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

@@ -69,7 +69,7 @@ fun main () {
             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).valueOrNull()!!) / l[intArrayOf(i, i)]
+                x[intArrayOf(i)] = (b[intArrayOf(i)] -  l[i].dot(x).value()) / l[intArrayOf(i, i)]
             }
             return x
         }

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

@@ -60,7 +60,7 @@ fun main() {
             require(yTrue.shape contentEquals yPred.shape)
 
             val diff = yTrue - yPred
-            return diff.dot(diff).sqrt().valueOrNull()!!
+            return diff.dot(diff).sqrt().value()
         }
 
         println("MSE: ${mse(alpha, alphaOLS)}")

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

@@ -15,13 +15,21 @@ import space.kscience.kmath.operations.Algebra
  */
 public interface TensorAlgebra<T>: Algebra<Tensor<T>> {
 
+    /**
+     *
+     * Returns a single tensor value of unit dimension if tensor shape equals to [1].
+     *
+     * @return a nullable value of a potentially scalar tensor.
+     */
+    public fun Tensor<T>.valueOrNull(): T?
+
     /**
      *
      * Returns a single tensor value of unit dimension. The tensor shape must be equal to [1].
      *
      * @return the value of a scalar tensor.
      */
-    public fun Tensor<T>.valueOrNull(): T?
+    public fun Tensor<T>.value(): T
 
     /**
      * Each element of the tensor [other] is added to this value.

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

@@ -35,10 +35,11 @@ public open class DoubleTensorAlgebra :
 
     public companion object : DoubleTensorAlgebra()
 
-    override fun Tensor<Double>.valueOrNull(): Double? = if(tensor.shape contentEquals intArrayOf(1)) {
-            // Inconsistent value for tensor of with this shape
-            tensor.mutableBuffer.array()[tensor.bufferStart]
-        } else null
+    override fun Tensor<Double>.valueOrNull(): Double? = if (tensor.shape contentEquals intArrayOf(1))
+        tensor.mutableBuffer.array()[tensor.bufferStart] else null
+
+    override fun Tensor<Double>.value(): Double =
+        valueOrNull() ?: throw IllegalArgumentException("Inconsistent value for tensor of with $shape shape")
 
     /**
      * Constructs a tensor with the specified shape and data.
@@ -62,8 +63,10 @@ public open class DoubleTensorAlgebra :
      * @return tensor with the [shape] shape and data generated by the [initializer].
      */
     public fun produce(shape: IntArray, initializer: (IntArray) -> Double): DoubleTensor =
-        fromArray(shape,
-            TensorLinearStructure(shape).indices().map(initializer).toMutableList().toDoubleArray())
+        fromArray(
+            shape,
+            TensorLinearStructure(shape).indices().map(initializer).toMutableList().toDoubleArray()
+        )
 
     override operator fun Tensor<Double>.get(i: Int): DoubleTensor {
         val lastShape = tensor.shape.drop(1).toIntArray()
@@ -779,8 +782,10 @@ public open class DoubleTensorAlgebra :
         val qTensor = zeroesLike()
         val rTensor = zeroesLike()
         tensor.matrixSequence()
-            .zip((qTensor.matrixSequence()
-                .zip(rTensor.matrixSequence()))).forEach { (matrix, qr) ->
+            .zip(
+                (qTensor.matrixSequence()
+                    .zip(rTensor.matrixSequence()))
+            ).forEach { (matrix, qr) ->
                 val (q, r) = qr
                 qrHelper(matrix.asTensor(), q.asTensor(), r.as2D())
             }
@@ -812,9 +817,13 @@ public open class DoubleTensorAlgebra :
         val vTensor = zeros(commonShape + intArrayOf(min(n, m), m))
 
         tensor.matrixSequence()
-            .zip(uTensor.matrixSequence()
-                .zip(sTensor.vectorSequence()
-                    .zip(vTensor.matrixSequence()))).forEach { (matrix, USV) ->
+            .zip(
+                uTensor.matrixSequence()
+                    .zip(
+                        sTensor.vectorSequence()
+                            .zip(vTensor.matrixSequence())
+                    )
+            ).forEach { (matrix, USV) ->
                 val matrixSize = matrix.shape.reduce { acc, i -> acc * i }
                 val curMatrix = DoubleTensor(
                     matrix.shape,
@@ -918,10 +927,11 @@ public open class DoubleTensorAlgebra :
      * @return triple of P, L and U tensors
      */
     public fun Tensor<Double>.lu(epsilon: Double = 1e-9): Triple<DoubleTensor, DoubleTensor, DoubleTensor> {
-        val (lu, pivots) = this.luFactor(epsilon)
+        val (lu, pivots) = tensor.luFactor(epsilon)
         return luPivot(lu, pivots)
     }
 
     override fun Tensor<Double>.lu(): Triple<DoubleTensor, DoubleTensor, DoubleTensor> = lu(1e-9)
-
 }
+
+

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

@@ -58,7 +58,7 @@ internal fun DoubleTensorAlgebra.checkSymmetric(
 internal fun DoubleTensorAlgebra.checkPositiveDefinite(tensor: DoubleTensor, epsilon: Double = 1e-6) {
     checkSymmetric(tensor, epsilon)
     for (mat in tensor.matrixSequence())
-        check(mat.asTensor().detLU().valueOrNull()!! > 0.0) {
-            "Tensor contains matrices which are not positive definite ${mat.asTensor().detLU().valueOrNull()!!}"
+        check(mat.asTensor().detLU().value() > 0.0) {
+            "Tensor contains matrices which are not positive definite ${mat.asTensor().detLU().value()}"
         }
 }

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

@@ -240,14 +240,14 @@ internal fun DoubleTensorAlgebra.qrHelper(
         val vv = v.as1D()
         if (j > 0) {
             for (i in 0 until j) {
-                r[i, j] = (qT[i] dot matrixT[j]).valueOrNull()!!
+                r[i, j] = (qT[i] dot matrixT[j]).value()
                 for (k in 0 until n) {
                     val qTi = qT[i].as1D()
                     vv[k] = vv[k] - r[i, j] * qTi[k]
                 }
             }
         }
-        r[j, j] = DoubleTensorAlgebra { (v dot v).sqrt().valueOrNull()!! }
+        r[j, j] = DoubleTensorAlgebra { (v dot v).sqrt().value() }
         for (i in 0 until n) {
             qM[i, j] = vv[i] / r[j, j]
         }
@@ -270,9 +270,9 @@ internal fun DoubleTensorAlgebra.svd1d(a: DoubleTensor, epsilon: Double = 1e-10)
     while (true) {
         lastV = v
         v = b.dot(lastV)
-        val norm = DoubleTensorAlgebra { (v dot v).sqrt().valueOrNull()!! }
+        val norm = DoubleTensorAlgebra { (v dot v).sqrt().value() }
         v = v.times(1.0 / norm)
-        if (abs(v.dot(lastV).valueOrNull()!!) > 1 - epsilon) {
+        if (abs(v.dot(lastV).value()) > 1 - epsilon) {
             return v
         }
     }
@@ -293,7 +293,7 @@ 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].valueOrNull()!! * v[j].valueOrNull()!!
+                    outerProduct[i * v.shape[0] + j] = u[i].value() * v[j].value()
                 }
             }
             a = a - singularValue.times(DoubleTensor(intArrayOf(u.shape[0], v.shape[0]), outerProduct))
@@ -304,12 +304,12 @@ internal fun DoubleTensorAlgebra.svdHelper(
         if (n > m) {
             v = svd1d(a, epsilon)
             u = matrix.dot(v)
-            norm = DoubleTensorAlgebra { (u dot u).sqrt().valueOrNull()!! }
+            norm = DoubleTensorAlgebra { (u dot u).sqrt().value() }
             u = u.times(1.0 / norm)
         } else {
             u = svd1d(a, epsilon)
             v = matrix.transpose(0, 1).dot(u)
-            norm = DoubleTensorAlgebra { (v dot v).sqrt().valueOrNull()!! }
+            norm = DoubleTensorAlgebra { (v dot v).sqrt().value() }
             v = v.times(1.0 / norm)
         }
 

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

@@ -46,7 +46,7 @@ internal class TestDoubleLinearOpsTensorAlgebra {
             )
         )
 
-        assertTrue { abs(m.det().valueOrNull()!! - expectedValue) < 1e-5 }
+        assertTrue { abs(m.det().value() - expectedValue) < 1e-5 }
     }
 
     @Test
@@ -58,7 +58,7 @@ internal class TestDoubleLinearOpsTensorAlgebra {
             )
         )
 
-        assertTrue { abs(m.det().valueOrNull()!! - expectedValue) < 1e-5 }
+        assertTrue { abs(m.det().value() - expectedValue) < 1e-5 }
     }
 
     @Test
@@ -90,7 +90,7 @@ internal class TestDoubleLinearOpsTensorAlgebra {
     fun testScalarProduct() = DoubleTensorAlgebra {
         val a = fromArray(intArrayOf(3), doubleArrayOf(1.8, 2.5, 6.8))
         val b = fromArray(intArrayOf(3), doubleArrayOf(5.5, 2.6, 6.4))
-        assertEquals(a.dot(b).valueOrNull()!!, 59.92)
+        assertEquals(a.dot(b).value(), 59.92)
     }
 
     @Test

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

@@ -21,7 +21,7 @@ internal class TestDoubleTensor {
     fun testValue() = DoubleTensorAlgebra {
         val value = 12.5
         val tensor = fromArray(intArrayOf(1), doubleArrayOf(value))
-        assertEquals(tensor.valueOrNull()!!, value)
+        assertEquals(tensor.value(), value)
     }
 
     @Test