examples/src/main/kotlin/space/kscience/kmath/tensors/neuralNetwork.kt

@@ -163,7 +163,7 @@ class NeuralNetwork(private val layers: List<Layer>) {
             for ((xBatch, yBatch) in iterBatch(xTrain, yTrain)) {
                 train(xBatch, yBatch)
             }
-            println("Accuracy:${accuracy(yTrain, predict(xTrain).argMax(1, true))}")
+            println("Accuracy:${accuracy(yTrain, predict(xTrain).argMax(1, true).asDouble())}")
         }
     }
 
@@ -230,7 +230,7 @@ fun main() = BroadcastDoubleTensorAlgebra {
     val prediction = model.predict(xTest)
 
     // process raw prediction via argMax
-    val predictionLabels = prediction.argMax(1, true)
+    val predictionLabels = prediction.argMax(1, true).asDouble()
 
     // find out accuracy
     val acc = accuracy(yTest, predictionLabels)

kmath-multik/src/main/kotlin/space/kscience/kmath/multik/MultikTensorAlgebra.kt

@@ -277,7 +277,7 @@ public abstract class MultikTensorAlgebra<T, A : Ring<T>> : TensorAlgebra<T, A>
         TODO("Not yet implemented")
     }
 
-    override fun StructureND<T>.argMax(dim: Int, keepDim: Boolean): Tensor<T> {
+    override fun StructureND<T>.argMax(dim: Int, keepDim: Boolean): Tensor<Int> {
         TODO("Not yet implemented")
     }
 }

kmath-nd4j/src/main/kotlin/space/kscience/kmath/nd4j/Nd4jTensorAlgebra.kt

@@ -108,8 +108,8 @@ public sealed interface Nd4jTensorAlgebra<T : Number, A : Field<T>> : AnalyticTe
     override fun Tensor<T>.view(shape: IntArray): Nd4jArrayStructure<T> = ndArray.reshape(shape).wrap()
     override fun Tensor<T>.viewAs(other: StructureND<T>): Nd4jArrayStructure<T> = view(other.shape)
 
-    override fun StructureND<T>.argMax(dim: Int, keepDim: Boolean): Nd4jArrayStructure<T> =
+    override fun StructureND<T>.argMax(dim: Int, keepDim: Boolean): Tensor<Int> =
-        ndBase.get().argmax(ndArray, keepDim, dim).wrap()
+        ndBase.get().argmax(ndArray, keepDim, dim).asIntStructure()
 
     override fun StructureND<T>.mean(dim: Int, keepDim: Boolean): Nd4jArrayStructure<T> =
         ndArray.mean(keepDim, dim).wrap()

kmath-tensors/src/commonMain/kotlin/space/kscience/kmath/tensors/api/TensorAlgebra.kt

@@ -324,7 +324,7 @@ public interface TensorAlgebra<T, A : Ring<T>> : RingOpsND<T, A> {
      * @param keepDim whether the output tensor has [dim] retained or not.
      * @return the index of maximum value of each row of the input tensor in the given dimension [dim].
      */
-    public fun StructureND<T>.argMax(dim: Int, keepDim: Boolean): Tensor<T>
+    public fun StructureND<T>.argMax(dim: Int, keepDim: Boolean): Tensor<Int>
 
     override fun add(left: StructureND<T>, right: StructureND<T>): Tensor<T> = left + right
 

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

@@ -9,7 +9,6 @@ import space.kscience.kmath.misc.PerformancePitfall
 import space.kscience.kmath.nd.Strides
 import space.kscience.kmath.structures.MutableBuffer
 import space.kscience.kmath.tensors.api.Tensor
-import space.kscience.kmath.tensors.core.internal.TensorLinearStructure
 
 /**
  * Represents [Tensor] over a [MutableBuffer] intended to be used through [DoubleTensor] and [IntTensor]

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

@@ -10,6 +10,7 @@ import space.kscience.kmath.nd.StructureND
 import space.kscience.kmath.nd.as1D
 import space.kscience.kmath.nd.as2D
 import space.kscience.kmath.operations.DoubleField
+import space.kscience.kmath.structures.MutableBuffer
 import space.kscience.kmath.structures.indices
 import space.kscience.kmath.tensors.api.AnalyticTensorAlgebra
 import space.kscience.kmath.tensors.api.LinearOpsTensorAlgebra
@@ -571,11 +572,11 @@ public open class DoubleTensorAlgebra :
     internal inline fun StructureND<Double>.fold(foldFunction: (DoubleArray) -> Double): Double =
         foldFunction(tensor.copyArray())
 
-    internal inline fun StructureND<Double>.foldDim(
+    internal inline fun <reified R: Any> StructureND<Double>.foldDim(
-        foldFunction: (DoubleArray) -> Double,
+        foldFunction: (DoubleArray) -> R,
         dim: Int,
         keepDim: Boolean,
-    ): DoubleTensor {
+    ): BufferedTensor<R> {
         check(dim < dimension) { "Dimension $dim out of range $dimension" }
         val resShape = if (keepDim) {
             shape.take(dim).toIntArray() + intArrayOf(1) + shape.takeLast(dimension - dim - 1).toIntArray()
@@ -583,37 +584,39 @@ public open class DoubleTensorAlgebra :
             shape.take(dim).toIntArray() + shape.takeLast(dimension - dim - 1).toIntArray()
         }
         val resNumElements = resShape.reduce(Int::times)
-        val resTensor = DoubleTensor(resShape, DoubleArray(resNumElements) { 0.0 }, 0)
+        val init = foldFunction(DoubleArray(1){0.0})
-        for (index in resTensor.indices.asSequence()) {
+        val resTensor = BufferedTensor(resShape,
+            MutableBuffer.auto(resNumElements) { init }, 0)
+        for (index in resTensor.indices) {
             val prefix = index.take(dim).toIntArray()
             val suffix = index.takeLast(dimension - dim - 1).toIntArray()
             resTensor[index] = foldFunction(DoubleArray(shape[dim]) { i ->
                 tensor[prefix + intArrayOf(i) + suffix]
             })
         }
-
         return resTensor
     }
 
     override fun StructureND<Double>.sum(): Double = tensor.fold { it.sum() }
 
     override fun StructureND<Double>.sum(dim: Int, keepDim: Boolean): DoubleTensor =
-        foldDim({ x -> x.sum() }, dim, keepDim)
+        foldDim({ x -> x.sum() }, dim, keepDim).toDoubleTensor()
 
     override fun StructureND<Double>.min(): Double = this.fold { it.minOrNull()!! }
 
     override fun StructureND<Double>.min(dim: Int, keepDim: Boolean): DoubleTensor =
-        foldDim({ x -> x.minOrNull()!! }, dim, keepDim)
+        foldDim({ x -> x.minOrNull()!! }, dim, keepDim).toDoubleTensor()
 
     override fun StructureND<Double>.max(): Double = this.fold { it.maxOrNull()!! }
 
     override fun StructureND<Double>.max(dim: Int, keepDim: Boolean): DoubleTensor =
-        foldDim({ x -> x.maxOrNull()!! }, dim, keepDim)
+        foldDim({ x -> x.maxOrNull()!! }, dim, keepDim).toDoubleTensor()
 
-    override fun StructureND<Double>.argMax(dim: Int, keepDim: Boolean): DoubleTensor =
+
+    override fun StructureND<Double>.argMax(dim: Int, keepDim: Boolean): IntTensor =
         foldDim({ x ->
-            x.withIndex().maxByOrNull { it.value }?.index!!.toDouble()
+            x.withIndex().maxByOrNull { it.value }?.index!!
-        }, dim, keepDim)
+        }, dim, keepDim).toIntTensor()
 
 
     override fun StructureND<Double>.mean(): Double = this.fold { it.sum() / tensor.numElements }
@@ -626,7 +629,7 @@ public open class DoubleTensorAlgebra :
             },
             dim,
             keepDim
-        )
+        ).toDoubleTensor()
 
     override fun StructureND<Double>.std(): Double = this.fold { arr ->
         val mean = arr.sum() / tensor.numElements
@@ -641,7 +644,7 @@ public open class DoubleTensorAlgebra :
         },
         dim,
         keepDim
-    )
+    ).toDoubleTensor()
 
     override fun StructureND<Double>.variance(): Double = this.fold { arr ->
         val mean = arr.sum() / tensor.numElements
@@ -656,7 +659,7 @@ public open class DoubleTensorAlgebra :
         },
         dim,
         keepDim
-    )
+    ).toDoubleTensor()
 
     private fun cov(x: DoubleTensor, y: DoubleTensor): Double {
         val n = x.shape[0]

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

@@ -6,6 +6,7 @@
 package space.kscience.kmath.tensors.core
 
 import space.kscience.kmath.structures.IntBuffer
+import space.kscience.kmath.tensors.core.internal.array
 
 /**
  * Default [BufferedTensor] implementation for [Int] values
@@ -14,4 +15,7 @@ public class IntTensor internal constructor(
     shape: IntArray,
     buffer: IntArray,
     offset: Int = 0
-) : BufferedTensor<Int>(shape, IntBuffer(buffer), offset)
+) : BufferedTensor<Int>(shape, IntBuffer(buffer), offset){
+    public fun asDouble() : DoubleTensor =
+        DoubleTensor(shape, mutableBuffer.array().map{ it.toDouble()}.toDoubleArray(), bufferStart)
+}

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

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2018-2021 KMath contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package space.kscience.kmath.tensors.core
+
+import space.kscience.kmath.nd.Strides
+import kotlin.math.max
+
+/**
+ * This [Strides] implementation follows the last dimension first convention
+ * For more information: https://numpy.org/doc/stable/reference/generated/numpy.ndarray.strides.html
+ *
+ * @param shape the shape of the tensor.
+ */
+public class TensorLinearStructure(override val shape: IntArray) : Strides() {
+    override val strides: IntArray
+        get() = stridesFromShape(shape)
+
+    override fun index(offset: Int): IntArray =
+        indexFromOffset(offset, strides, shape.size)
+
+    override val linearSize: Int
+        get() = shape.reduce(Int::times)
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other == null || this::class != other::class) return false
+
+        other as TensorLinearStructure
+
+        if (!shape.contentEquals(other.shape)) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        return shape.contentHashCode()
+    }
+
+    public companion object {
+
+        public fun stridesFromShape(shape: IntArray): IntArray {
+            val nDim = shape.size
+            val res = IntArray(nDim)
+            if (nDim == 0)
+                return res
+
+            var current = nDim - 1
+            res[current] = 1
+
+            while (current > 0) {
+                res[current - 1] = max(1, shape[current]) * res[current]
+                current--
+            }
+            return res
+        }
+
+        public fun indexFromOffset(offset: Int, strides: IntArray, nDim: Int): IntArray {
+            val res = IntArray(nDim)
+            var current = offset
+            var strideIndex = 0
+
+            while (strideIndex < nDim) {
+                res[strideIndex] = (current / strides[strideIndex])
+                current %= strides[strideIndex]
+                strideIndex++
+            }
+            return res
+        }
+    }
+
+}

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

@@ -1,71 +0,0 @@
-/*
- * Copyright 2018-2021 KMath contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
- */
-
-package space.kscience.kmath.tensors.core.internal
-
-import space.kscience.kmath.nd.Strides
-import kotlin.math.max
-
-
-internal fun stridesFromShape(shape: IntArray): IntArray {
-    val nDim = shape.size
-    val res = IntArray(nDim)
-    if (nDim == 0)
-        return res
-
-    var current = nDim - 1
-    res[current] = 1
-
-    while (current > 0) {
-        res[current - 1] = max(1, shape[current]) * res[current]
-        current--
-    }
-    return res
-}
-
-internal fun indexFromOffset(offset: Int, strides: IntArray, nDim: Int): IntArray {
-    val res = IntArray(nDim)
-    var current = offset
-    var strideIndex = 0
-
-    while (strideIndex < nDim) {
-        res[strideIndex] = (current / strides[strideIndex])
-        current %= strides[strideIndex]
-        strideIndex++
-    }
-    return res
-}
-
-/**
- * This [Strides] implementation follows the last dimension first convention
- * For more information: https://numpy.org/doc/stable/reference/generated/numpy.ndarray.strides.html
- *
- * @param shape the shape of the tensor.
- */
-internal class TensorLinearStructure(override val shape: IntArray) : Strides() {
-    override val strides: IntArray
-        get() = stridesFromShape(shape)
-
-    override fun index(offset: Int): IntArray =
-        indexFromOffset(offset, strides, shape.size)
-
-    override val linearSize: Int
-        get() = shape.reduce(Int::times)
-
-    override fun equals(other: Any?): Boolean {
-        if (this === other) return true
-        if (other == null || this::class != other::class) return false
-
-        other as TensorLinearStructure
-
-        if (!shape.contentEquals(other.shape)) return false
-
-        return true
-    }
-
-    override fun hashCode(): Int {
-        return shape.contentHashCode()
-    }
-}

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

@@ -12,6 +12,7 @@ import space.kscience.kmath.tensors.api.Tensor
 import space.kscience.kmath.tensors.core.BufferedTensor
 import space.kscience.kmath.tensors.core.DoubleTensor
 import space.kscience.kmath.tensors.core.IntTensor
+import space.kscience.kmath.tensors.core.TensorLinearStructure
 
 internal fun BufferedTensor<Int>.asTensor(): IntTensor =
     IntTensor(this.shape, this.mutableBuffer.array(), this.bufferStart)