation operation for [NDElement] and single element
  */
-operator fun <T, S : Space<T>, N : NDStructure<T>> NDElement<T, S, N>.plus(arg: T) =
+operator fun <T, S : Space<T>, N : NDStructure<T>> NDElement<T, S, N>.plus(arg: T): NDElement<T, S, N> =
     map { value -> arg + value }
 
 /**
  * Subtraction operation between [NDElement] and single element
  */
-operator fun <T, S : Space<T>, N : NDStructure<T>> NDElement<T, S, N>.minus(arg: T) =
+operator fun <T, S : Space<T>, N : NDStructure<T>> NDElement<T, S, N>.minus(arg: T): NDElement<T, S, N> =
     map { value -> arg - value }
 
 /* prod and div */
@@ -93,16 +98,15 @@ operator fun <T, S : Space<T>, N : NDStructure<T>> NDElement<T, S, N>.minus(arg:
 /**
  * Product operation for [NDElement] and single element
  */
-operator fun <T, R : Ring<T>, N : NDStructure<T>> NDElement<T, R, N>.times(arg: T) =
+operator fun <T, R : Ring<T>, N : NDStructure<T>> NDElement<T, R, N>.times(arg: T): NDElement<T, R, N> =
     map { value -> arg * value }
 
 /**
  * Division operation between [NDElement] and single element
  */
-operator fun <T, F : Field<T>, N : NDStructure<T>> NDElement<T, F, N>.div(arg: T) =
+operator fun <T, F : Field<T>, N : NDStructure<T>> NDElement<T, F, N>.div(arg: T): NDElement<T, F, N> =
     map { value -> arg / value }
 
-
 //    /**
 //     * Reverse sum operation
 //     */

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/NDStructure.kt

@@ -1,17 +1,42 @@
 package scientifik.kmath.structures
 
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 import kotlin.jvm.JvmName
 import kotlin.reflect.KClass
 
-
+/**
+ * Represents n-dimensional structure, i.e. multidimensional container of items of the same type and size. The number
+ * of dimensions and items in an array is defined by its shape, which is a sequence of non-negative integers that
+ * specify the sizes of each dimension.
+ *
+ * @param T the type of items.
+ */
 interface NDStructure<T> {
-
+    /**
+     * The shape of structure, i.e. non-empty sequence of non-negative integers that specify sizes of dimensions of
+     * this structure.
+     */
     val shape: IntArray
 
-    val dimension get() = shape.size
+    /**
+     * The count of dimensions in this structure. It should be equal to size of [shape].
+     */
+    val dimension: Int get() = shape.size
 
+    /**
+     * Returns the value at the specified indices.
+     *
+     * @param index the indices.
+     * @return the value.
+     */
     operator fun get(index: IntArray): T
 
+    /**
+     * Returns the sequence of all the elements associated by their indices.
+     *
+     * @return the lazy sequence of pairs of indices to values.
+     */
     fun elements(): Sequence<Pair<IntArray, T>>
 
     override fun equals(other: Any?): Boolean
@@ -19,6 +44,9 @@ interface NDStructure<T> {
     override fun hashCode(): Int
 
     companion object {
+        /**
+         * Indicates whether some [NDStructure] is equal to another one.
+         */
         fun equals(st1: NDStructure<*>, st2: NDStructure<*>): Boolean {
             if (st1 === st2) return true
 
@@ -36,58 +64,89 @@ interface NDStructure<T> {
         }
 
         /**
-         * Create a NDStructure with explicit buffer factory
+         * Creates a NDStructure with explicit buffer factory.
          *
-         * Strides should be reused if possible
+         * Strides should be reused if possible.
          */
         fun <T> build(
             strides: Strides,
             bufferFactory: BufferFactory<T> = Buffer.Companion::boxing,
             initializer: (IntArray) -> T
-        ) =
+        ): BufferNDStructure<T> =
             BufferNDStructure(strides, bufferFactory(strides.linearSize) { i -> initializer(strides.index(i)) })
 
         /**
          * Inline create NDStructure with non-boxing buffer implementation if it is possible
          */
-        inline fun <reified T : Any> auto(strides: Strides, crossinline initializer: (IntArray) -> T) =
+        inline fun <reified T : Any> auto(
+            strides: Strides,
+            crossinline initializer: (IntArray) -> T
+        ): BufferNDStructure<T> =
             BufferNDStructure(strides, Buffer.auto(strides.linearSize) { i -> initializer(strides.index(i)) })
 
-        inline fun <T : Any> auto(type: KClass<T>, strides: Strides, crossinline initializer: (IntArray) -> T) =
+        inline fun <T : Any> auto(
+            type: KClass<T>,
+            strides: Strides,
+            crossinline initializer: (IntArray) -> T
+        ): BufferNDStructure<T> =
             BufferNDStructure(strides, Buffer.auto(type, strides.linearSize) { i -> initializer(strides.index(i)) })
 
         fun <T> build(
             shape: IntArray,
             bufferFactory: BufferFactory<T> = Buffer.Companion::boxing,
             initializer: (IntArray) -> T
-        ) = build(DefaultStrides(shape), bufferFactory, initializer)
+        ): BufferNDStructure<T> = build(DefaultStrides(shape), bufferFactory, initializer)
 
-        inline fun <reified T : Any> auto(shape: IntArray, crossinline initializer: (IntArray) -> T) =
+        inline fun <reified T : Any> auto(
+            shape: IntArray,
+            crossinline initializer: (IntArray) -> T
+        ): BufferNDStructure<T> =
             auto(DefaultStrides(shape), initializer)
 
         @JvmName("autoVarArg")
-        inline fun <reified T : Any> auto(vararg shape: Int, crossinline initializer: (IntArray) -> T) =
+        inline fun <reified T : Any> auto(
+            vararg shape: Int,
+            crossinline initializer: (IntArray) -> T
+        ): BufferNDStructure<T> =
             auto(DefaultStrides(shape), initializer)
 
-        inline fun <T : Any> auto(type: KClass<T>, vararg shape: Int, crossinline initializer: (IntArray) -> T) =
+        inline fun <T : Any> auto(
+            type: KClass<T>,
+            vararg shape: Int,
+            crossinline initializer: (IntArray) -> T
+        ): BufferNDStructure<T> =
             auto(type, DefaultStrides(shape), initializer)
     }
 }
 
+/**
+ * Returns the value at the specified indices.
+ *
+ * @param index the indices.
+ * @return the value.
+ */
 operator fun <T> NDStructure<T>.get(vararg index: Int): T = get(index)
 
+/**
+ * Represents mutable [NDStructure].
+ */
 interface MutableNDStructure<T> : NDStructure<T> {
+    /**
+     * Inserts an item at the specified indices.
+     *
+     * @param index the indices.
+     * @param value the value.
+     */
     operator fun set(index: IntArray, value: T)
 }
 
 inline fun <T> MutableNDStructure<T>.mapInPlace(action: (IntArray, T) -> T) {
-    elements().forEach { (index, oldValue) ->
-        this[index] = action(index, oldValue)
-    }
+    contract { callsInPlace(action) }
+    elements().forEach { (index, oldValue) -> this[index] = action(index, oldValue) }
 }
 
 /**
- * A way to convert ND index to linear one and back
+ * A way to convert ND index to linear one and back.
  */
 interface Strides {
     /**
@@ -124,11 +183,14 @@ interface Strides {
     }
 }
 
+/**
+ * Simple implementation of [Strides].
+ */
 class DefaultStrides private constructor(override val shape: IntArray) : Strides {
     /**
      * Strides for memory access
      */
-    override val strides by lazy {
+    override val strides: List<Int> by lazy {
         sequence {
             var current = 1
             yield(1)
@@ -139,14 +201,12 @@ class DefaultStrides private constructor(override val shape: IntArray) : Strides
         }.toList()
     }
 
-    override fun offset(index: IntArray): Int {
-        return index.mapIndexed { i, value ->
-            if (value < 0 || value >= this.shape[i]) {
-                throw RuntimeException("Index $value out of shape bounds: (0,${this.shape[i]})")
-            }
+    override fun offset(index: IntArray): Int = index.mapIndexed { i, value ->
+        if (value < 0 || value >= this.shape[i])
+            throw IndexOutOfBoundsException("Index $value out of shape bounds: (0,${this.shape[i]})")
+
         value * strides[i]
     }.sum()
-    }
 
     override fun index(offset: Int): IntArray {
         val res = IntArray(shape.size)
@@ -163,19 +223,14 @@ class DefaultStrides private constructor(override val shape: IntArray) : Strides
     override val linearSize: Int
         get() = strides[shape.size]
 
-
     override fun equals(other: Any?): Boolean {
         if (this === other) return true
         if (other !is DefaultStrides) return false
-
         if (!shape.contentEquals(other.shape)) return false
-
         return true
     }
 
-    override fun hashCode(): Int {
-        return shape.contentHashCode()
-    }
+    override fun hashCode(): Int = shape.contentHashCode()
 
     companion object {
         private val defaultStridesCache = HashMap<IntArray, Strides>()
@@ -187,11 +242,23 @@ class DefaultStrides private constructor(override val shape: IntArray) : Strides
     }
 }
 
+/**
+ * Represents [NDStructure] over [Buffer].
+ *
+ * @param T the type of items.
+ */
 abstract class NDBuffer<T> : NDStructure<T> {
+    /**
+     * The underlying buffer.
+     */
     abstract val buffer: Buffer<T>
+
+    /**
+     * The strides to access elements of [Buffer] by linear indices.
+     */
     abstract val strides: Strides
 
-    override fun get(index: IntArray): T = buffer[strides.offset(index)]
+    override operator fun get(index: IntArray): T = buffer[strides.offset(index)]
 
     override val shape: IntArray get() = strides.shape
 
@@ -238,7 +305,7 @@ inline fun <T, reified R : Any> NDStructure<T>.mapToBuffer(
 }
 
 /**
- * Mutable ND buffer based on linear [autoBuffer]
+ * Mutable ND buffer based on linear [MutableBuffer].
  */
 class MutableBufferNDStructure<T>(
     override val strides: Strides,
@@ -246,18 +313,18 @@ class MutableBufferNDStructure<T>(
 ) : NDBuffer<T>(), MutableNDStructure<T> {
 
     init {
-        if (strides.linearSize != buffer.size) {
-            error("Expected buffer side of ${strides.linearSize}, but found ${buffer.size}")
+        require(strides.linearSize == buffer.size) {
+            "Expected buffer side of ${strides.linearSize}, but found ${buffer.size}"
         }
     }
 
-    override fun set(index: IntArray, value: T) = buffer.set(strides.offset(index), value)
+    override operator fun set(index: IntArray, value: T): Unit = buffer.set(strides.offset(index), value)
 }
 
 inline fun <reified T : Any> NDStructure<T>.combine(
     struct: NDStructure<T>,
     crossinline block: (T, T) -> T
 ): NDStructure<T> {
-    if (!this.shape.contentEquals(struct.shape)) error("Shape mismatch in structure combination")
+    require(shape.contentEquals(struct.shape)) { "Shape mismatch in structure combination" }
     return NDStructure.auto(shape) { block(this[it], struct[it]) }
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/RealBuffer.kt

@@ -1,34 +1,55 @@
 package scientifik.kmath.structures
 
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
+
+/**
+ * Specialized [MutableBuffer] implementation over [DoubleArray].
+ *
+ * @property array the underlying array.
+ */
 inline class RealBuffer(val array: DoubleArray) : MutableBuffer<Double> {
     override val size: Int get() = array.size
 
-    override fun get(index: Int): Double = array[index]
+    override operator fun get(index: Int): Double = array[index]
 
-    override fun set(index: Int, value: Double) {
+    override operator fun set(index: Int, value: Double) {
         array[index] = value
     }
 
-    override fun iterator() = array.iterator()
+    override operator fun iterator(): DoubleIterator = array.iterator()
 
     override fun copy(): MutableBuffer<Double> =
         RealBuffer(array.copyOf())
 }
 
-@Suppress("FunctionName")
-inline fun RealBuffer(size: Int, init: (Int) -> Double): RealBuffer = RealBuffer(DoubleArray(size) { init(it) })
+/**
+ * Creates a new [RealBuffer] with the specified [size], where each element is calculated by calling the specified
+ * [init] function.
+ *
+ * The function [init] is called for each array element sequentially starting from the first one.
+ * It should return the value for an buffer element given its index.
+ */
+inline fun RealBuffer(size: Int, init: (Int) -> Double): RealBuffer {
+    contract { callsInPlace(init) }
+    return RealBuffer(DoubleArray(size) { init(it) })
+}
 
-@Suppress("FunctionName")
+/**
+ * Returns a new [RealBuffer] of given elements.
+ */
 fun RealBuffer(vararg doubles: Double): RealBuffer = RealBuffer(doubles)
 
 /**
- * Transform buffer of doubles into array for high performance operations
+ * Returns a [DoubleArray] containing all of the elements of this [MutableBuffer].
  */
 val MutableBuffer<out Double>.array: DoubleArray
-    get() = if (this is RealBuffer) {
-        array
-    } else {
-        DoubleArray(size) { get(it) }
-    }
+    get() = (if (this is RealBuffer) array else DoubleArray(size) { get(it) })
 
-fun DoubleArray.asBuffer() = RealBuffer(this)
+/**
+ * Returns [RealBuffer] over this array.
+ *
+ * @receiver the array.
+ * @return the new buffer.
+ */
+fun DoubleArray.asBuffer(): RealBuffer = RealBuffer(this)

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/RealBufferField.kt

@@ -6,18 +6,19 @@ import kotlin.math.*
 
 
 /**
- * A simple field over linear buffers of [Double]
+ * [ExtendedFieldOperations] over [RealBuffer].
  */
 object RealBufferFieldOperations : ExtendedFieldOperations<Buffer<Double>> {
     override fun add(a: Buffer<Double>, b: Buffer<Double>): RealBuffer {
-        require(b.size == a.size) { "The size of the first buffer ${a.size} should be the same as for second one: ${b.size} " }
+        require(b.size == a.size) {
+            "The size of the first buffer ${a.size} should be the same as for second one: ${b.size} "
+        }
 
         return if (a is RealBuffer && b is RealBuffer) {
             val aArray = a.array
             val bArray = b.array
             RealBuffer(DoubleArray(a.size) { aArray[it] + bArray[it] })
-        } else
-            RealBuffer(DoubleArray(a.size) { a[it] + b[it] })
+        } else RealBuffer(DoubleArray(a.size) { a[it] + b[it] })
     }
 
     override fun multiply(a: Buffer<Double>, k: Number): RealBuffer {
@@ -26,12 +27,13 @@ object RealBufferFieldOperations : ExtendedFieldOperations<Buffer<Double>> {
         return if (a is RealBuffer) {
             val aArray = a.array
             RealBuffer(DoubleArray(a.size) { aArray[it] * kValue })
-        } else
-            RealBuffer(DoubleArray(a.size) { a[it] * kValue })
+        } else RealBuffer(DoubleArray(a.size) { a[it] * kValue })
     }
 
     override fun multiply(a: Buffer<Double>, b: Buffer<Double>): RealBuffer {
-        require(b.size == a.size) { "The size of the first buffer ${a.size} should be the same as for second one: ${b.size} " }
+        require(b.size == a.size) {
+            "The size of the first buffer ${a.size} should be the same as for second one: ${b.size} "
+        }
 
         return if (a is RealBuffer && b is RealBuffer) {
             val aArray = a.array
@@ -42,34 +44,31 @@ object RealBufferFieldOperations : ExtendedFieldOperations<Buffer<Double>> {
     }
 
     override fun divide(a: Buffer<Double>, b: Buffer<Double>): RealBuffer {
-        require(b.size == a.size) { "The size of the first buffer ${a.size} should be the same as for second one: ${b.size} " }
+        require(b.size == a.size) {
+            "The size of the first buffer ${a.size} should be the same as for second one: ${b.size} "
+        }
 
         return if (a is RealBuffer && b is RealBuffer) {
             val aArray = a.array
             val bArray = b.array
             RealBuffer(DoubleArray(a.size) { aArray[it] / bArray[it] })
-        } else
-            RealBuffer(DoubleArray(a.size) { a[it] / b[it] })
+        } else RealBuffer(DoubleArray(a.size) { a[it] / b[it] })
     }
 
     override fun sin(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
         val array = arg.array
         RealBuffer(DoubleArray(arg.size) { sin(array[it]) })
-    } else {
-        RealBuffer(DoubleArray(arg.size) { sin(arg[it]) })
-    }
+    } else RealBuffer(DoubleArray(arg.size) { sin(arg[it]) })
 
     override fun cos(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
         val array = arg.array
         RealBuffer(DoubleArray(arg.size) { cos(array[it]) })
-    } else
-        RealBuffer(DoubleArray(arg.size) { cos(arg[it]) })
+    } else RealBuffer(DoubleArray(arg.size) { cos(arg[it]) })
 
     override fun tan(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
         val array = arg.array
         RealBuffer(DoubleArray(arg.size) { tan(array[it]) })
-    } else
-        RealBuffer(DoubleArray(arg.size) { tan(arg[it]) })
+    } else RealBuffer(DoubleArray(arg.size) { tan(arg[it]) })
 
     override fun asin(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
         val array = arg.array
@@ -90,25 +89,57 @@ object RealBufferFieldOperations : ExtendedFieldOperations<Buffer<Double>> {
     } else
         RealBuffer(DoubleArray(arg.size) { atan(arg[it]) })
 
+    override fun sinh(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
+        val array = arg.array
+        RealBuffer(DoubleArray(arg.size) { sinh(array[it]) })
+    } else RealBuffer(DoubleArray(arg.size) { sinh(arg[it]) })
+
+    override fun cosh(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
+        val array = arg.array
+        RealBuffer(DoubleArray(arg.size) { cosh(array[it]) })
+    } else RealBuffer(DoubleArray(arg.size) { cosh(arg[it]) })
+
+    override fun tanh(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
+        val array = arg.array
+        RealBuffer(DoubleArray(arg.size) { tanh(array[it]) })
+    } else RealBuffer(DoubleArray(arg.size) { tanh(arg[it]) })
+
+    override fun asinh(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
+        val array = arg.array
+        RealBuffer(DoubleArray(arg.size) { asinh(array[it]) })
+    } else RealBuffer(DoubleArray(arg.size) { asinh(arg[it]) })
+
+    override fun acosh(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
+        val array = arg.array
+        RealBuffer(DoubleArray(arg.size) { acosh(array[it]) })
+    } else RealBuffer(DoubleArray(arg.size) { acosh(arg[it]) })
+
+    override fun atanh(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
+        val array = arg.array
+        RealBuffer(DoubleArray(arg.size) { atanh(array[it]) })
+    } else RealBuffer(DoubleArray(arg.size) { atanh(arg[it]) })
+
     override fun power(arg: Buffer<Double>, pow: Number): RealBuffer = if (arg is RealBuffer) {
         val array = arg.array
         RealBuffer(DoubleArray(arg.size) { array[it].pow(pow.toDouble()) })
-    } else
-        RealBuffer(DoubleArray(arg.size) { arg[it].pow(pow.toDouble()) })
+    } else RealBuffer(DoubleArray(arg.size) { arg[it].pow(pow.toDouble()) })
 
     override fun exp(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
         val array = arg.array
         RealBuffer(DoubleArray(arg.size) { exp(array[it]) })
-    } else
-        RealBuffer(DoubleArray(arg.size) { exp(arg[it]) })
+    } else RealBuffer(DoubleArray(arg.size) { exp(arg[it]) })
 
     override fun ln(arg: Buffer<Double>): RealBuffer = if (arg is RealBuffer) {
         val array = arg.array
         RealBuffer(DoubleArray(arg.size) { ln(array[it]) })
-    } else
-        RealBuffer(DoubleArray(arg.size) { ln(arg[it]) })
+    } else RealBuffer(DoubleArray(arg.size) { ln(arg[it]) })
 }
 
+/**
+ * [ExtendedField] over [RealBuffer].
+ *
+ * @property size the size of buffers to operate on.
+ */
 class RealBufferField(val size: Int) : ExtendedField<Buffer<Double>> {
     override val zero: Buffer<Double> by lazy { RealBuffer(size) { 0.0 } }
     override val one: Buffer<Double> by lazy { RealBuffer(size) { 1.0 } }
@@ -163,6 +194,36 @@ class RealBufferField(val size: Int) : ExtendedField<Buffer<Double>> {
         return RealBufferFieldOperations.atan(arg)
     }
 
+    override fun sinh(arg: Buffer<Double>): RealBuffer {
+        require(arg.size == size) { "The buffer size ${arg.size} does not match context size $size" }
+        return RealBufferFieldOperations.sinh(arg)
+    }
+
+    override fun cosh(arg: Buffer<Double>): RealBuffer {
+        require(arg.size == size) { "The buffer size ${arg.size} does not match context size $size" }
+        return RealBufferFieldOperations.cosh(arg)
+    }
+
+    override fun tanh(arg: Buffer<Double>): RealBuffer {
+        require(arg.size == size) { "The buffer size ${arg.size} does not match context size $size" }
+        return RealBufferFieldOperations.tanh(arg)
+    }
+
+    override fun asinh(arg: Buffer<Double>): RealBuffer {
+        require(arg.size == size) { "The buffer size ${arg.size} does not match context size $size" }
+        return RealBufferFieldOperations.asinh(arg)
+    }
+
+    override fun acosh(arg: Buffer<Double>): RealBuffer {
+        require(arg.size == size) { "The buffer size ${arg.size} does not match context size $size" }
+        return RealBufferFieldOperations.acosh(arg)
+    }
+
+    override fun atanh(arg: Buffer<Double>): RealBuffer {
+        require(arg.size == size) { "The buffer size ${arg.size} does not match context size $size" }
+        return RealBufferFieldOperations.atanh(arg)
+    }
+
     override fun power(arg: Buffer<Double>, pow: Number): RealBuffer {
         require(arg.size == size) { "The buffer size ${arg.size} does not match context size $size" }
         return RealBufferFieldOperations.power(arg, pow)

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/RealNDField.kt

@@ -12,8 +12,8 @@ class RealNDField(override val shape: IntArray) :
     override val strides: Strides = DefaultStrides(shape)
 
     override val elementContext: RealField get() = RealField
-    override val zero by lazy { produce { zero } }
-    override val one by lazy { produce { one } }
+    override val zero: RealNDElement by lazy { produce { zero } }
+    override val one: RealNDElement by lazy { produce { one } }
 
     inline fun buildBuffer(size: Int, crossinline initializer: (Int) -> Double): Buffer<Double> =
         RealBuffer(DoubleArray(size) { initializer(it) })
@@ -40,6 +40,7 @@ class RealNDField(override val shape: IntArray) :
         transform: RealField.(index: IntArray, Double) -> Double
     ): RealNDElement {
         check(arg)
+
         return BufferedNDFieldElement(
             this,
             buildBuffer(arg.strides.linearSize) { offset ->
@@ -64,23 +65,25 @@ class RealNDField(override val shape: IntArray) :
     override fun NDBuffer<Double>.toElement(): FieldElement<NDBuffer<Double>, *, out BufferedNDField<Double, RealField>> =
         BufferedNDFieldElement(this@RealNDField, buffer)
 
-    override fun power(arg: NDBuffer<Double>, pow: Number) = map(arg) { power(it, pow) }
+    override fun power(arg: NDBuffer<Double>, pow: Number): RealNDElement = map(arg) { power(it, pow) }
 
-    override fun exp(arg: NDBuffer<Double>) = map(arg) { exp(it) }
+    override fun exp(arg: NDBuffer<Double>): RealNDElement = map(arg) { exp(it) }
 
-    override fun ln(arg: NDBuffer<Double>) = map(arg) { ln(it) }
+    override fun ln(arg: NDBuffer<Double>): RealNDElement = map(arg) { ln(it) }
 
-    override fun sin(arg: NDBuffer<Double>) = map(arg) { sin(it) }
+    override fun sin(arg: NDBuffer<Double>): RealNDElement = map(arg) { sin(it) }
+    override fun cos(arg: NDBuffer<Double>): RealNDElement = map(arg) { cos(it) }
+    override fun tan(arg: NDBuffer<Double>): RealNDElement = map(arg) { tan(it) }
+    override fun asin(arg: NDBuffer<Double>): RealNDElement = map(arg) { asin(it) }
+    override fun acos(arg: NDBuffer<Double>): RealNDElement = map(arg) { acos(it) }
+    override fun atan(arg: NDBuffer<Double>): RealNDElement = map(arg) { atan(it) }
 
-    override fun cos(arg: NDBuffer<Double>) = map(arg) { cos(it) }
-
-    override fun tan(arg: NDBuffer<Double>): NDBuffer<Double> = map(arg) { tan(it) }
-
-    override fun asin(arg: NDBuffer<Double>): NDBuffer<Double> = map(arg) { asin(it) }
-
-    override fun acos(arg: NDBuffer<Double>): NDBuffer<Double> = map(arg) { acos(it) }
-
-    override fun atan(arg: NDBuffer<Double>): NDBuffer<Double> = map(arg) { atan(it) }
+    override fun sinh(arg: NDBuffer<Double>): RealNDElement = map(arg) { sinh(it) }
+    override fun cosh(arg: NDBuffer<Double>): RealNDElement = map(arg) { cosh(it) }
+    override fun tanh(arg: NDBuffer<Double>): RealNDElement = map(arg) { tanh(it) }
+    override fun asinh(arg: NDBuffer<Double>): RealNDElement = map(arg) { asinh(it) }
+    override fun acosh(arg: NDBuffer<Double>): RealNDElement = map(arg) { acosh(it) }
+    override fun atanh(arg: NDBuffer<Double>): RealNDElement = map(arg) { atanh(it) }
 }
 
 
@@ -93,13 +96,13 @@ inline fun BufferedNDField<Double, RealField>.produceInline(crossinline initiali
 }
 
 /**
- * Map one [RealNDElement] using function with indexes
+ * Map one [RealNDElement] using function with indices.
  */
-inline fun RealNDElement.mapIndexed(crossinline transform: RealField.(index: IntArray, Double) -> Double) =
+inline fun RealNDElement.mapIndexed(crossinline transform: RealField.(index: IntArray, Double) -> Double): RealNDElement =
     context.produceInline { offset -> transform(strides.index(offset), buffer[offset]) }
 
 /**
- * Map one [RealNDElement] using function without indexes
+ * Map one [RealNDElement] using function without indices.
  */
 inline fun RealNDElement.map(crossinline transform: RealField.(Double) -> Double): RealNDElement {
     val array = DoubleArray(strides.linearSize) { offset -> RealField.transform(buffer[offset]) }
@@ -107,9 +110,9 @@ inline fun RealNDElement.map(crossinline transform: RealField.(Double) -> Double
 }
 
 /**
- * Element by element application of any operation on elements to the whole array. Just like in numpy
+ * Element by element application of any operation on elements to the whole array. Just like in numpy.
  */
-operator fun Function1<Double, Double>.invoke(ndElement: RealNDElement) =
+operator fun Function1<Double, Double>.invoke(ndElement: RealNDElement): RealNDElement =
     ndElement.map { this@invoke(it) }
 
 
@@ -118,18 +121,17 @@ operator fun Function1<Double, Double>.invoke(ndElement: RealNDElement) =
 /**
  * Summation operation for [BufferedNDElement] and single element
  */
-operator fun RealNDElement.plus(arg: Double) =
+operator fun RealNDElement.plus(arg: Double): RealNDElement =
     map { it + arg }
 
 /**
  * Subtraction operation between [BufferedNDElement] and single element
  */
-operator fun RealNDElement.minus(arg: Double) =
+operator fun RealNDElement.minus(arg: Double): RealNDElement =
     map { it - arg }
 
 /**
  * Produce a context for n-dimensional operations inside this real field
  */
-inline fun <R> RealField.nd(vararg shape: Int, action: RealNDField.() -> R): R {
-    return NDField.real(*shape).run(action)
-}
+
+inline fun <R> RealField.nd(vararg shape: Int, action: RealNDField.() -> R): R = NDField.real(*shape).run(action)

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/ShortBuffer.kt

@@ -1,20 +1,55 @@
 package scientifik.kmath.structures
 
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
+
+/**
+ * Specialized [MutableBuffer] implementation over [ShortArray].
+ *
+ * @property array the underlying array.
+ */
 inline class ShortBuffer(val array: ShortArray) : MutableBuffer<Short> {
     override val size: Int get() = array.size
 
-    override fun get(index: Int): Short = array[index]
+    override operator fun get(index: Int): Short = array[index]
 
-    override fun set(index: Int, value: Short) {
+    override operator fun set(index: Int, value: Short) {
         array[index] = value
     }
 
-    override fun iterator() = array.iterator()
+    override operator fun iterator(): ShortIterator = array.iterator()
 
     override fun copy(): MutableBuffer<Short> =
         ShortBuffer(array.copyOf())
-
 }
 
+/**
+ * Creates a new [ShortBuffer] with the specified [size], where each element is calculated by calling the specified
+ * [init] function.
+ *
+ * The function [init] is called for each array element sequentially starting from the first one.
+ * It should return the value for an buffer element given its index.
+ */
+inline fun ShortBuffer(size: Int, init: (Int) -> Short): ShortBuffer {
+    contract { callsInPlace(init) }
+    return ShortBuffer(ShortArray(size) { init(it) })
+}
 
-fun ShortArray.asBuffer() = ShortBuffer(this)
+/**
+ * Returns a new [ShortBuffer] of given elements.
+ */
+fun ShortBuffer(vararg shorts: Short): ShortBuffer = ShortBuffer(shorts)
+
+/**
+ * Returns a [ShortArray] containing all of the elements of this [MutableBuffer].
+ */
+val MutableBuffer<out Short>.array: ShortArray
+    get() = (if (this is ShortBuffer) array else ShortArray(size) { get(it) })
+
+/**
+ * Returns [ShortBuffer] over this array.
+ *
+ * @receiver the array.
+ * @return the new buffer.
+ */
+fun ShortArray.asBuffer(): ShortBuffer = ShortBuffer(this)

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/ShortNDRing.kt

@@ -12,8 +12,8 @@ class ShortNDRing(override val shape: IntArray) :
     override val strides: Strides = DefaultStrides(shape)
 
     override val elementContext: ShortRing get() = ShortRing
-    override val zero by lazy { produce { ShortRing.zero } }
-    override val one by lazy { produce { ShortRing.one } }
+    override val zero: ShortNDElement by lazy { produce { zero } }
+    override val one: ShortNDElement by lazy { produce { one } }
 
     inline fun buildBuffer(size: Int, crossinline initializer: (Int) -> Short): Buffer<Short> =
         ShortBuffer(ShortArray(size) { initializer(it) })
@@ -40,6 +40,7 @@ class ShortNDRing(override val shape: IntArray) :
         transform: ShortRing.(index: IntArray, Short) -> Short
     ): ShortNDElement {
         check(arg)
+
         return BufferedNDRingElement(
             this,
             buildBuffer(arg.strides.linearSize) { offset ->
@@ -67,7 +68,7 @@ class ShortNDRing(override val shape: IntArray) :
 
 
 /**
- * Fast element production using function inlining
+ * Fast element production using function inlining.
  */
 inline fun BufferedNDRing<Short, ShortRing>.produceInline(crossinline initializer: ShortRing.(Int) -> Short): ShortNDElement {
     val array = ShortArray(strides.linearSize) { offset -> ShortRing.initializer(offset) }
@@ -75,22 +76,22 @@ inline fun BufferedNDRing<Short, ShortRing>.produceInline(crossinline initialize
 }
 
 /**
- * Element by element application of any operation on elements to the whole array. Just like in numpy
+ * Element by element application of any operation on elements to the whole array.
  */
-operator fun Function1<Short, Short>.invoke(ndElement: ShortNDElement) =
+operator fun Function1<Short, Short>.invoke(ndElement: ShortNDElement): ShortNDElement =
     ndElement.context.produceInline { i -> invoke(ndElement.buffer[i]) }
 
 
 /* plus and minus */
 
 /**
- * Summation operation for [StridedNDFieldElement] and single element
+ * Summation operation for [ShortNDElement] and single element.
  */
-operator fun ShortNDElement.plus(arg: Short) =
+operator fun ShortNDElement.plus(arg: Short): ShortNDElement =
     context.produceInline { i -> (buffer[i] + arg).toShort() }
 
 /**
- * Subtraction operation between [StridedNDFieldElement] and single element
+ * Subtraction operation between [ShortNDElement] and single element.
  */
-operator fun ShortNDElement.minus(arg: Short) =
+operator fun ShortNDElement.minus(arg: Short): ShortNDElement =
     context.produceInline { i -> (buffer[i] - arg).toShort() }

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/Structure1D.kt

@@ -6,23 +6,23 @@ package scientifik.kmath.structures
 interface Structure1D<T> : NDStructure<T>, Buffer<T> {
     override val dimension: Int get() = 1
 
-    override fun get(index: IntArray): T {
-        if (index.size != 1) error("Index dimension mismatch. Expected 1 but found ${index.size}")
+    override operator fun get(index: IntArray): T {
+        require(index.size == 1) { "Index dimension mismatch. Expected 1 but found ${index.size}" }
         return get(index[0])
     }
 
-    override fun iterator(): Iterator<T> = (0 until size).asSequence().map { get(it) }.iterator()
+    override operator fun iterator(): Iterator<T> = (0 until size).asSequence().map { get(it) }.iterator()
 }
 
 /**
  * A 1D wrapper for nd-structure
  */
-private inline class Structure1DWrapper<T>(val structure: NDStructure<T>) : Structure1D<T>{
+private inline class Structure1DWrapper<T>(val structure: NDStructure<T>) : Structure1D<T> {
 
     override val shape: IntArray get() = structure.shape
     override val size: Int get() = structure.shape[0]
 
-    override fun get(index: Int): T = structure[index]
+    override operator fun get(index: Int): T = structure[index]
 
     override fun elements(): Sequence<Pair<IntArray, T>> = structure.elements()
 }
@@ -39,14 +39,14 @@ private inline class Buffer1DWrapper<T>(val buffer: Buffer<T>) : Structure1D<T>
     override fun elements(): Sequence<Pair<IntArray, T>> =
         asSequence().mapIndexed { index, value -> intArrayOf(index) to value }
 
-    override fun get(index: Int): T = buffer.get(index)
+    override operator fun get(index: Int): T = buffer[index]
 }
 
 /**
  * Represent a [NDStructure] as [Structure1D]. Throw error in case of dimension mismatch
  */
 fun <T> NDStructure<T>.as1D(): Structure1D<T> = if (shape.size == 1) {
-    if( this is NDBuffer){
+    if (this is NDBuffer) {
         Buffer1DWrapper(this.buffer)
     } else {
         Structure1DWrapper(this)

kmath-core/src/commonMain/kotlin/scientifik/kmath/structures/Structure2D.kt

@@ -9,8 +9,8 @@ interface Structure2D<T> : NDStructure<T> {
 
     operator fun get(i: Int, j: Int): T
 
-    override fun get(index: IntArray): T {
-        if (index.size != 2) error("Index dimension mismatch. Expected 2 but found ${index.size}")
+    override operator fun get(index: IntArray): T {
+        require(index.size == 2) { "Index dimension mismatch. Expected 2 but found ${index.size}" }
         return get(index[0], index[1])
     }
 
@@ -32,19 +32,17 @@ interface Structure2D<T> : NDStructure<T> {
         }
     }
 
-    companion object {
-
-    }
+    companion object
 }
 
 /**
  * A 2D wrapper for nd-structure
  */
 private inline class Structure2DWrapper<T>(val structure: NDStructure<T>) : Structure2D<T> {
-    override fun get(i: Int, j: Int): T = structure[i, j]
-
     override val shape: IntArray get() = structure.shape
 
+    override operator fun get(i: Int, j: Int): T = structure[i, j]
+
     override fun elements(): Sequence<Pair<IntArray, T>> = structure.elements()
 }
 

kmath-core/src/commonTest/kotlin/scientifik/kmath/expressions/ExpressionFieldTest.kt

@@ -3,6 +3,7 @@ package scientifik.kmath.expressions
 import scientifik.kmath.operations.Complex
 import scientifik.kmath.operations.ComplexField
 import scientifik.kmath.operations.RealField
+import scientifik.kmath.operations.invoke
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
@@ -10,10 +11,12 @@ class ExpressionFieldTest {
     @Test
     fun testExpression() {
         val context = FunctionalExpressionField(RealField)
-        val expression = with(context) {
+
+        val expression = context {
             val x = variable("x", 2.0)
             x * x + 2 * x + one
         }
+
         assertEquals(expression("x" to 1.0), 4.0)
         assertEquals(expression(), 9.0)
     }
@@ -21,17 +24,19 @@ class ExpressionFieldTest {
     @Test
     fun testComplex() {
         val context = FunctionalExpressionField(ComplexField)
-        val expression = with(context) {
+
+        val expression = context {
             val x = variable("x", Complex(2.0, 0.0))
             x * x + 2 * x + one
         }
+
         assertEquals(expression("x" to Complex(1.0, 0.0)), Complex(4.0, 0.0))
         assertEquals(expression(), Complex(9.0, 0.0))
     }
 
     @Test
     fun separateContext() {
-        fun <T> FunctionalExpressionField<T,*>.expression(): Expression<T> {
+        fun <T> FunctionalExpressionField<T, *>.expression(): Expression<T> {
             val x = variable("x")
             return x * x + 2 * x + one
         }
@@ -42,7 +47,7 @@ class ExpressionFieldTest {
 
     @Test
     fun valueExpression() {
-        val expressionBuilder: FunctionalExpressionField<Double,*>.() -> Expression<Double> = {
+        val expressionBuilder: FunctionalExpressionField<Double, *>.() -> Expression<Double> = {
             val x = variable("x")
             x * x + 2 * x + one
         }

kmath-core/src/commonTest/kotlin/scientifik/kmath/linear/MatrixTest.kt

@@ -7,7 +7,6 @@ import kotlin.test.Test
 import kotlin.test.assertEquals
 
 class MatrixTest {
-
     @Test
     fun testTranspose() {
         val matrix = MatrixContext.real.one(3, 3)
@@ -49,17 +48,18 @@ class MatrixTest {
 
     @Test
     fun test2DDot() {
-        val firstMatrix = NDStructure.auto(2,3){ (i, j) -> (i + j).toDouble() }.as2D()
-        val secondMatrix = NDStructure.auto(3,2){ (i, j) -> (i + j).toDouble() }.as2D()
+        val firstMatrix = NDStructure.auto(2, 3) { (i, j) -> (i + j).toDouble() }.as2D()
+        val secondMatrix = NDStructure.auto(3, 2) { (i, j) -> (i + j).toDouble() }.as2D()
+
         MatrixContext.real.run {
 //            val firstMatrix = produce(2, 3) { i, j -> (i + j).toDouble() }
 //            val secondMatrix = produce(3, 2) { i, j -> (i + j).toDouble() }
             val result = firstMatrix dot secondMatrix
             assertEquals(2, result.rowNum)
             assertEquals(2, result.colNum)
-            assertEquals(8.0, result[0,1])
-            assertEquals(8.0, result[1,0])
-            assertEquals(14.0, result[1,1])
+            assertEquals(8.0, result[0, 1])
+            assertEquals(8.0, result[1, 0])
+            assertEquals(14.0, result[1, 1])
         }
     }
 }

kmath-core/src/commonTest/kotlin/scientifik/kmath/misc/AutoDiffTest.kt

@@ -8,10 +8,10 @@ import kotlin.test.assertEquals
 import kotlin.test.assertTrue
 
 class AutoDiffTest {
+    fun Variable(int: Int): Variable<Double> = Variable(int.toDouble())
 
-    fun Variable(int: Int) = Variable(int.toDouble())
-
-    fun deriv(body: AutoDiffField<Double, RealField>.() -> Variable<Double>) = RealField.deriv(body)
+    fun deriv(body: AutoDiffField<Double, RealField>.() -> Variable<Double>): DerivationResult<Double> =
+        RealField.deriv(body)
 
     @Test
     fun testPlusX2() {
@@ -178,5 +178,4 @@ class AutoDiffTest {
     private fun assertApprox(a: Double, b: Double) {
         if ((a - b) > 1e-10) assertEquals(a, b)
     }
-
 }

kmath-core/src/commonTest/kotlin/scientifik/kmath/operations/BigIntAlgebraTest.kt

@@ -1,9 +1,13 @@
 package scientifik.kmath.operations
 
+import scientifik.kmath.operations.internal.RingVerifier
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
-class BigIntAlgebraTest {
+internal class BigIntAlgebraTest {
+    @Test
+    fun verify() = BigIntField { RingVerifier(this, +"42", +"10", +"-12", 10).verify() }
+
     @Test
     fun testKBigIntegerRingSum() {
         val res = BigIntField {
@@ -47,4 +51,3 @@ class BigIntAlgebraTest {
     }
 
 }
-

kmath-core/src/commonTest/kotlin/scientifik/kmath/operations/BigIntConstructorTest.kt

@@ -19,7 +19,7 @@ class BigIntConstructorTest {
 
     @Test
     fun testConstructor_0xffffffffaL() {
-        val x = -0xffffffffaL.toBigInt()
+        val x = (-0xffffffffaL).toBigInt()
         val y = uintArrayOf(0xfffffffaU, 0xfU).toBigInt(-1)
         assertEquals(x, y)
     }

kmath-core/src/commonTest/kotlin/scientifik/kmath/operations/BigIntConversionsTest.kt

@@ -19,7 +19,7 @@ class BigIntConversionsTest {
 
     @Test
     fun testToString_0x17ead2ffffd() {
-        val x = -0x17ead2ffffdL.toBigInt()
+        val x = (-0x17ead2ffffdL).toBigInt()
         assertEquals("-0x17ead2ffffd", x.toString())
     }
 

kmath-core/src/commonTest/kotlin/scientifik/kmath/operations/BigIntOperationsTest.kt

@@ -31,7 +31,7 @@ class BigIntOperationsTest {
     @Test
     fun testUnaryMinus() {
         val x = 1234.toBigInt()
-        val y = -1234.toBigInt()
+        val y = (-1234).toBigInt()
         assertEquals(-x, y)
     }
 
@@ -48,18 +48,18 @@ class BigIntOperationsTest {
 
     @Test
     fun testMinus__2_1() {
-        val x = -2.toBigInt()
+        val x = (-2).toBigInt()
         val y = 1.toBigInt()
 
         val res = x - y
-        val sum = -3.toBigInt()
+        val sum = (-3).toBigInt()
 
         assertEquals(sum, res)
     }
 
     @Test
     fun testMinus___2_1() {
-        val x = -2.toBigInt()
+        val x = (-2).toBigInt()
         val y = 1.toBigInt()
 
         val res = -x - y
@@ -74,7 +74,7 @@ class BigIntOperationsTest {
         val y = 0xffffffffaL.toBigInt()
 
         val res = x - y
-        val sum = -0xfffffcfc1L.toBigInt()
+        val sum = (-0xfffffcfc1L).toBigInt()
 
         assertEquals(sum, res)
     }
@@ -92,11 +92,11 @@ class BigIntOperationsTest {
 
     @Test
     fun testMultiply__2_3() {
-        val x = -2.toBigInt()
+        val x = (-2).toBigInt()
         val y = 3.toBigInt()
 
         val res = x * y
-        val prod = -6.toBigInt()
+        val prod = (-6).toBigInt()
 
         assertEquals(prod, res)
     }
@@ -129,7 +129,7 @@ class BigIntOperationsTest {
         val y = -0xfff456
 
         val res = x * y
-        val prod = -0xffe579ad5dc2L.toBigInt()
+        val prod = (-0xffe579ad5dc2L).toBigInt()
 
         assertEquals(prod, res)
     }
@@ -259,7 +259,7 @@ class BigIntOperationsTest {
         val y = -3
 
         val res = x / y
-        val div = -6.toBigInt()
+        val div = (-6).toBigInt()
 
         assertEquals(div, res)
     }
@@ -267,10 +267,10 @@ class BigIntOperationsTest {
     @Test
     fun testBigDivision_20__3() {
         val x = 20.toBigInt()
-        val y = -3.toBigInt()
+        val y = (-3).toBigInt()
 
         val res = x / y
-        val div = -6.toBigInt()
+        val div = (-6).toBigInt()
 
         assertEquals(div, res)
     }

kmath-core/src/commonTest/kotlin/scientifik/kmath/operations/ComplexFieldTest.kt

@@ -0,0 +1,77 @@
+package scientifik.kmath.operations
+
+import scientifik.kmath.operations.internal.FieldVerifier
+import kotlin.math.PI
+import kotlin.math.abs
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+internal class ComplexFieldTest {
+    @Test
+    fun verify() = ComplexField { FieldVerifier(this, 42.0 * i, 66.0 + 28 * i, 2.0 + 0 * i, 5).verify() }
+
+    @Test
+    fun testAddition() {
+        assertEquals(Complex(42, 42), ComplexField { Complex(16, 16) + Complex(26, 26) })
+        assertEquals(Complex(42, 16), ComplexField { Complex(16, 16) + 26 })
+        assertEquals(Complex(42, 16), ComplexField { 26 + Complex(16, 16) })
+    }
+
+    @Test
+    fun testSubtraction() {
+        assertEquals(Complex(42, 42), ComplexField { Complex(86, 55) - Complex(44, 13) })
+        assertEquals(Complex(42, 56), ComplexField { Complex(86, 56) - 44 })
+        assertEquals(Complex(42, 56), ComplexField { 86 - Complex(44, -56) })
+    }
+
+    @Test
+    fun testMultiplication() {
+        assertEquals(Complex(42, 42), ComplexField { Complex(4.2, 0) * Complex(10, 10) })
+        assertEquals(Complex(42, 21), ComplexField { Complex(4.2, 2.1) * 10 })
+        assertEquals(Complex(42, 21), ComplexField { 10 * Complex(4.2, 2.1) })
+    }
+
+    @Test
+    fun testDivision() {
+        assertEquals(Complex(42, 42), ComplexField { Complex(0, 168) / Complex(2, 2) })
+        assertEquals(Complex(42, 56), ComplexField { Complex(86, 56) - 44 })
+        assertEquals(Complex(42, 56), ComplexField { 86 - Complex(44, -56) })
+        assertEquals(Complex(Double.NaN, Double.NaN), ComplexField { Complex(1, 1) / Complex(Double.NaN, Double.NaN) })
+        assertEquals(Complex(Double.NaN, Double.NaN), ComplexField { Complex(1, 1) / Complex(0, 0) })
+    }
+
+    @Test
+    fun testSine() {
+        assertEquals(ComplexField { i * sinh(one) }, ComplexField { sin(i) })
+        assertEquals(ComplexField { i * sinh(PI.toComplex()) }, ComplexField { sin(i * PI.toComplex()) })
+    }
+
+    @Test
+    fun testInverseSine() {
+        assertEquals(Complex(0, -0.0), ComplexField { asin(zero) })
+        assertTrue(abs(ComplexField { i * asinh(one) }.r - ComplexField { asin(i) }.r) < 0.000000000000001)
+    }
+
+    @Test
+    fun testInverseHyperbolicSine() {
+        assertEquals(
+            ComplexField { i * PI.toComplex() / 2 },
+            ComplexField { asinh(i) })
+    }
+
+    @Test
+    fun testPower() {
+        assertEquals(ComplexField.zero, ComplexField { zero pow 2 })
+        assertEquals(ComplexField.zero, ComplexField { zero pow 2 })
+
+        assertEquals(
+            ComplexField { i * 8 }.let { it.im.toInt() to it.re.toInt() },
+            ComplexField { Complex(2, 2) pow 2 }.let { it.im.toInt() to it.re.toInt() })
+    }
+
+    @Test
+    fun testNorm() {
+        assertEquals(2.toComplex(), ComplexField { norm(2 * i) })
+    }
+}

kmath-core/src/commonTest/kotlin/scientifik/kmath/operations/ComplexTest.kt

@@ -0,0 +1,38 @@
+package scientifik.kmath.operations
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+internal class ComplexTest {
+    @Test
+    fun conjugate() {
+        assertEquals(
+            Complex(0, -42), (ComplexField.i * 42).conjugate
+        )
+    }
+
+    @Test
+    fun reciprocal() {
+        assertEquals(Complex(0.5, -0.0), 2.toComplex().reciprocal)
+    }
+
+    @Test
+    fun r() {
+        assertEquals(kotlin.math.sqrt(2.0), (ComplexField.i + 1.0.toComplex()).r)
+    }
+
+    @Test
+    fun theta() {
+        assertEquals(0.0, 1.toComplex().theta)
+    }
+
+    @Test
+    fun toComplex() {
+        assertEquals(Complex(42, 0), 42.toComplex())
+        assertEquals(Complex(42.0, 0), 42.0.toComplex())
+        assertEquals(Complex(42f, 0), 42f.toComplex())
+        assertEquals(Complex(42.0, 0), 42.0.toComplex())
+        assertEquals(Complex(42.toByte(), 0), 42.toByte().toComplex())
+        assertEquals(Complex(42.toShort(), 0), 42.toShort().toComplex())
+    }
+}

kmath-core/src/commonTest/kotlin/scientifik/kmath/operations/RealFieldTest.kt

@@ -1,14 +1,16 @@
 package scientifik.kmath.operations
 
+import scientifik.kmath.operations.internal.FieldVerifier
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
-class RealFieldTest {
+internal class RealFieldTest {
+    @Test
+    fun verify() = FieldVerifier(RealField, 42.0, 66.0, 2.0, 5).verify()
+
     @Test
     fun testSqrt() {
-        val sqrt = RealField {
-            sqrt(25 * one)
-        }
+        val sqrt = RealField { sqrt(25 * one) }
         assertEquals(5.0, sqrt)
     }
 }

kmath-core/src/commonTest/kotlin/scientifik/kmath/operations/internal/AlgebraicVerifier.kt

@@ -0,0 +1,9 @@
+package scientifik.kmath.operations.internal
+
+import scientifik.kmath.operations.Algebra
+
+internal interface AlgebraicVerifier<T, out A> where A : Algebra<T> {
+    val algebra: A
+
+    fun verify()
+}