Identity operator and its gradient

paddle/framework/CMakeLists.txt

@@ -55,5 +55,6 @@ cc_library(paddle_pybind SHARED
     recurrent_op
     uniform_random_op
     gaussian_random_op
-    fill_zeros_like_op)
+    fill_zeros_like_op
+    identity_op)
 endif(WITH_PYTHON)

paddle/framework/pybind.cc

@@ -42,6 +42,7 @@ USE_OP(fill_zeros_like);
 USE_OP_ITSELF(recurrent_op);
 USE_OP(gaussian_random);
 USE_OP(uniform_random);
+USE_OP(identity);
 
 namespace paddle {
 namespace framework {

paddle/operators/CMakeLists.txt

@@ -68,3 +68,4 @@ op_library(recurrent_op SRCS recurrent_op.cc rnn/recurrent_op_utils.cc
     DEPS framework_proto tensor op_registry operator net_op)
 op_library(uniform_random_op
         SRCS uniform_random_op.cc uniform_random_op.cu)
+op_library(identity_op SRCS identity_op.cc identity_op.cu DEPS net_op)

paddle/operators/identity_op.cc

@@ -0,0 +1,71 @@
+/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License. */
+
+#include "paddle/operators/identity_op.h"
+#include "paddle/operators/net_op.h"
+
+namespace paddle {
+namespace operators {
+
+class IdentityOp : public framework::OperatorWithKernel {
+ public:
+  IdentityOp(const std::string &type, const VarNameMap &inputs,
+             const VarNameMap &outputs, const framework::AttributeMap &attrs)
+      : OperatorWithKernel(type, inputs, outputs, attrs) {}
+
+ protected:
+  void InferShape(const framework::InferShapeContext &ctx) const override {
+    auto *in = ctx.Input<framework::Tensor>("X");
+    auto *out = ctx.Output<framework::Tensor>("Out");
+    out->Resize(in->dims());
+  }
+};
+
+class IdentityOpMaker : public framework::OpProtoAndCheckerMaker {
+ public:
+  IdentityOpMaker(framework::OpProto *proto,
+                  framework::OpAttrChecker *op_checker)
+      : OpProtoAndCheckerMaker(proto, op_checker) {
+    AddInput("X", "The input tensor of identity operator.").NotInGradient();
+    AddOutput("Out", "The output tensor of identity operator.").NotInGradient();
+    AddComment(R"DOC(Identity operator
+
+The equation is: Out = X
+)DOC");
+  }
+};
+
+// Identity Op's gradient is identity op, too.
+// Grad(Out=identity_op(X)) => Grad(X) = identity_op(Grad(Out))
+class IdentityGradOp : public NetOp {
+ public:
+  IdentityGradOp(const std::string &type, const VarNameMap &inputs,
+                 const VarNameMap &outputs,
+                 const framework::AttributeMap &attrs)
+      : NetOp(type, inputs, outputs, attrs) {
+    AddOp(framework::OpRegistry::CreateOp(
+        "identity", {{"X", {Input(framework::GradVarName("Out"))}}},
+        {{"Out", {Output(framework::GradVarName("X"))}}}, {}));
+    CompleteAddOp(false);
+  }
+};
+
+}  // namespace operators
+}  // namespace paddle
+
+namespace ops = paddle::operators;
+
+REGISTER_OP(identity, ops::IdentityOp, ops::IdentityOpMaker, identity_grad,
+            ops::IdentityGradOp);
+REGISTER_OP_CPU_KERNEL(identity, ops::IdentityKernel<float>);

paddle/operators/identity_op.cu

@@ -0,0 +1,17 @@
+/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License. */
+
+#include "paddle/operators/identity_op.h"
+
+REGISTER_OP_GPU_KERNEL(identity, paddle::operators::IdentityKernel<float>);

paddle/operators/identity_op.h

@@ -0,0 +1,32 @@
+/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License. */
+
+#pragma once
+
+#include "paddle/framework/op_registry.h"
+#include "paddle/memory/memcpy.h"
+namespace paddle {
+namespace operators {
+template <typename T>
+class IdentityKernel : public framework::OpKernel {
+ public:
+  virtual void Compute(const framework::ExecutionContext& context) const {
+    auto* tensor = context.Output<framework::Tensor>("Out");
+    auto* in = context.Input<framework::Tensor>("X");
+    tensor->CopyFrom<T>(*in, in->place());
+  }
+};
+
+}  // namespace operators
+}  // namespace paddle

python/paddle/v2/framework/tests/CMakeLists.txt

@@ -27,3 +27,4 @@ py_test(test_uniform_random_op SRCS test_uniform_random_op.py)
 py_test(test_recurrent_op SRCS test_recurrent_op.py)
 py_test(test_sgd_op SRCS test_sgd_op.py)
 py_test(test_gradient_checker SRCS test_gradient_checker.py)
+py_test(test_identity_op SRCS test_identity_op.py)

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

@@ -0,0 +1,24 @@
+import unittest
+from op_test_util import OpTestMeta
+from gradient_checker import GradientChecker, create_op
+import numpy as np
+
+
+class IdentityTest(unittest.TestCase):
+    __metaclass__ = OpTestMeta
+
+    def setUp(self):
+        self.type = "identity"
+        self.inputs = {'X': np.random.random((32, 784)).astype("float32")}
+        self.outputs = {'Out': self.inputs['X']}
+
+
+class IdentityGradOpTest(GradientChecker):
+    def test_normal(self):
+        op = create_op("identity")
+        inputs = {"X": np.random.random((10, 10)).astype("float32")}
+        self.check_grad(op, inputs, set("X"), "Out")
+
+
+if __name__ == '__main__':
+    unittest.main()