SigmoidFunction.hh

// Copyright QED Software 2023.
 
#ifndef GRAIL_SIGMOID_FUNCTION_H
#define GRAIL_SIGMOID_FUNCTION_H
 
#include <cmath>
#include "Curve.hh"
 
namespace grail
{
namespace evaluator
{
 template <typename ContextType>
 class SigmoidFunction final : public Curve<ContextType>
 {
 public:
 SigmoidFunction(std::shared_ptr<Evaluator<ContextType>> childEvaluator,
 float range,
 float slope,
 float threshold,
 float displacement)
 : Curve<ContextType>{childEvaluator},
 range(range),
 slope(slope),
 threshold(threshold),
 displacement(displacement)
 {
 }
 
 virtual float Sample(float argument) const override final
 {
 float x = slope * (argument - threshold);
 if(x < 0)
 {
 float exp_x = std::exp(x);
 return ((range * exp_x) / (1 + exp_x)) + displacement;
 }
 else
 {
 return (range / (1 + std::exp(-x))) + displacement;
 }
 }
 
 float GetRange() const { return range; }
 float GetSlope() const { return slope; }
 float GetThreshold() const { return threshold; }
 float GetDisplacement() const { return displacement; }
 
 virtual data::EvaluatorType GetEvaluatorType() const override final { return data::EvaluatorType::CURVE_SIGMOID; }
 
 private:
 float range = 0.0f;
 float slope = 0.0f;
 float threshold = 0.0f;
 float displacement = 0.0f;
 };
}
}
 
#endif // GRAIL_SIGMOID_FUNCTION_H