From 2c001cb1b32f25dc4c245bc32b4046bf78e85cca Mon Sep 17 00:00:00 2001
From: Andrei Kislitsyn <kisandy@yandex.ru>
Date: Mon, 26 Apr 2021 17:07:49 +0300
Subject: [PATCH] fix div + simple tests

---
 .../tensors/core/algebras/DoubleTensorAlgebra.kt   |  9 +++++++--
 .../kmath/tensors/core/TestDoubleTensorAlgebra.kt  | 14 ++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/kmath-tensors/src/commonMain/kotlin/space/kscience/kmath/tensors/core/algebras/DoubleTensorAlgebra.kt b/kmath-tensors/src/commonMain/kotlin/space/kscience/kmath/tensors/core/algebras/DoubleTensorAlgebra.kt
index b61a484d0..7414a4469 100644
--- a/kmath-tensors/src/commonMain/kotlin/space/kscience/kmath/tensors/core/algebras/DoubleTensorAlgebra.kt
+++ b/kmath-tensors/src/commonMain/kotlin/space/kscience/kmath/tensors/core/algebras/DoubleTensorAlgebra.kt
@@ -180,12 +180,17 @@ public open class DoubleTensorAlgebra : TensorPartialDivisionAlgebra<Double> {
 
     override fun Double.div(other: TensorStructure<Double>): DoubleTensor {
         val resBuffer = DoubleArray(other.tensor.numElements) { i ->
-            other.tensor.buffer.array()[other.tensor.bufferStart + i] / this
+            this / other.tensor.buffer.array()[other.tensor.bufferStart + i]
         }
         return DoubleTensor(other.shape, resBuffer)
     }
 
-    override fun TensorStructure<Double>.div(value: Double): DoubleTensor = value / tensor
+    override fun TensorStructure<Double>.div(value: Double): DoubleTensor {
+        val resBuffer = DoubleArray(tensor.numElements) { i ->
+            tensor.buffer.array()[tensor.bufferStart + i] / value
+        }
+        return DoubleTensor(shape, resBuffer)
+    }
 
     override fun TensorStructure<Double>.div(other: TensorStructure<Double>): DoubleTensor {
         checkShapesCompatible(tensor, other)
diff --git a/kmath-tensors/src/commonTest/kotlin/space/kscience/kmath/tensors/core/TestDoubleTensorAlgebra.kt b/kmath-tensors/src/commonTest/kotlin/space/kscience/kmath/tensors/core/TestDoubleTensorAlgebra.kt
index 10a9176dc..1333a7a1f 100644
--- a/kmath-tensors/src/commonTest/kotlin/space/kscience/kmath/tensors/core/TestDoubleTensorAlgebra.kt
+++ b/kmath-tensors/src/commonTest/kotlin/space/kscience/kmath/tensors/core/TestDoubleTensorAlgebra.kt
@@ -15,6 +15,20 @@ class TestDoubleTensorAlgebra {
         assertTrue(res.buffer.array() contentEquals doubleArrayOf(11.0, 12.0))
     }
 
+    @Test
+    fun doubleDiv() = DoubleTensorAlgebra {
+        val tensor = fromArray(intArrayOf(2), doubleArrayOf(2.0, 4.0))
+        val res = 2.0/tensor
+        assertTrue(res.buffer.array() contentEquals doubleArrayOf(1.0, 0.5))
+    }
+
+    @Test
+    fun divDouble() = DoubleTensorAlgebra {
+        val tensor = fromArray(intArrayOf(2), doubleArrayOf(10.0, 5.0))
+        val res = tensor / 2.5
+        assertTrue(res.buffer.array() contentEquals doubleArrayOf(4.0, 2.0))
+    }
+
     @Test
     fun transpose1x1() = DoubleTensorAlgebra {
         val tensor = fromArray(intArrayOf(1), doubleArrayOf(0.0))