SigmoidFunction.hh

#ifndef GRAIL_SIGMOID_FUNCTION_H
#define GRAIL_SIGMOID_FUNCTION_H
 
#include "Curve.hh"
#include <cmath>
 
namespace grail
{
    namespace curves
    {
        template <typename ContextType>
        class SigmoidFunction final : public Curve<ContextType>
        {
        public:
            SigmoidFunction(std::shared_ptr<utility::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; }
 
            EvaluatorType GetEvaluatorType() const override final { return 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