Add sigmoid backward implenmention.

paddle/operators/sigmoid_op.cc

@@ -37,10 +37,12 @@ public:
 
 class SigmoidOpGrad : public OperatorWithKernel {
 protected:
-  void InferShape(const InferShapeContext &ctx) const override {}
-  std::string DebugString() const override {
-    LOG(INFO) << "SigmoidGrad";
-    return "";
+  void InferShape(const InferShapeContext &ctx) const override {
+    PADDLE_ENFORCE(ctx.InputSize() == 1,
+                   "Sigmoid Gradient Op only have one input");
+    PADDLE_ENFORCE(ctx.OutputSize() == 1,
+                   "Sigmoid Gradient Op only have one output");
+    ctx.Output<Tensor>(0)->Resize(ctx.Input<Tensor>(0)->dims());
   }
 };
 
@@ -51,3 +53,5 @@ REGISTER_OP(sigmoid, ops::SigmoidOp, ops::SigmoidOpMaker);
 REGISTER_GRADIENT_OP(sigmoid, sigmoid_grad, ops::SigmoidOpGrad);
 
 REGISTER_OP_CPU_KERNEL(sigmoid, ops::SigmoidKernel<ops::CPUPlace, float>);
+REGISTER_OP_CPU_KERNEL(sigmoid_grad,
+                       ops::SigmoidGradKernel<ops::CPUPlace, float>);

paddle/operators/sigmoid_op.cu

@@ -1,3 +1,4 @@
 #include "paddle/operators/sigmoid_op.h"
 
 REGISTER_OP_GPU_KERNEL(sigmoid, ops::SigmoidKernel<ops::GPUPlace, float>);
+REGISTER_OP_GPU_KERNEL(sigmoid_grad, ops::SigmoidGradKernel<ops::GPUPlace, float>);

paddle/operators/sigmoid_op.h

@@ -32,5 +32,24 @@ public:
         1.0 / (1.0 + (-1.0 * EigenVector<T>::Flatten(*input)).exp());
   }
 };
+
+template <typename Place, typename T>
+class SigmoidGradKernel : public OpKernel {
+public:
+  void Compute(const ExecutionContext& context) const override {
+    // TODO(qingqing) maybe a helper funciton is needed fo the name x@GRAD
+    auto y_t = context.Input<Tensor>("Y");
+    auto dy_t = context.Input<Tensor>("Y@GRAD");
+    auto dx_t = context.Output<Tensor>("X@GRAD");
+
+    dx_t->mutable_data<T>(context.GetPlace());
+
+    auto dx = EigenVector<T>::Flatten(*dx_t);
+    auto y = EigenVector<T>::Flatten(*y_t);
+    auto dy = EigenVector<T>::Flatten(*dy_t);
+    dx.device(*(context.GetEigenDevice<Place>())) = dy * y * (1. - y);
+  }
+};
+
 }  // namespace operators
 }  // namespace paddle

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

@@ -12,5 +12,16 @@ class TestSigmoidOp(unittest.TestCase):
         self.Y = 1 / (1 + np.exp(-self.X))
 
 
+#class TestSigmoidGradOp(unittest.TestCase):
+#    __metaclass__ = OpTestMeta
+#
+#    def setUp(self):
+#        self.type = "sigmoid_grad"
+#        self.Y = np.random.random((32, 100)).astype("float32")
+#        self.dY = np.random.random((32, 100)).astype("float32")
+#        self.dX = self.dY * self.Y * (1 - self.Y)
+#        print self.dX
+#
+
 if __name__ == '__main__':
     unittest.main()