added support prod reduce op (#1279)

* added support prod reduce op

* addressed the review comments, and removed the gradient func for prod op, since it requires the cumprod op

src/kernels/backend.ts

@@ -108,6 +108,7 @@ export interface KernelBackend extends TensorStorage, BackendTimer {
   floorDiv(a: Tensor, b: Tensor): Tensor;
 
   sum(x: Tensor, axes: number[]): Tensor;
+  prod(x: Tensor, axes: number[]): Tensor;
 
   unsortedSegmentSum<T extends Tensor>(
       x: T, segmentIds: Tensor1D, numSegments: number): Tensor;

src/kernels/backend_cpu.ts

@@ -489,6 +489,28 @@ export class MathBackendCPU implements KernelBackend {
     return result;
   }
 
+  prod(x: Tensor, axes: number[]): Tensor {
+    this.assertNotComplex(x, 'sum');
+
+    const [outShape, reduceShape] =
+        axis_util.computeOutAndReduceShapes(x.shape, axes);
+    const resultDtype = upcastType(x.dtype, 'int32');
+    const result = ops.zeros(outShape, resultDtype);
+    const reduceSize = util.sizeFromShape(reduceShape);
+    const vals = result.dataSync();
+
+    const aVals = x.dataSync();
+    for (let i = 0; i < vals.length; ++i) {
+      const offset = i * reduceSize;
+      let prod = 1;
+      for (let j = 0; j < reduceSize; ++j) {
+        prod *= aVals[offset + j];
+      }
+      vals[i] = prod;
+    }
+    return result;
+  }
+
   unsortedSegmentSum<T extends Tensor>(
       x: T, segmentIds: Tensor1D, numSegments: number): Tensor {
     this.assertNotComplex(x, 'unsortedSegmentSum');

src/kernels/backend_webgl.ts

@@ -769,7 +769,7 @@ export class MathBackendWebGL implements KernelBackend {
   }
 
   private reduce(
-      x: Tensor2D, reduceType: 'all'|'any'|'max'|'min'|'sum',
+      x: Tensor2D, reduceType: 'all'|'any'|'max'|'min'|'sum'|'prod',
       dtype: DataType): Tensor2D {
     const batchSize = x.shape[0];
     const inSize = x.shape[1];
@@ -824,6 +824,15 @@ export class MathBackendWebGL implements KernelBackend {
     return this.reduce(a2D, 'sum', outputDType).reshape(outShape);
   }
 
+  prod(x: Tensor, axes: number[]): Tensor {
+    const [outShape, reduceShape] =
+        axis_util.computeOutAndReduceShapes(x.shape, axes);
+    const inSize = util.sizeFromShape(reduceShape);
+    const a2D = x.as2D(-1, inSize);
+    const outputDType = sumOutType(x.dtype);
+    return this.reduce(a2D, 'prod', outputDType).reshape(outShape);
+  }
+
   unsortedSegmentSum<T extends Tensor>(
       x: T, segmentIds: Tensor1D, numSegments: number): Tensor {
     let axis = 0;

src/kernels/webgl/reduce_gpu.ts

@@ -24,7 +24,8 @@ export class ReduceProgram implements GPGPUProgram {
   userCode: string;
 
   constructor(
-      reduceInfo: ReduceInfo, reduceType: 'all'|'any'|'max'|'min'|'sum') {
+      reduceInfo: ReduceInfo,
+      reduceType: 'all'|'any'|'max'|'min'|'sum'|'prod') {
     const windowSize = reduceInfo.windowSize;
     const batchSize = reduceInfo.batchSize;
     const inSize = reduceInfo.inSize;
@@ -34,7 +35,9 @@ export class ReduceProgram implements GPGPUProgram {
     let initializationValue = '0.0';
     let compareOp = ``;
 
-    if (reduceType === 'min') {
+    if (reduceType === 'prod') {
+      initializationValue = '1.0';
+    } else if (reduceType === 'min') {
       initializationValue = '1.0 / 0.0';
       compareOp = `min`;
     } else if (reduceType === 'max') {
@@ -47,6 +50,8 @@ export class ReduceProgram implements GPGPUProgram {
 
     if (reduceType === 'sum') {
       returnValue = `sumValue`;
+    } else if (reduceType === 'prod') {
+      returnValue = `prodValue`;
     } else if (reduceType === 'all') {
       returnValue = `allValue`;
     } else if (reduceType === 'any') {
@@ -59,6 +64,9 @@ export class ReduceProgram implements GPGPUProgram {
     let updateSnippet = `
       if (${reduceType === 'sum'}) {
         sumValue += dot(values, ones);
+      } else if (${reduceType === 'prod'}) {
+        vec2 tmp = vec2(values[0], values[1]) * vec2(values[2], values[3]);
+        prodValue *= tmp[0] * tmp[1];
       } else {
         minMaxValue = ${compareOp}(values, minMaxValue);
       }
@@ -108,6 +116,7 @@ export class ReduceProgram implements GPGPUProgram {
         int inOffset = outIdx * ${windowSize};
 
         vec4 minMaxValue = vec4(${initializationValue});
+        float prodValue = 1.0;
         float sumValue = 0.0;
         float allValue = 1.0;
         float anyValue = 0.0;

src/ops/reduction_ops.ts

@@ -142,6 +142,60 @@ function sum_<T extends Tensor>(
   return customOp($x) as T;
 }
 
+/**
+ * Computes the product of elements across dimensions of a `Tensor`.
+ *
+ * Reduces the input along the dimensions given in `axes`. Unless `keepDims`
+ * is true, the rank of the `Tensor` is reduced by 1 for each entry in `axes`.
+ * If `keepDims` is true, the reduced dimensions are retained with length 1.
+ * If `axes` has no entries, all dimensions are reduced, and a `Tensor` with a
+ * single element is returned.
+ *
+ * ```js
+ * const x = tf.tensor1d([1, 2, 3]);
+ *
+ * x.prod().print();  // or tf.prod(x)
+ * ```
+ *
+ * ```js
+ * const x = tf.tensor2d([1, 2, 3, 4], [2, 2]);
+ *
+ * const axis = 1;
+ * x.prod(axis).print();  // or tf.prod(x, axis)
+ * ```
+ *
+ * @param x The input tensor to compute the product over. If the dtype is `bool`
+ *   it will be converted to `int32` and the output dtype will be `int32`.
+ * @param axis The dimension(s) to reduce. By default it reduces
+ *     all dimensions.
+ * @param keepDims If true, retains reduced dimensions with size 1.
+ */
+/** @doc {heading: 'Operations', subheading: 'Reduction'} */
+function prod_<T extends Tensor>(
+    x: Tensor|TensorLike, axis: number|number[] = null, keepDims = false): T {
+  let $x = convertToTensor(x, 'x', 'prod');
+
+  if ($x.dtype === 'bool') {
+    $x = $x.toInt();
+  }
+  const axes = axis_util.parseAxisParam(axis, $x.shape);
+
+  const permutation = axis_util.getAxesPermutation(axes, $x.rank);
+  let reductionAxes = axes;
+  let permutedX = $x;
+  if (permutation != null) {
+    permutedX = $x.transpose(permutation);
+    reductionAxes = axis_util.getInnerMostAxes(reductionAxes.length, $x.rank);
+  }
+  let value = ENV.engine.runKernel(
+      backend => backend.prod(permutedX, reductionAxes), {permutedX});
+  if (keepDims) {
+    const newShape = axis_util.expandShapeToKeepDim(value.shape, axes);
+    value = value.reshape(newShape);
+  }
+
+  return value as T;
+}
 /**
  * Computes the mean of elements across dimensions of a `Tensor`.
  *
@@ -554,3 +608,4 @@ export const mean = op({mean_});
 export const min = op({min_});
 export const moments = op({moments_});
 export const sum = op({sum_});
+export const prod = op({prod_});

src/ops/reduction_ops_test.ts

@@ -852,6 +852,105 @@ describeWithFlags('Reduction: sum', ALL_ENVS, () => {
   });
 });
 
+describeWithFlags('Reduction: prod', ALL_ENVS, () => {
+  it('basic', () => {
+    const a = tf.tensor2d([1, 2, 3, 0, 0, 1], [3, 2]);
+    const result = tf.prod(a);
+    expectNumbersClose(result.get(), 0);
+  });
+
+  it('propagates NaNs', () => {
+    const a = tf.tensor2d([1, 2, 3, NaN, 0, 1], [3, 2]);
+    expect(tf.prod(a).get()).toEqual(NaN);
+  });
+
+  it('prod over dtype int32', () => {
+    const a = tf.tensor1d([1, 5, 7, 3], 'int32');
+    const prod = tf.prod(a);
+    expect(prod.get()).toBe(105);
+  });
+
+  it('prod over dtype bool', () => {
+    const a = tf.tensor1d([true, false, false, true, true], 'bool');
+    const prod = tf.prod(a);
+    expect(prod.get()).toBe(0);
+  });
+
+  it('prods all values in 2D array with keep dim', () => {
+    const a = tf.tensor2d([1, 2, 3, 1, 0, 1], [3, 2]);
+    const res = tf.prod(a, null, true /* keepDims */);
+
+    expect(res.shape).toEqual([1, 1]);
+    expectArraysClose(res, [0]);
+  });
+
+  it('prods across axis=0 in 2D array', () => {
+    const a = tf.tensor2d([1, 2, 3, 1, 0, 1], [3, 2]);
+    const res = tf.prod(a, [0]);
+
+    expect(res.shape).toEqual([2]);
+    expectArraysClose(res, [0, 2]);
+  });
+
+  it('prods across axis=0 in 2D array, keepDims', () => {
+    const a = tf.tensor2d([1, 2, 3, 1, 0, 1], [3, 2]);
+    const res = tf.prod(a, [0], true /* keepDims */);
+
+    expect(res.shape).toEqual([1, 2]);
+    expectArraysClose(res, [0, 2]);
+  });
+
+  it('prods across axis=1 in 2D array', () => {
+    const a = tf.tensor2d([1, 2, 3, 1, 1, 1], [3, 2]);
+    const res = tf.prod(a, [1]);
+
+    expect(res.shape).toEqual([3]);
+    expectArraysClose(res, [2, 3, 1]);
+  });
+
+  it('2D, axis=1 provided as number', () => {
+    const a = tf.tensor2d([1, 2, 3, 1, 1, 1], [2, 3]);
+    const res = tf.prod(a, 1);
+
+    expect(res.shape).toEqual([2]);
+    expectArraysClose(res, [6, 1]);
+  });
+
+  it('2D, axis = -1 provided as number', () => {
+    const a = tf.tensor2d([1, 2, 3, 1, 1, 1], [2, 3]);
+    const res = tf.prod(a, -1);
+
+    expect(res.shape).toEqual([2]);
+    expectArraysClose(res, [6, 1]);
+  });
+
+  it('prods across axis=0,1 in 2D array', () => {
+    const a = tf.tensor2d([1, 2, 3, 1, 1, 1], [3, 2]);
+    const res = tf.prod(a, [0, 1]);
+
+    expect(res.shape).toEqual([]);
+    expectArraysClose(res, [6]);
+  });
+
+  it('2D, axis=[-1,-2] in 2D array', () => {
+    const a = tf.tensor2d([1, 2, 3, 1, 1, 1], [3, 2]);
+    const res = tf.prod(a, [-1, -2]);
+
+    expect(res.shape).toEqual([]);
+    expectArraysClose(res, [6]);
+  });
+
+  it('throws when passed a non-tensor', () => {
+    expect(() => tf.prod({} as tf.Tensor))
+        .toThrowError(/Argument 'x' passed to 'prod' must be a Tensor/);
+  });
+
+  it('accepts a tensor-like object', () => {
+    const result = tf.prod([[1, 2], [3, 1], [1, 1]]);
+    expectNumbersClose(result.get(), 6);
+  });
+});
+
 describeWithFlags('Reduction: mean', ALL_ENVS, () => {
   it('basic', () => {
     const a = tf.tensor2d([1, 2, 3, 0, 0, 1], [3, 2]);

src/tensor.ts

@@ -190,6 +190,8 @@ export interface OpHandler {
   logSumExp<T extends Tensor>(
       x: Tensor, axis: number|number[], keepDims: boolean): T;
   sum<T extends Tensor>(x: Tensor, axis: number|number[], keepDims: boolean): T;
+  prod<T extends Tensor>(x: Tensor, axis: number|number[], keepDims: boolean):
+      T;
   mean<T extends Tensor>(x: Tensor, axis: number|number[], keepDims: boolean):
       T;
   min<T extends Tensor>(x: Tensor, axis: number|number[], keepDims: boolean): T;
@@ -769,6 +771,10 @@ export class Tensor<R extends Rank = Rank> {
     this.throwIfDisposed();
     return opHandler.sum(this, axis, keepDims);
   }
+  prod<T extends Tensor>(axis: number|number[] = null, keepDims = false): T {
+    this.throwIfDisposed();
+    return opHandler.prod(this, axis, keepDims);
+  }
   mean<T extends Tensor>(axis: number|number[] = null, keepDims = false): T {
     this.throwIfDisposed();
     return opHandler.mean(this, axis, keepDims);