kmath-core/src/commonMain/kotlin/space/kscience/kmath/tensors/core/DoubleLinearOpsTensorAlgebra.kt

@@ -10,9 +10,9 @@ public class DoubleLinearOpsTensorAlgebra :
     LinearOpsTensorAlgebra<Double, DoubleTensor, IntTensor>,
     DoubleTensorAlgebra() {
 
-    override fun DoubleTensor.inv(): DoubleTensor {
-        TODO("ANDREI")
-    }
+    override fun DoubleTensor.inv(): DoubleTensor = invLU()
+
+    override fun DoubleTensor.det(): DoubleTensor = detLU()
 
     override fun DoubleTensor.lu(): Pair<DoubleTensor, IntTensor> {
 
@@ -156,15 +156,11 @@ public class DoubleLinearOpsTensorAlgebra :
     private fun luMatrixDet(lu: Structure2D<Double>, pivots: Structure1D<Int>): Double {
         val m = lu.shape[0]
         val sign = if((pivots[m] - m) % 2 == 0) 1.0 else -1.0
-        var det = sign
-        for (i in 0 until m){
-            det *= lu[i, i]
-        }
-        return det
+        return (0 until m).asSequence().map { lu[it, it] }.fold(sign) { left, right -> left * right }
     }
 
     public fun DoubleTensor.detLU(): DoubleTensor {
-        val (luTensor, pivotsTensor) = this.lu()
+        val (luTensor, pivotsTensor) = lu()
         val n = shape.size
 
         val detTensorShape = IntArray(n - 1) { i -> shape[i] }
@@ -211,14 +207,12 @@ public class DoubleLinearOpsTensorAlgebra :
     }
 
     public fun DoubleTensor.invLU(): DoubleTensor {
-        val (luTensor, pivotsTensor) = this.lu()
+        val (luTensor, pivotsTensor) = lu()
         val n = shape.size
         val invTensor = luTensor.zeroesLike()
 
-        for (
-        (luP, invMatrix) in
-        luTensor.matrixSequence().zip(pivotsTensor.vectorSequence()).zip(invTensor.matrixSequence())
-        ) {
+        val seq = luTensor.matrixSequence().zip(pivotsTensor.vectorSequence()).zip(invTensor.matrixSequence())
+        for ((luP, invMatrix) in seq) {
             val (lu, pivots) = luP
             luMatrixInv(lu, pivots, invMatrix)
         }