softshrink_impl.hpp

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#ifndef MLPACK_METHODS_ANN_LAYER_SOFTSHRINK_IMPL_HPP
#define MLPACK_METHODS_ANN_LAYER_SOFTSHRINK_IMPL_HPP

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

namespace mlpack {
namespace ann  {

// This constructor is called for Soft Shrink activation function.
// lambda is a hyperparameter.
template<typename InputDataType, typename OutputDataType>
SoftShrink<InputDataType, OutputDataType>::SoftShrink(const double lambda) :
    lambda(lambda)
{
  // Nothing to do here.
}

template<typename InputDataType, typename OutputDataType>
template<typename InputType, typename OutputType>
void SoftShrink<InputDataType, OutputDataType>::Forward(
    const InputType& input, OutputType& output)
{
  output = (input > lambda) % (input - lambda) + (
    input < -lambda) % (input + lambda);
}

template<typename InputDataType, typename OutputDataType>
template<typename DataType>
void SoftShrink<InputDataType, OutputDataType>::Backward(
    const DataType& input, DataType& gy, DataType& g)
{
  DataType derivative;
  derivative = (arma::ones(arma::size(input)) - (input == 0));
  g = gy % derivative;
}

template<typename InputDataType, typename OutputDataType>
template<typename Archive>
void SoftShrink<InputDataType, OutputDataType>::serialize(
    Archive& ar,
    const uint32_t /* version */)
{
  ar(CEREAL_NVP(lambda));
}

} // namespace ann
} // namespace mlpack

#endif