hard_sigmoid_function.hpp

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#ifndef MLPACK_METHODS_ANN_ACTIVATION_FUNCTIONS_HARD_SIGMOID_FUNCTION_HPP
#define MLPACK_METHODS_ANN_ACTIVATION_FUNCTIONS_HARD_SIGMOID_FUNCTION_HPP

#include <mlpack/prereqs.hpp>
#include <algorithm>

namespace mlpack {
namespace ann  {

class HardSigmoidFunction
{
 public:
  static double Fn(const double x)
  {
    return std::min(1.0, std::max(0.0, 0.2 * x + 0.5));
  }

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

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

  static double Deriv(const double y)
  {
    if (y == 0.0 || y == 1.0)
    {
      return 0.0;
    }
    return 0.2;
  }

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

    for (size_t i = 0; i < y.n_elem; ++i)
    {
      x(i) = Deriv(y(i));
    }
  }
}; // class HardSigmoidFunction

} // namespace ann
} // namespace mlpack

#endif