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