Rename Tensor::get to Tensor::getTensor to avoid name clash.

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

@@ -58,7 +58,7 @@ fun main(): Unit = Double.tensorAlgebra.withBroadcast {  // work in context with
 
     // and find out eigenvector of it
     val (_, evecs) = covMatrix.symEig()
-    val v = evecs[0]
+    val v = evecs.getTensor(0)
     println("Eigenvector:\n$v")
 
     // reduce dimension of dataset
@@ -68,7 +68,7 @@ fun main(): Unit = Double.tensorAlgebra.withBroadcast {  // work in context with
     // we can restore original data from reduced data;
     // for example, find 7th element of dataset.
     val n = 7
-    val restored = (datasetReduced[n] dot v.view(intArrayOf(1, 2))) * std + mean
-    println("Original value:\n${dataset[n]}")
+    val restored = (datasetReduced.getTensor(n) dot v.view(intArrayOf(1, 2))) * std + mean
+    println("Original value:\n${dataset.getTensor(n)}")
     println("Restored value:\n$restored")
 }

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

@@ -66,7 +66,7 @@ fun main() = Double.tensorAlgebra.withBroadcast {// work in context with linear
         val n = l.shape[0]
         val x = zeros(intArrayOf(n))
         for (i in 0 until n) {
-            x[intArrayOf(i)] = (b[intArrayOf(i)] - l[i].dot(x).value()) / l[intArrayOf(i, i)]
+            x[intArrayOf(i)] = (b[intArrayOf(i)] - l.getTensor(i).dot(x).value()) / l[intArrayOf(i, i)]
         }
         return x
     }

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

@@ -197,7 +197,7 @@ fun main() = BroadcastDoubleTensorAlgebra {
     val y = fromArray(
         intArrayOf(sampleSize, 1),
         DoubleArray(sampleSize) { i ->
-            if (x[i].sum() > 0.0) {
+            if (x.getTensor(i).sum() > 0.0) {
                 1.0
             } else {
                 0.0

kmath-core/src/commonMain/kotlin/space/kscience/kmath/misc/cumulative.kt

@@ -7,6 +7,7 @@ package space.kscience.kmath.misc
 
 import space.kscience.kmath.operations.Ring
 import space.kscience.kmath.operations.invoke
+import space.kscience.kmath.structures.Buffer
 import kotlin.jvm.JvmName
 
 /**
@@ -42,8 +43,8 @@ public inline fun <T, R> List<T>.cumulative(initial: R, crossinline operation: (
 /**
  * Cumulative sum with custom space
  */
-public fun <T> Iterable<T>.cumulativeSum(group: Ring<T>): Iterable<T> =
-    group { cumulative(zero) { element: T, sum: T -> sum + element } }
+public fun <T> Iterable<T>.cumulativeSum(ring: Ring<T>): Iterable<T> =
+    ring { cumulative(zero) { element: T, sum: T -> sum + element } }
 
 @JvmName("cumulativeSumOfDouble")
 public fun Iterable<Double>.cumulativeSum(): Iterable<Double> = cumulative(0.0) { element, sum -> sum + element }
@@ -54,8 +55,8 @@ public fun Iterable<Int>.cumulativeSum(): Iterable<Int> = cumulative(0) { elemen
 @JvmName("cumulativeSumOfLong")
 public fun Iterable<Long>.cumulativeSum(): Iterable<Long> = cumulative(0L) { element, sum -> sum + element }
 
-public fun <T> Sequence<T>.cumulativeSum(group: Ring<T>): Sequence<T> =
-    group { cumulative(zero) { element: T, sum: T -> sum + element } }
+public fun <T> Sequence<T>.cumulativeSum(ring: Ring<T>): Sequence<T> =
+    ring { cumulative(zero) { element: T, sum: T -> sum + element } }
 
 @JvmName("cumulativeSumOfDouble")
 public fun Sequence<Double>.cumulativeSum(): Sequence<Double> = cumulative(0.0) { element, sum -> sum + element }
@@ -77,3 +78,12 @@ public fun List<Int>.cumulativeSum(): List<Int> = cumulative(0) { element, sum -
 
 @JvmName("cumulativeSumOfLong")
 public fun List<Long>.cumulativeSum(): List<Long> = cumulative(0L) { element, sum -> sum + element }
+
+
+public fun <T> Buffer<T>.cumulativeSum(ring: Ring<T>): Buffer<T> = with(ring) {
+    var accumulator: T = zero
+    return bufferFactory(size) {
+        accumulator += get(it)
+        accumulator
+    }
+}

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

@@ -185,7 +185,7 @@ public abstract class MultikTensorAlgebra<T, A : Ring<T>>(
     override fun StructureND<T>.unaryMinus(): MultikTensor<T> =
         asMultik().array.unaryMinus().wrap()
 
-    override fun Tensor<T>.get(i: Int): MultikTensor<T> = asMultik().array.mutableView(i).wrap()
+    override fun Tensor<T>.getTensor(i: Int): MultikTensor<T> = asMultik().array.mutableView(i).wrap()
 
     override fun Tensor<T>.transpose(i: Int, j: Int): MultikTensor<T> = asMultik().array.transpose(i, j).wrap()
 
@@ -246,6 +246,12 @@ public abstract class MultikTensorAlgebra<T, A : Ring<T>>(
         return multikMath.minDN(asMultik().array, dim).wrap()
     }
 
+    override fun StructureND<T>.argMin(dim: Int, keepDim: Boolean): Tensor<Int> {
+        if (keepDim) TODO("keepDim not implemented")
+        val res = multikMath.argMinDN(asMultik().array, dim)
+        return with(MultikIntAlgebra(multikEngine)) { res.wrap() }
+    }
+
     override fun StructureND<T>.max(): T? = asMultik().array.max()
 
     override fun StructureND<T>.max(dim: Int, keepDim: Boolean): Tensor<T> {

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

@@ -95,7 +95,7 @@ public sealed interface Nd4jTensorAlgebra<T : Number, A : Field<T>> : AnalyticTe
     }
 
     override fun StructureND<T>.unaryMinus(): Nd4jArrayStructure<T> = ndArray.neg().wrap()
-    override fun Tensor<T>.get(i: Int): Nd4jArrayStructure<T> = ndArray.slice(i.toLong()).wrap()
+    override fun Tensor<T>.getTensor(i: Int): Nd4jArrayStructure<T> = ndArray.slice(i.toLong()).wrap()
     override fun Tensor<T>.transpose(i: Int, j: Int): Nd4jArrayStructure<T> = ndArray.swapAxes(i, j).wrap()
     override fun StructureND<T>.dot(other: StructureND<T>): Nd4jArrayStructure<T> = ndArray.mmul(other.ndArray).wrap()
 
@@ -111,6 +111,9 @@ 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>.argMin(dim: Int, keepDim: Boolean): Tensor<Int> =
+        ndBase.get().argmin(ndArray, keepDim, dim).asIntStructure()
+
     override fun StructureND<T>.argMax(dim: Int, keepDim: Boolean): Tensor<Int> =
         ndBase.get().argmax(ndArray, keepDim, dim).asIntStructure()
 

kmath-tensorflow/src/main/kotlin/space/kscience/kmath/tensorflow/TensorFlowAlgebra.kt

@@ -184,7 +184,7 @@ public abstract class TensorFlowAlgebra<T, TT : TNumber, A : Ring<T>> internal c
 
     override fun StructureND<T>.unaryMinus(): TensorFlowOutput<T, TT> = operate(ops.math::neg)
 
-    override fun Tensor<T>.get(i: Int): Tensor<T> = operate {
+    override fun Tensor<T>.getTensor(i: Int): Tensor<T> = operate {
         StridedSliceHelper.stridedSlice(ops.scope(), it, Indices.at(i.toLong()))
     }
 
@@ -238,6 +238,11 @@ public abstract class TensorFlowAlgebra<T, TT : TNumber, A : Ring<T>> internal c
         ops.min(it, ops.constant(dim), Min.keepDims(keepDim))
     }
 
+    override fun StructureND<T>.argMin(dim: Int, keepDim: Boolean): Tensor<Int> = IntTensorFlowOutput(
+        graph,
+        ops.math.argMin(asTensorFlow().output, ops.constant(dim), TInt32::class.java).output()
+    ).actualTensor
+
     override fun StructureND<T>.max(): T = operate {
         ops.max(it, ops.constant(intArrayOf()))
     }.value()

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

@@ -166,7 +166,11 @@ public interface TensorAlgebra<T, A : Ring<T>> : RingOpsND<T, A> {
      * @param i index of the extractable tensor
      * @return subtensor of the original tensor with index [i]
      */
-    public operator fun Tensor<T>.get(i: Int): Tensor<T>
+    public fun Tensor<T>.getTensor(i: Int): Tensor<T>
+
+    public fun Tensor<T>.getTensor(first: Int, second: Int): Tensor<T> {
+        return getTensor(first).getTensor(second)
+    }
 
     /**
      * Returns a tensor that is a transposed version of this tensor. The given dimensions [i] and [j] are swapped.
@@ -286,6 +290,19 @@ public interface TensorAlgebra<T, A : Ring<T>> : RingOpsND<T, A> {
      */
     public fun StructureND<T>.min(dim: Int, keepDim: Boolean): Tensor<T>
 
+    /**
+     * Returns the index of minimum value of each row of the input tensor in the given dimension [dim].
+     *
+     * If [keepDim] is true, the output tensor is of the same size as
+     * input except in the dimension [dim] where it is of size 1.
+     * Otherwise, [dim] is squeezed, resulting in the output tensor having 1 fewer dimension.
+     *
+     * @param dim the dimension to reduce.
+     * @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>.argMin(dim: Int, keepDim: Boolean): Tensor<Int>
+
     /**
      * Returns the maximum value of all elements in the input tensor or null if there are no values
      */
@@ -320,4 +337,4 @@ public interface TensorAlgebra<T, A : Ring<T>> : RingOpsND<T, A> {
     override fun add(left: StructureND<T>, right: StructureND<T>): Tensor<T> = left + right
 
     override fun multiply(left: StructureND<T>, right: StructureND<T>): Tensor<T> = left * right
-}
+}

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

@@ -24,6 +24,7 @@ import kotlin.math.*
 /**
  * Implementation of basic operations over double tensors and basic algebra operations on them.
  */
+@OptIn(PerformancePitfall::class)
 public open class DoubleTensorAlgebra :
     TensorPartialDivisionAlgebra<Double, DoubleField>,
     AnalyticTensorAlgebra<Double, DoubleField>,
@@ -120,7 +121,7 @@ public open class DoubleTensorAlgebra :
         TensorLinearStructure(shape).asSequence().map { DoubleField.initializer(it) }.toMutableList().toDoubleArray()
     )
 
-    override operator fun Tensor<Double>.get(i: Int): DoubleTensor {
+    override fun Tensor<Double>.getTensor(i: Int): DoubleTensor {
         val lastShape = asDoubleTensor().shape.drop(1).toIntArray()
         val newShape = if (lastShape.isNotEmpty()) lastShape else intArrayOf(1)
         val newStart = newShape.reduce(Int::times) * i + asDoubleTensor().bufferStart
@@ -204,7 +205,11 @@ public open class DoubleTensorAlgebra :
      * @return a copy of the `input` tensor with a copied buffer.
      */
     public fun StructureND<Double>.copy(): DoubleTensor =
-        DoubleTensor(asDoubleTensor().shape, asDoubleTensor().mutableBuffer.array().copyOf(), asDoubleTensor().bufferStart)
+        DoubleTensor(
+            asDoubleTensor().shape,
+            asDoubleTensor().mutableBuffer.array().copyOf(),
+            asDoubleTensor().bufferStart
+        )
 
     override fun Double.plus(arg: StructureND<Double>): DoubleTensor {
         val resBuffer = DoubleArray(arg.asDoubleTensor().numElements) { i ->
@@ -413,7 +418,10 @@ public open class DoubleTensorAlgebra :
     @UnstableKMathAPI
     public infix fun StructureND<Double>.matmul(other: StructureND<Double>): DoubleTensor {
         if (asDoubleTensor().shape.size == 1 && other.shape.size == 1) {
-            return DoubleTensor(intArrayOf(1), doubleArrayOf(asDoubleTensor().times(other).asDoubleTensor().mutableBuffer.array().sum()))
+            return DoubleTensor(
+                intArrayOf(1),
+                doubleArrayOf(asDoubleTensor().times(other).asDoubleTensor().mutableBuffer.array().sum())
+            )
         }
 
         var newThis = asDoubleTensor().copy()
@@ -592,7 +600,8 @@ public open class DoubleTensorAlgebra :
         check(tensors.all { it.shape contentEquals shape }) { "Tensors must have same shapes" }
         val resShape = intArrayOf(tensors.size) + shape
         val resBuffer = tensors.flatMap {
-            it.asDoubleTensor().mutableBuffer.array().drop(it.asDoubleTensor().bufferStart).take(it.asDoubleTensor().numElements)
+            it.asDoubleTensor().mutableBuffer.array().drop(it.asDoubleTensor().bufferStart)
+                .take(it.asDoubleTensor().numElements)
         }.toDoubleArray()
         return DoubleTensor(resShape, resBuffer, 0)
     }
@@ -603,7 +612,7 @@ public open class DoubleTensorAlgebra :
      * @param indices the [IntArray] of 1-dimensional indices
      * @return tensor with rows corresponding to row by [indices]
      */
-    public fun Tensor<Double>.rowsByIndices(indices: IntArray): DoubleTensor = stack(indices.map { this[it] })
+    public fun Tensor<Double>.rowsByIndices(indices: IntArray): DoubleTensor = stack(indices.map { getTensor(it) })
 
     private inline fun StructureND<Double>.fold(foldFunction: (DoubleArray) -> Double): Double =
         foldFunction(asDoubleTensor().copyArray())
@@ -645,6 +654,10 @@ public open class DoubleTensorAlgebra :
     override fun StructureND<Double>.min(dim: Int, keepDim: Boolean): DoubleTensor =
         foldDim(dim, keepDim) { x -> x.minOrNull()!! }.asDoubleTensor()
 
+    override fun StructureND<Double>.argMin(dim: Int, keepDim: Boolean): Tensor<Int> = foldDim(dim, keepDim) { x ->
+        x.withIndex().minByOrNull { it.value }?.index!!
+    }.asIntTensor()
+
     override fun StructureND<Double>.max(): Double = this.fold { it.maxOrNull()!! }
 
     override fun StructureND<Double>.max(dim: Int, keepDim: Boolean): DoubleTensor =

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

@@ -118,7 +118,7 @@ public open class IntTensorAlgebra : TensorAlgebra<Int, IntRing> {
         TensorLinearStructure(shape).asSequence().map { IntRing.initializer(it) }.toMutableList().toIntArray()
     )
 
-    override operator fun Tensor<Int>.get(i: Int): IntTensor {
+    override fun Tensor<Int>.getTensor(i: Int): IntTensor {
         val lastShape = asIntTensor().shape.drop(1).toIntArray()
         val newShape = if (lastShape.isNotEmpty()) lastShape else intArrayOf(1)
         val newStart = newShape.reduce(Int::times) * i + asIntTensor().bufferStart
@@ -433,7 +433,7 @@ public open class IntTensorAlgebra : TensorAlgebra<Int, IntRing> {
      * @param indices the [IntArray] of 1-dimensional indices
      * @return tensor with rows corresponding to row by [indices]
      */
-    public fun Tensor<Int>.rowsByIndices(indices: IntArray): IntTensor = stack(indices.map { this[it] })
+    public fun Tensor<Int>.rowsByIndices(indices: IntArray): IntTensor = stack(indices.map { getTensor(it) })
 
     private inline fun StructureND<Int>.fold(foldFunction: (IntArray) -> Int): Int =
         foldFunction(asIntTensor().copyArray())
@@ -475,6 +475,11 @@ public open class IntTensorAlgebra : TensorAlgebra<Int, IntRing> {
     override fun StructureND<Int>.min(dim: Int, keepDim: Boolean): IntTensor =
         foldDim(dim, keepDim) { x -> x.minOrNull()!! }.asIntTensor()
 
+    override fun StructureND<Int>.argMin(dim: Int, keepDim: Boolean): IntTensor =
+        foldDim(dim, keepDim) { x ->
+            x.withIndex().minByOrNull { it.value }?.index!!
+        }.asIntTensor()
+
     override fun StructureND<Int>.max(): Int = this.fold { it.maxOrNull()!! }
 
     override fun StructureND<Int>.max(dim: Int, keepDim: Boolean): IntTensor =

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

@@ -257,13 +257,13 @@ internal fun DoubleTensorAlgebra.qrHelper(
     val qT = q.transpose(0, 1)
 
     for (j in 0 until n) {
-        val v = matrixT[j]
+        val v = matrixT.getTensor(j)
         val vv = v.as1D()
         if (j > 0) {
             for (i in 0 until j) {
-                r[i, j] = (qT[i] dot matrixT[j]).value()
+                r[i, j] = (qT.getTensor(i) dot matrixT.getTensor(j)).value()
                 for (k in 0 until n) {
-                    val qTi = qT[i].as1D()
+                    val qTi = qT.getTensor(i).as1D()
                     vv[k] = vv[k] - r[i, j] * qTi[k]
                 }
             }
@@ -313,7 +313,7 @@ internal fun DoubleTensorAlgebra.svdHelper(
             val outerProduct = DoubleArray(u.shape[0] * v.shape[0])
             for (i in 0 until u.shape[0]) {
                 for (j in 0 until v.shape[0]) {
-                    outerProduct[i * v.shape[0] + j] = u[i].value() * v[j].value()
+                    outerProduct[i * v.shape[0] + j] = u.getTensor(i).value() * v.getTensor(j).value()
                 }
             }
             a = a - singularValue.times(DoubleTensor(intArrayOf(u.shape[0], v.shape[0]), outerProduct))

kmath-tensors/src/commonTest/kotlin/space/kscience/kmath/tensors/core/TestDoubleTensor.kt

@@ -36,17 +36,18 @@ internal class TestDoubleTensor {
         val tensor = fromArray(intArrayOf(2, 2), doubleArrayOf(3.5, 5.8, 58.4, 2.4))
         assertEquals(tensor[intArrayOf(0, 1)], 5.8)
         assertTrue(
-            tensor.elements().map { it.second }.toList().toDoubleArray() contentEquals tensor.mutableBuffer.toDoubleArray()
+            tensor.elements().map { it.second }.toList()
+                .toDoubleArray() contentEquals tensor.mutableBuffer.toDoubleArray()
         )
     }
 
     @Test
     fun testGet() = DoubleTensorAlgebra {
         val tensor = fromArray(intArrayOf(1, 2, 2), doubleArrayOf(3.5, 5.8, 58.4, 2.4))
-        val matrix = tensor[0].as2D()
+        val matrix = tensor.getTensor(0).as2D()
         assertEquals(matrix[0, 1], 5.8)
 
-        val vector = tensor[0][1].as1D()
+        val vector = tensor.getTensor(0, 1).as1D()
         assertEquals(vector[0], 58.4)
 
         matrix[0, 1] = 77.89
@@ -57,8 +58,8 @@ internal class TestDoubleTensor {
 
         tensor.matrixSequence().forEach {
             val a = it.toTensor()
-            val secondRow = a[1].as1D()
-            val secondColumn = a.transpose(0, 1)[1].as1D()
+            val secondRow = a.getTensor(1).as1D()
+            val secondColumn = a.transpose(0, 1).getTensor(1).as1D()
             assertEquals(secondColumn[0], 77.89)
             assertEquals(secondRow[1], secondColumn[1])
         }