Grid generators for 1D double array

kmath-common/src/main/kotlin/scientifik/kmath/misc/Grids.kt

@@ -0,0 +1,40 @@
+package scientifik.kmath.misc
+
+import kotlin.coroutines.experimental.buildSequence
+
+
+/**
+ * Convert double range to sequence.
+ *
+ * If the step is positive, than the sequence starts with the lower boundary and increments by [step] until current value is lower than upper boundary.
+ * The boundary itself is not necessary included.
+ *
+ * If step is negative, the same goes from upper boundary downwards
+ */
+fun ClosedFloatingPointRange<Double>.toSequence(step: Double): Sequence<Double> {
+    return when {
+        step == 0.0 -> error("Zero step in double progression")
+        step > 0 -> buildSequence {
+            var current = start
+            while (current <= endInclusive) {
+                yield(current)
+                current += step
+            }
+        }
+        else -> buildSequence {
+            var current = endInclusive
+            while (current >= start) {
+                yield(current)
+                current += step
+            }
+        }
+    }
+}
+
+/**
+ * Convert double range to array of evenly spaced doubles, where the size of array equals [numPoints]
+ */
+fun ClosedFloatingPointRange<Double>.toGrid(numPoints: Int): DoubleArray {
+    if (numPoints < 2) error("Can't create grid with less than two points")
+    return DoubleArray(numPoints) { i -> start + (endInclusive - start) / (numPoints - 1) * i }
+}

kmath-common/src/main/kotlin/scientifik/kmath/structures/BufferNDField.kt

@@ -40,11 +40,12 @@ abstract class BufferNDField<T>(shape: List<Int>, field: Field<T>) : NDField<T>(
         }.sum()
     }
 
-    protected fun index(offset: Int): List<Int>{
+    //TODO introduce a fast way to calculate index of the next element?
+    protected fun index(offset: Int): List<Int> {
         return buildSequence {
             var current = offset
-            var strideIndex = strides.size-2
-            while (strideIndex>=0){
+            var strideIndex = strides.size - 2
+            while (strideIndex >= 0) {
                 yield(current / strides[strideIndex])
                 current %= strides[strideIndex]
                 strideIndex--
@@ -59,7 +60,7 @@ abstract class BufferNDField<T>(shape: List<Int>, field: Field<T>) : NDField<T>(
     protected abstract fun createBuffer(capacity: Int, initializer: (Int) -> T): Buffer<T>
 
     override fun produce(initializer: (List<Int>) -> T): NDArray<T> {
-        val buffer = createBuffer(capacity){initializer(index(it))}
+        val buffer = createBuffer(capacity) { initializer(index(it)) }
         return BufferNDArray(this, buffer)
     }
 

kmath-jvm/build.gradle

@@ -22,3 +22,9 @@ compileTestKotlin {
     kotlinOptions.jvmTarget = "1.8"
 }
 sourceCompatibility = "1.8"
+
+kotlin {
+    experimental {
+        coroutines "enable"
+    }
+}