Add variable() to chain API. (#730)

Author: Nikhil Thorat

src/tensor.ts

@@ -879,6 +879,11 @@ export class Tensor<R extends Rank = Rank> {
     return ops.localResponseNormalization(
         this, radius, bias, alpha, beta, normRegion);
   }
+
+  variable(trainable = true, name?: string, dtype?: DataType): Variable<R> {
+    this.throwIfDisposed();
+    return Variable.variable(this, trainable, name, dtype);
+  }
 }
 
 /** @doclink Tensor */

src/variable_test.ts

@@ -30,6 +30,14 @@ describeWithFlags('variable', ALL_ENVS, () => {
     expectArraysClose(v, [4, 5, 6]);
   });
 
+  it('simple chain assign', () => {
+    const v = dl.tensor1d([1, 2, 3]).variable();
+    expectArraysClose(v, [1, 2, 3]);
+
+    v.assign(dl.tensor1d([4, 5, 6]));
+    expectArraysClose(v, [4, 5, 6]);
+  });
+
   it('default names are unique', () => {
     const v = variable(dl.tensor1d([1, 2, 3]));
     expect(v.name).not.toBeNull();
@@ -50,13 +58,19 @@ describeWithFlags('variable', ALL_ENVS, () => {
         .toThrowError();
   });
 
-  it('math ops can take variables', () => {
+  it('ops can take variables', () => {
     const value = dl.tensor1d([1, 2, 3]);
     const v = variable(value);
     const res = dl.sum(v);
     expectArraysClose(res, [6]);
   });
 
+  it('chained variables works', () => {
+    const v = dl.tensor1d([1, 2, 3]).variable();
+    const res = dl.sum(v);
+    expectArraysClose(res, [6]);
+  });
+
   it('variables are not affected by tidy', () => {
     let v: Variable<Rank.R1>;
     expect(dl.memory().numTensors).toBe(0);