ActivationFunction.h

/* Copyright (c) 2016 Baidu, Inc. 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 <string>

namespace paddle {
struct Argument;
class ActivationFunction {
public:
  static ActivationFunction* create(const std::string& type);

  ActivationFunction() {}

  virtual ~ActivationFunction() {}

  // act.value <- f(act.value),
  // where f is the activation function.
  // Suppose that before calling forward(), act.value is x and
  // after forward() is called, act.value is y, then y = f(x),
  // Usually, act is Layer::output_
  virtual void forward(Argument& act) = 0;

  // x and y are defined in the above comment for forward().
  // Before calling backward(), act.grad = dE / dy, where E is the error/cost.
  // After backward() returns, act.grad = dE / dx = (dE/dy) * (dy/dx)
  virtual void backward(Argument& act) = 0;

  virtual const std::string& getName() const = 0;
};

}  // namespace paddle