animaKummerFunctions.h

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#pragma once

#include "AnimaSpecialFunctionsExport.h"
#include <cmath>

namespace anima
{

ANIMASPECIALFUNCTIONS_EXPORT
double PochHammer(const double &x,
                  const unsigned int n);

ANIMASPECIALFUNCTIONS_EXPORT
double
KummerMethod1(const double &x, const double &a, const double &b,
              const unsigned int maxIter = 1000, const double tol = 1.0e-8);

ANIMASPECIALFUNCTIONS_EXPORT
double
KummerMethod2(const double &x, const double &a, const double &b,
              const unsigned int maxIter = 1000, const double tol = 1.0e-8);

ANIMASPECIALFUNCTIONS_EXPORT
double
KummerIntegrandMethod(const double &x, const double &a, const double &b);

ANIMASPECIALFUNCTIONS_EXPORT
double
GetKummerFunctionValue(const double &x, const double &a, const double &b,
                       const unsigned int maxIter = 1000, const double tol = 1.0e-8);

ANIMASPECIALFUNCTIONS_EXPORT
double
GetScaledKummerFunctionValue(const double &x, const double &a, const double &b,
                             const unsigned int maxIter = 1000, const double tol = 1.0e-8);

class KummerIntegrand
{
public:
    void SetXValue(double val) {m_XValue = val;}
    void SetAValue(double val) {m_AValue = val;}
    void SetBValue(double val) {m_BValue = val;}
    
    double operator() (const double t)
    {
        // For better numerical stability
        double tModified = t - (m_XValue > 0.0);
        return std::exp(m_XValue * tModified) * std::pow(t, m_AValue - 1.0) * std::pow(1.0 - t, m_BValue - m_AValue - 1.0);
    }
    
private:
    double m_XValue, m_AValue, m_BValue;
};

} // end namespace anima