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

@@ -85,7 +85,7 @@ class TransposedFeature<T : Any>(val original: Matrix<T>) : MatrixFeature
 /**
  * Create a virtual transposed matrix without copying anything. `A.transpose().transpose() === A`
  */
-fun <T : Any, R : Ring<T>> Matrix<T>.transpose(): Matrix<T> {
+fun <T : Any> Matrix<T>.transpose(): Matrix<T> {
     return this.getFeature<TransposedFeature<T>>()?.original ?: VirtualMatrix(
         this.colNum,
         this.rowNum,

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

@@ -73,7 +73,8 @@ abstract class AutoDiffField : Field<Variable> {
     abstract fun <R> derive(value: R, block: (R) -> Unit): R
 
     /**
-     * A variable accessing inner state of derivatives. Use only in extensions
+     * A variable accessing inner state of derivatives.
+     * Use this function in inner builders to avoid creating additional derivative bindings
      */
     abstract var Variable.d: Double
 
@@ -111,16 +112,17 @@ private class AutoDiffContext : AutoDiffField() {
     /**
      * A variable coupled with its derivative. For internal use only
      */
-    class VariableWithDeriv(x: Double, var d: Double = 0.0): Variable(x)
+    class VariableWithDeriv(x: Double, var d: Double = 0.0) : Variable(x)
 
-    override fun variable(value: Double): Variable  = VariableWithDeriv(value)
+
+    override fun variable(value: Double): Variable = VariableWithDeriv(value)
 
     override var Variable.d: Double
         get() = (this as? VariableWithDeriv)?.d ?: derivatives[this] ?: 0.0
         set(value) {
-            if(this is VariableWithDeriv){
+            if (this is VariableWithDeriv) {
                 d = value
-            }else {
+            } else {
                 derivatives[this] = value
             }
         }

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

@@ -52,4 +52,26 @@ class MatrixTest {
 
         assertEquals(2.0, matrix[1, 2])
     }
+
+    @Test
+    fun testMatrixExtension() {
+        val transitionMatrix: Matrix<Double> = VirtualMatrix(6, 6) { row, col ->
+            when {
+                col == 0 -> .50
+                row + 1 == col -> .50
+                row == 5 && col == 5 -> 1.0
+                else -> 0.0
+            }
+        }
+
+        infix fun Matrix<Double>.pow(power: Int): Matrix<Double> {
+            var res = this
+            repeat(power - 1) {
+                res = res dot this
+            }
+            return res
+        }
+
+        val toTenthPower = transitionMatrix pow 10
+    }
 }