Adding the interface for the momentum optimizer (#4919)

* Adding the interface for the momentum optimizer
* Adding a comment about accumulators

python/paddle/v2/framework/tests/test_optimizer.py

@@ -6,7 +6,7 @@ import paddle.v2.framework.optimizer as optimizer
 
 class TestOptimizer(unittest.TestCase):
     def test_sgd_optimizer(self):
-        program = framework.g_program
+        program = framework.Program()
         block = program.global_block()
         mul_x = block.create_parameter(
             dtype="float32", shape=[5, 10], lod_level=0, name="mul.x")
@@ -14,7 +14,7 @@ class TestOptimizer(unittest.TestCase):
             dtype="float32", shape=[10, 8], lod_level=0, name="mul.y")
         mul_out = block.create_var(
             dtype="float32", shape=[5, 8], lod_level=0, name="mul.out")
-        mul_op = block.append_op(
+        block.append_op(
             type="mul",
             inputs={"X": mul_x,
                     "Y": mul_y},
@@ -27,5 +27,47 @@ class TestOptimizer(unittest.TestCase):
         self.assertEqual(sgd_op.type, "sgd")
 
 
+class TestMomentumOptimizer(unittest.TestCase):
+    class MockMomentum(optimizer.MomentumOptimizer):
+        def get_accumulators(self):
+            return self._accumulators
+
+        def get_velocity_str(self):
+            return self._velocity_acc_str
+
+    def test_momentum_optimizer(self):
+        program = framework.Program()
+        block = program.global_block()
+        mul_x = block.create_parameter(
+            dtype="float32", shape=[5, 10], lod_level=0, name="mul.x")
+        mul_y = block.create_var(
+            dtype="float32", shape=[10, 8], lod_level=0, name="mul.y")
+        mul_out = block.create_var(
+            dtype="float32", shape=[5, 8], lod_level=0, name="mul.out")
+        block.append_op(
+            type="mul",
+            inputs={"X": mul_x,
+                    "Y": mul_y},
+            outputs={"Out": mul_out},
+            attrs={"x_num_col_dims": 1})
+        momentum_optimizer = self.MockMomentum(learning_rate=0.01, momentum=0.2)
+        params_grads = momentum_optimizer.create_backward_pass(mul_out)
+        self.assertEqual(len(params_grads), 1)
+        self.assertEqual(len(momentum_optimizer.get_accumulators()), 0)
+        opts = momentum_optimizer.create_optimization_pass(params_grads,
+                                                           mul_out)
+        self.assertEqual(len(opts), 1)
+        sgd_op = opts[0]
+        self.assertEqual(sgd_op.type, "momentum")
+
+        # Check accumulators
+        accumulators = momentum_optimizer.get_accumulators()
+        self.assertEqual(len(accumulators), 1)
+        self.assertTrue(momentum_optimizer.get_velocity_str() in accumulators)
+        velocity_acc = accumulators[momentum_optimizer.get_velocity_str()]
+        self.assertEqual(len(velocity_acc), 1)
+        self.assertTrue(mul_x.name in velocity_acc)
+
+
 if __name__ == '__main__':
     unittest.main()