Factorized distributions/named priors

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

@@ -1,10 +1,21 @@
 package scientifik.kmath.operations
 
 import scientifik.kmath.structures.NDElement
+import scientifik.kmath.structures.NDField
 import scientifik.kmath.structures.complex
 
 fun main() {
     val element = NDElement.complex(2, 2) { index: IntArray ->
         Complex(index[0].toDouble() - index[1].toDouble(), index[0].toDouble() + index[1].toDouble())
     }
+
+
+    val compute = NDField.complex(8).run {
+        val a = produce { (it) -> i * it - it.toDouble() }
+        val b = 3
+        val c = Complex(1.0, 1.0)
+
+        (a pow b) + c
+    }
+
 }

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

@@ -56,6 +56,8 @@ object ComplexField : ExtendedFieldOperations<Complex>, Field<Complex> {
  * Complex number class
  */
 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 fun unwrap(): Complex = this
 
     override fun Complex.wrap(): Complex = this

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

@@ -32,6 +32,8 @@ fun <T : MathElement<out TrigonometricOperations<T>>> ctg(arg: T): T = arg.conte
 interface PowerOperations<T> {
     fun power(arg: T, pow: Number): T
     fun sqrt(arg: T) = power(arg, 0.5)
+
+    infix fun T.pow(pow: Number) = power(this, pow)
 }
 
 infix fun <T : MathElement<out PowerOperations<T>>> T.pow(power: Double): T = context.power(this, power)

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/Distribution.kt

@@ -20,7 +20,7 @@ interface Distribution<T : Any> : Sampler<T> {
 
     /**
      * Create a chain of samples from this distribution.
-     * The chain is not guaranteed to be stateless.
+     * The chain is not guaranteed to be stateless, but different sample chains should be independent.
      */
     override fun sample(generator: RandomGenerator): Chain<T>
 
@@ -32,7 +32,7 @@ interface Distribution<T : Any> : Sampler<T> {
 
 interface UnivariateDistribution<T : Comparable<T>> : Distribution<T> {
     /**
-     * Cumulative distribution for ordered parameter
+     * Cumulative distribution for ordered parameter (CDF)
      */
     fun cumulative(arg: T): Double
 }

kmath-prob/src/commonMain/kotlin/scientifik/kmath/prob/FactorizedDistribution.kt

@@ -0,0 +1,26 @@
+package scientifik.kmath.prob
+
+import scientifik.kmath.chains.Chain
+import scientifik.kmath.chains.SimpleChain
+
+/**
+ * A multivariate distribution which takes a map of parameters
+ */
+interface NamedDistribution<T> : Distribution<Map<String, T>>
+
+/**
+ * A multivariate distribution that has independent distributions for separate axis
+ */
+class FactorizedDistribution<T>(val distributions: Collection<NamedDistribution<T>>) : NamedDistribution<T> {
+
+    override fun probability(arg: Map<String, T>): Double {
+        return distributions.fold(1.0) { acc, distr -> acc * distr.probability(arg) }
+    }
+
+    override fun sample(generator: RandomGenerator): Chain<Map<String, T>> {
+        val chains = distributions.map { it.sample(generator) }
+        return SimpleChain<Map<String, T>> {
+            chains.fold(emptyMap()) { acc, chain -> acc + chain.next() }
+        }
+    }
+}