Adding Nesterov Momentum (#4948)

paddle/operators/momentum_op.cc

@@ -75,12 +75,17 @@ class MomentumOpMaker : public framework::OpProtoAndCheckerMaker {
     AddOutput("VelocityOut", "(Tensor) Output updated velocity");
 
     AddAttr<float>("mu", "(float) Momentum coefficient");
+    AddAttr<bool>("useNesterov", "(bool) Use Nesterov Momentum")
+        .SetDefault(false);
     AddComment(R"DOC(
 
-Momentum Algorithm (momentum).
+Momentum Algorithm with a flag for Nestrov Moemntum (momentum).
 
 velocity = mu * velocity + gradient
-param = param - learning_rate * velocity
+if (use_nesterov):
+  param = param - gradient * learning_rate + mu * velocity * learning_rate
+else:
+  param = param - learning_rate * velocity
 
 )DOC");
   }

paddle/operators/momentum_op.h

@@ -34,6 +34,7 @@ class MomentumOpKernel : public framework::OpKernel<T> {
     velocity_out->mutable_data<T>(ctx.GetPlace());
 
     float mu = ctx.Attr<float>("mu");
+    bool use_nesterov = ctx.Attr<bool>("useNesterov");
 
     auto p_out = framework::EigenVector<T>::Flatten(*param_out);
     auto v_out = framework::EigenVector<T>::Flatten(*velocity_out);
@@ -46,9 +47,15 @@ class MomentumOpKernel : public framework::OpKernel<T> {
     auto place = ctx.GetEigenDevice<Place>();
 
     Eigen::DSizes<int, 1> grad_dsize(grad->numel());
+
     v_out.device(place) = v * mu + g;
+    if (use_nesterov) {
+      p_out.device(place) = p - g * lr.broadcast(grad_dsize) +
+                            v_out * mu * lr.broadcast(grad_dsize);
+    } else {
       p_out.device(place) = p - lr.broadcast(grad_dsize) * v_out;
     }
+  }
 };
 
 }  // namespace operators

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

@@ -3,7 +3,7 @@ import numpy as np
 from op_test import OpTest
 
 
-class TestMomentumOp(OpTest):
+class TestMomentumOp1(OpTest):
     def setUp(self):
         self.op_type = "momentum"
 
@@ -12,6 +12,7 @@ class TestMomentumOp(OpTest):
         velocity = np.zeros((123, 321)).astype("float32")
         learning_rate = np.array([0.001]).astype("float32")
         mu = 0.0001
+        use_nesterov = False
 
         self.inputs = {
             'Param': param,
@@ -23,6 +24,46 @@ class TestMomentumOp(OpTest):
         self.attrs = {'mu': mu}
 
         velocity_out = mu * velocity + grad
+        if use_nesterov:
+            param_out = param - grad * learning_rate + \
+                        velocity_out * mu * learning_rate
+        else:
+            param_out = param - learning_rate * velocity_out
+
+        self.outputs = {'ParamOut': param_out, 'VelocityOut': velocity_out}
+
+    def test_check_output(self):
+        self.check_output()
+
+
+class TestMomentumOp2(OpTest):
+    '''Test Momentum with defaukt values for attributes
+    '''
+
+    def setUp(self):
+        self.op_type = "momentum"
+
+        param = np.random.random((123, 321)).astype("float32")
+        grad = np.random.random((123, 321)).astype("float32")
+        velocity = np.zeros((123, 321)).astype("float32")
+        learning_rate = np.array([0.001]).astype("float32")
+        mu = 0.0001
+        use_nesterov = True
+
+        self.inputs = {
+            'Param': param,
+            'Grad': grad,
+            'Velocity': velocity,
+            'LearningRate': learning_rate
+        }
+
+        self.attrs = {'mu': mu, 'useNesterov': use_nesterov}
+
+        velocity_out = mu * velocity + grad
+        if use_nesterov:
+            param_out = param - grad * learning_rate + \
+                        velocity_out * mu * learning_rate
+        else:
             param_out = param - learning_rate * velocity_out
 
         self.outputs = {'ParamOut': param_out, 'VelocityOut': velocity_out}

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

@@ -46,7 +46,7 @@ class TestRmspropOp1(OpTest):
 
 
 class TestRmspropOp2(OpTest):
-    '''Test RMSProp with defaukt values for attributes
+    '''Test RMSProp with default values for attributes
     '''
 
     def setUp(self):