add tanh and sqrt activation operators

paddle/operators/activation_op.h

@@ -99,5 +99,36 @@ struct ReluGradFunctor {
   }
 };
 
+struct TanhFunctor {
+  template <typename Device, typename X, typename Y>
+  void operator()(Device d, X x, Y y) {
+    y.device(d) = x.tanh();
+  }
+};
+
+template <typename T>
+struct TanhGradFunctor {
+  template <typename Device, typename X, typename Y, typename dY, typename dX>
+  void operator()(Device d, X x, Y y, dY dy, dX dx) {
+    dx.device(d) = dy * (T(1) - y * y);
+  }
+};
+
+struct SqrtFunctor {
+  template <typename Device, typename X, typename Y>
+  void operator()(Device d, X x, Y y) {
+    y.device(d) = x.sqrt();
+  }
+};
+
+template <typename T>
+struct SqrtGradFunctor {
+  template <typename Device, typename X, typename Y, typename dY, typename dX>
+  void operator()(Device d, X x, Y y, dY dy, dX dx) {
+    const T y_conj = Eigen::numext::conj(y);
+    dx.device(d) = static_cast<T>(0.5) * dy / y_conj;
+  }
+};
+
 }  // namespace operators
 }  // namespace paddle