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)
  {
    if (x < DBL_MAX)
      return x > -DBL_MAX ? std::log(1 + std::exp(x)) : 0;
    return 1.0;
  }

  template<typename InputVecType, typename OutputVecType>
  static void fn(const InputVecType& x, OutputVecType& y)
  {
    y = 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 InputVecType, typename OutputVecType>
  static void deriv(const InputVecType& y, OutputVecType& x)
  {
    x = 1.0 / (1 + arma::exp(-y));
  }

  static double inv(const double y)
  {
    return y > 0 ? arma::trunc_log(arma::trunc_exp(y) - 1) : 0;
  }

  template<typename InputVecType, typename OutputVecType>
  static void inv(const InputVecType& y, OutputVecType& x)
  {
    x = y;

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

} // namespace ann
} // namespace mlpack

#endif