base_layer.hpp

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#ifndef MLPACK_METHODS_ANN_LAYER_BASE_LAYER_HPP
#define MLPACK_METHODS_ANN_LAYER_BASE_LAYER_HPP

#include <mlpack/prereqs.hpp>
#include <mlpack/methods/ann/activation_functions/logistic_function.hpp>
#include <mlpack/methods/ann/activation_functions/identity_function.hpp>
#include <mlpack/methods/ann/activation_functions/rectifier_function.hpp>
#include <mlpack/methods/ann/activation_functions/tanh_function.hpp>
#include <mlpack/methods/ann/activation_functions/softplus_function.hpp>
#include <mlpack/methods/ann/activation_functions/hard_sigmoid_function.hpp>

namespace mlpack {
namespace ann  {

template <
    class ActivationFunction = LogisticFunction,
    typename InputDataType = arma::mat,
    typename OutputDataType = arma::mat
>
class BaseLayer
{
 public:
  BaseLayer()
  {
    // Nothing to do here.
  }

  template<typename InputType, typename OutputType>
  void Forward(const InputType&& input, OutputType&& output)
  {
    ActivationFunction::Fn(input, output);
  }

  template<typename eT>
  void Backward(const arma::Mat<eT>&& input,
                arma::Mat<eT>&& gy,
                arma::Mat<eT>&& g)
  {
    arma::Mat<eT> derivative;
    ActivationFunction::Deriv(input, derivative);
    g = gy % derivative;
  }

  OutputDataType const& OutputParameter() const { return outputParameter; }
  OutputDataType& OutputParameter() { return outputParameter; }

  OutputDataType const& Delta() const { return delta; }
  OutputDataType& Delta() { return delta; }

  template<typename Archive>
  void serialize(Archive& /* ar */, const unsigned int /* version */)
  {
    /* Nothing to do here */
  }

 private:
  OutputDataType delta;

  OutputDataType outputParameter;
}; // class BaseLayer

// Convenience typedefs.

template <
    class ActivationFunction = LogisticFunction,
    typename InputDataType = arma::mat,
    typename OutputDataType = arma::mat
>
using SigmoidLayer = BaseLayer<
    ActivationFunction, InputDataType, OutputDataType>;

template <
    class ActivationFunction = IdentityFunction,
    typename InputDataType = arma::mat,
    typename OutputDataType = arma::mat
>
using IdentityLayer = BaseLayer<
    ActivationFunction, InputDataType, OutputDataType>;

template <
    class ActivationFunction = RectifierFunction,
    typename InputDataType = arma::mat,
    typename OutputDataType = arma::mat
>
using ReLULayer = BaseLayer<
    ActivationFunction, InputDataType, OutputDataType>;

template <
    class ActivationFunction = TanhFunction,
    typename InputDataType = arma::mat,
    typename OutputDataType = arma::mat
>
using TanHLayer = BaseLayer<
    ActivationFunction, InputDataType, OutputDataType>;

template <
    class ActivationFunction = SoftplusFunction,
    typename InputDataType = arma::mat,
    typename OutputDataType = arma::mat
>
using SoftPlusLayer = BaseLayer<
    ActivationFunction, InputDataType, OutputDataType>;

template <
    class ActivationFunction = HardSigmoidFunction,
    typename InputDataType = arma::mat,
    typename OutputDataType = arma::mat
>
using HardSigmoidLayer = BaseLayer<
    ActivationFunction, InputDataType, OutputDataType>;

} // namespace ann
} // namespace mlpack

#endif