softplus_function.hpp

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#ifndef MLPACK_METHODS_ANN_ACTIVATION_FUNCTIONS_SOFTPLUS_FUNCTION_HPP
#define MLPACK_METHODS_ANN_ACTIVATION_FUNCTIONS_SOFTPLUS_FUNCTION_HPP

#include <mlpack/prereqs.hpp>

namespace mlpack {
namespace ann  {

class SoftplusFunction
{
 public:
  static double Fn(const double x)
  {
    const double val = std::log(1 + std::exp(x));
    if (std::isfinite(val))
      return val;
    return x;
  }

  template<typename InputType, typename OutputType>
  static void Fn(const InputType& x, OutputType& 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 1.0 / (1 + std::exp(-y));
  }

  template<typename InputType, typename OutputType>
  static void Deriv(const InputType& y, OutputType& x)
  {
    x = 1.0 / (1 + arma::exp(-y));
  }

  static double Inv(const double y)
  {
    const double val = std::log(std::exp(y) - 1);
    if (std::isfinite(val))
      return val;
    return y;
  }

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

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

} // namespace ann
} // namespace mlpack

#endif