softmax_impl.hpp

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#ifndef MLPACK_METHODS_ANN_LAYER_SOFTMAX_IMPL_HPP
#define MLPACK_METHODS_ANN_LAYER_SOFTMAX_IMPL_HPP

// In case it hasn't yet been included.
#include "softmax.hpp"

namespace mlpack {
namespace ann  {

template<typename InputDataType, typename OutputDataType>
Softmax<InputDataType, OutputDataType>::Softmax()
{
  // Nothing to do here.
}

template<typename InputDataType, typename OutputDataType>
template<typename InputType, typename OutputType>
void Softmax<InputDataType, OutputDataType>::Forward(
    const InputType& input,
    OutputType& output)
{
  InputType softmaxInput = arma::exp(input.each_row() -
      arma::max(input, 0));
  output = softmaxInput.each_row() / sum(softmaxInput, 0);
}

template<typename InputDataType, typename OutputDataType>
template<typename eT>
void Softmax<InputDataType, OutputDataType>::Backward(
    const arma::Mat<eT>& input,
    const arma::Mat<eT>& gy,
    arma::Mat<eT>& g)
{
  g = input % (gy - arma::repmat(arma::sum(gy % input), input.n_rows, 1));
}

template<typename InputDataType, typename OutputDataType>
template<typename Archive>
void Softmax<InputDataType, OutputDataType>::serialize(
    Archive& /* ar */,
    const uint32_t /* version */)
{
  // Nothing to do here.
}

} // namespace ann
} // namespace mlpack

#endif