Swish activation operator (#6358)

Author: abhinavarora

paddle/operators/activation_op.cc

@@ -506,6 +506,22 @@ It is recommended to use the defaults for this activation.
   }
 };
 
+class SwishOpMaker : public framework::OpProtoAndCheckerMaker {
+ public:
+  SwishOpMaker(framework::OpProto *proto, framework::OpAttrChecker *op_checker)
+      : OpProtoAndCheckerMaker(proto, op_checker) {
+    AddInput("X", "Input of Swish operator");
+    AddOutput("Y", "Output of Swish operator");
+    AddAttr<float>("beta", "Constant beta of swish operator").SetDefault(1.0f);
+    AddComment(R"DOC(
+Swish Activation Operator.
+
+$$y = \frac{x}{1 + e^{- \beta x}}$$
+
+)DOC");
+  }
+};
+
 }  // namespace operators
 }  // namespace paddle
 
@@ -592,6 +608,9 @@ REGISTER_OP(thresholded_relu, ops::ActivationOp, ops::ThresholdedReluOpMaker,
 REGISTER_OP(hard_sigmoid, ops::ActivationOp, ops::HardSigmoidOpMaker,
             hard_sigmoid_grad, ops::ActivationOpGrad);
 
+REGISTER_OP(swish, ops::ActivationOp, ops::SwishOpMaker, swish_grad,
+            ops::ActivationOpGrad);
+
 #define REGISTER_ACTIVATION_CPU_KERNEL(act_type, functor, grad_functor)       \
   REGISTER_OP_CPU_KERNEL(                                                     \
       act_type,                                                               \

paddle/operators/activation_op.h

@@ -700,6 +700,35 @@ struct HardSigmoidGradFunctor : public BaseActivationFunctor<T> {
   }
 };
 
+template <typename T>
+struct SwishFunctor : public BaseActivationFunctor<T> {
+  float beta;
+  typename BaseActivationFunctor<T>::AttrPair GetAttrs() {
+    return {{"beta", &beta}};
+  }
+
+  template <typename Device, typename X, typename Y>
+  void operator()(Device d, X x, Y y) const {
+    y.device(d) = x / (static_cast<T>(1) + (static_cast<T>(-beta) * x).exp());
+  }
+};
+
+template <typename T>
+struct SwishGradFunctor : public BaseActivationFunctor<T> {
+  float beta;
+  typename BaseActivationFunctor<T>::AttrPair GetAttrs() {
+    return {{"beta", &beta}};
+  }
+
+  template <typename Device, typename X, typename Y, typename dY, typename dX>
+  void operator()(Device d, X x, Y y, dY dy, dX dx) const {
+    auto temp1 = static_cast<T>(1) /
+                 (static_cast<T>(1) + (static_cast<T>(-beta) * x).exp());
+    auto temp2 = temp1 * (static_cast<T>(1) - (beta * y));
+    dx.device(d) = dy * ((beta * y) + temp2);
+  }
+};
+
 }  // namespace operators
 }  // namespace paddle
 
@@ -730,4 +759,5 @@ struct HardSigmoidGradFunctor : public BaseActivationFunctor<T> {
   __macro(elu, ELUFunctor, ELUGradFunctor);                          \
   __macro(hard_shrink, HardShrinkFunctor, HardShrinkGradFunctor);    \
   __macro(hard_sigmoid, HardSigmoidFunctor, HardSigmoidGradFunctor); \
+  __macro(swish, SwishFunctor, SwishGradFunctor);                    \
   __macro(thresholded_relu, ThresholdedReluFunctor, ThresholdedReluGradFunctor);

python/paddle/v2/fluid/tests/test_activation_op.py

@@ -1,6 +1,7 @@
 import unittest
 import numpy as np
 from op_test import OpTest
+from scipy.special import expit
 
 
 class TestExp(OpTest):
@@ -455,5 +456,20 @@ def test_check_grad(self):
         self.check_grad(['X'], 'Y', max_relative_error=0.002)
 
 
+class TestSwish(OpTest):
+    def setUp(self):
+        self.op_type = "swish"
+        X = np.random.uniform(0.1, 1, [11, 17]).astype("float32")
+        self.inputs = {'X': X}
+        self.attrs = {'beta': 2.3}
+        self.outputs = {'Y': X * expit(self.attrs['beta'] * X)}
+
+    def test_check_output(self):
+        self.check_output()
+
+    def test_check_grad(self):
+        self.check_grad(['X'], 'Y', max_relative_error=0.008)
+
+
 if __name__ == "__main__":
     unittest.main()