Added matrix builder for small matrices

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

@@ -107,26 +107,6 @@ interface GenericMatrixContext<T : Any, R : Ring<T>> : MatrixContext<T> {
         produce(rowNum, colNum) { i, j -> elementContext.run { get(i, j) * value } }
 }
 
-/**
- * A marker interface representing some matrix feature like diagonal, sparce, zero, etc. Features used to optimize matrix
- * operations performance in some cases.
- */
-interface MatrixFeature
-
-object DiagonalFeature : MatrixFeature
-
-object ZeroFeature : MatrixFeature
-
-object UnitFeature : MatrixFeature
-
-interface InverseMatrixFeature<T : Any> : MatrixFeature {
-    val inverse: Matrix<T>
-}
-
-interface DeterminantFeature<T : Any> : MatrixFeature {
-    val determinant: T
-}
-
 /**
  * Specialized 2-d structure
  */
@@ -173,6 +153,16 @@ interface Matrix<T : Any> : NDStructure<T> {
             val buffer = elements.asBuffer()
             return BufferMatrix(size, size, buffer)
         }
+
+        fun <T : Any> build(rows: Int, columns: Int): MatrixBuilder<T> = MatrixBuilder(rows, columns)
+    }
+}
+
+class MatrixBuilder<T : Any>(val rows: Int, val columns: Int) {
+    operator fun invoke(vararg elements: T): Matrix<T> {
+        if (rows * columns != elements.size) error("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/MatrixFeatures.kt

@@ -0,0 +1,30 @@
+package scientifik.kmath.linear
+
+/**
+ * A marker interface representing some matrix feature like diagonal, sparce, zero, etc. Features used to optimize matrix
+ * operations performance in some cases.
+ */
+interface MatrixFeature
+
+/**
+ * The matrix with this feature is considered to have only diagonal non-null elements
+ */
+object DiagonalFeature : MatrixFeature
+
+/**
+ * Matix with this feature has all zero elements
+ */
+object ZeroFeature : MatrixFeature
+
+/**
+ * Matrix with this feature have unit elements on diagonal and zero elements in all other places
+ */
+object UnitFeature : MatrixFeature
+
+interface InverseMatrixFeature<T : Any> : MatrixFeature {
+    val inverse: Matrix<T>
+}
+
+interface DeterminantFeature<T : Any> : MatrixFeature {
+    val determinant: T
+}

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

@@ -41,4 +41,14 @@ class MatrixTest {
         assertEquals(5.0, product[1, 0])
         assertEquals(6.0, product[2, 2])
     }
+
+    @Test
+    fun testBuilder() {
+        val matrix = Matrix.build<Double>(2, 3)(
+            1.0, 0.0, 0.0,
+            0.0, 1.0, 2.0
+        )
+
+        assertEquals(2.0, matrix[1, 2])
+    }
 }

kmath-koma/build.gradle.kts

@@ -8,8 +8,12 @@ repositories {
 
 kotlin {
     jvm {
-        compilations["main"].kotlinOptions.jvmTarget = "1.8"
+        compilations.all {
-        compilations["test"].kotlinOptions.jvmTarget = "1.8"
+            kotlinOptions {
+                jvmTarget = "1.8"
+                freeCompilerArgs += "-progressive"
+            }
+        }
     }
     js()