elish_function.hpp

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#ifndef MLPACK_METHODS_ANN_ACTIVATION_FUNCTIONS_ELISH_FUNCTION_HPP
#define MLPACK_METHODS_ANN_ACTIVATION_FUNCTIONS_ELISH_FUNCTION_HPP

#include <mlpack/prereqs.hpp>

namespace mlpack {
namespace ann  {

class ElishFunction
{
 public:
  static double Fn(const double x)
  {
    if (x < 0.0)
      return (std::exp(x) - 1) / (1 + std::exp(-x));

    return x / (1 + std::exp(-x));
  }

  template<typename InputVecType, typename OutputVecType>
  static void Fn(const InputVecType& x, OutputVecType& y)
  {
    y = ((x < 0.0) % ((arma::exp(x) -1) / (1 + arma::exp(-x))))
        + ((x >= 0.0) % (x / (1 + arma::exp(-x))));
  }

  static double Deriv(const double y)
  {
    if (y < 0.0)
    {
      return std::exp(y) - 2 / (1 + std::exp(y)) +
          2 / std::pow(1 + std::exp(y) , 2);
    }

    return 1 / (1 + std::exp(-y)) + y * std::exp(-y) /
        std::pow(1 + std::exp(-y) , 2);
  }

  template<typename InputVecType, typename OutputVecType>
  static void Deriv(const InputVecType& y, OutputVecType& x)
  {
    x = ((y < 0.0) % (arma::exp(y) - 2 / (1 + arma::exp(y)) + 2 / arma::pow(
        1 + arma::exp(y), 2))) + ((y >= 0.0) % (1 / (1 + arma::exp(-y)) + y %
        arma::exp(-y) / arma::pow(1 + arma::exp(-y), 2)));
  }
}; // class ElishFunction

} // namespace ann
} // namespace mlpack

#endif