From 0560733c2e4492db5ae0af2553e7fd7b6d883007 Mon Sep 17 00:00:00 2001
From: dangqingqing <dangqingqing@baidu.com>
Date: Wed, 2 Aug 2017 18:16:17 +0800
Subject: [PATCH] Add sigmoid backward implenmention.

---
 paddle/operators/sigmoid_op.cc                | 12 ++++++++----
 paddle/operators/sigmoid_op.cu                |  1 +
 paddle/operators/sigmoid_op.h                 | 19 +++++++++++++++++++
 .../v2/framework/tests/test_sigmoid_op.py     | 11 +++++++++++
 4 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/paddle/operators/sigmoid_op.cc b/paddle/operators/sigmoid_op.cc
index a81ab262cc..9e565bb23f 100644
--- a/paddle/operators/sigmoid_op.cc
+++ b/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>);
diff --git a/paddle/operators/sigmoid_op.cu b/paddle/operators/sigmoid_op.cu
index f679b20418..f83483131c 100644
--- a/paddle/operators/sigmoid_op.cu
+++ b/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>);
diff --git a/paddle/operators/sigmoid_op.h b/paddle/operators/sigmoid_op.h
index 3dd23a9ebc..2ea75b4885 100644
--- a/paddle/operators/sigmoid_op.h
+++ b/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
diff --git a/python/paddle/v2/framework/tests/test_sigmoid_op.py b/python/paddle/v2/framework/tests/test_sigmoid_op.py
index 50044a122f..4b0acd3294 100644
--- a/python/paddle/v2/framework/tests/test_sigmoid_op.py
+++ b/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()
-- 
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