implement UpSampling1D/2D/3D layers, with tests

src/layers/convolutional/UpSampling2D.js

@@ -0,0 +1,58 @@
+import Layer from '../../engine/Layer'
+import Tensor from '../../Tensor'
+import ops from 'ndarray-ops'
+
+/**
+ * UpSampling2D layer class
+ */
+export default class UpSampling2D extends Layer {
+  /**
+   * Creates a UpSampling2D activation layer
+   * @param {number} size - upsampling factor
+   */
+  constructor (size = [2, 2], attrs = {}) {
+    super(attrs)
+    const {
+      dimOrdering = 'tf'
+    } = attrs
+
+    this.size = size
+    this.dimOrdering = dimOrdering
+  }
+
+  /**
+   * Method for layer computational logic
+   * @param {Tensor} x
+   * @returns {Tensor} x
+   */
+  call = x => {
+    // convert to tf ordering
+    if (this.dimOrdering === 'th') {
+      x.tensor = x.tensor.transpose(1, 2, 0)
+    }
+
+    const inputShape = x.tensor.shape
+    const outputShape = [
+      inputShape[0] * this.size[0],
+      inputShape[1] * this.size[1],
+      inputShape[2]
+    ]
+    let y = new Tensor([], outputShape)
+    for (let i = 0; i < this.size[0]; i++) {
+      for (let j = 0; j < this.size[1]; j++) {
+        ops.assign(
+          y.tensor.lo(i, j, 0).step(this.size[0], this.size[1], 1),
+          x.tensor
+        )
+      }
+    }
+    x.tensor = y.tensor
+
+    // convert back to th ordering if necessary
+    if (this.dimOrdering === 'th') {
+      x.tensor = x.tensor.transpose(2, 0, 1)
+    }
+
+    return x
+  }
+}