softsign_function.hpp

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#ifndef MLPACK_METHODS_ANN_ACTIVATION_FUNCTIONS_SOFTSIGN_FUNCTION_HPP
#define MLPACK_METHODS_ANN_ACTIVATION_FUNCTIONS_SOFTSIGN_FUNCTION_HPP

#include <mlpack/prereqs.hpp>

namespace mlpack {
namespace ann  {

class SoftsignFunction
{
 public:
  static double Fn(const double x)
  {
    if (x < DBL_MAX)
      return x > -DBL_MAX ? x / (1.0 + std::abs(x)) : -1.0;
    return 1.0;
  }

  template<typename InputVecType, typename OutputVecType>
  static void Fn(const InputVecType& x, OutputVecType& y)
  {
    y.set_size(arma::size(x));

    for (size_t i = 0; i < x.n_elem; ++i)
      y(i) = Fn(x(i));
  }

  static double Deriv(const double y)
  {
    return std::pow(1.0 - std::abs(y), 2);
  }

  template<typename InputVecType, typename OutputVecType>
  static void Deriv(const InputVecType& y, OutputVecType& x)
  {
    x = arma::pow(1.0 - arma::abs(y), 2);
  }

  static double Inv(const double y)
  {
    if (y > 0)
      return y < 1 ? -y / (y - 1) : DBL_MAX;
    else
      return y > -1 ? y / (1 + y) : -DBL_MAX;
  }

  template<typename InputVecType, typename OutputVecType>
  static void Inv(const InputVecType& y, OutputVecType& x)
  {
    x.set_size(arma::size(y));

    for (size_t i = 0; i < y.n_elem; ++i)
      x(i) = Inv(y(i));
  }
}; // class SoftsignFunction

} // namespace ann
} // namespace mlpack

#endif