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#ifndef GammaFunctionGenerator_H
#define GammaFunctionGenerator_H
/**
* This class provides a gamma function generator (a<12)
* The threshold works correctly only for integer values of the shape parameter (alpha)
* \author Florian Beaudette
* $Date: 28 Jan 2005 19:30 */
// FAMOS headers
#include "FastSimulation/Utilities/interface/GammaNumericalGenerator.h"
// CLHEP
#include "CLHEP/GenericFunctions/IncompleteGamma.hh"
//STL
#include <vector>
class RandomEngineAndDistribution;
class GammaFunctionGenerator {
public:
/// Constructor
GammaFunctionGenerator();
/// Destructor
virtual ~GammaFunctionGenerator();
/// shoot along a gamma distribution with shape parameter alpha and scale beta
/// values > xmin
double shoot(RandomEngineAndDistribution const*) const;
/// The parameters must be set before shooting
void setParameters(double a, double b, double xm);
private:
/// values 0<a<1.
double gammaFrac(RandomEngineAndDistribution const*) const;
/// integer values
double gammaInt(RandomEngineAndDistribution const*) const;
private:
// The integer numerical functions
std::vector<GammaNumericalGenerator> theGammas;
// The gamma distribution core coefficients
std::vector<double> coreCoeff;
// The gamma distribution core proba
double coreProba;
// possibility to store different limits
std::vector<double> approxLimit;
// boundaries
double xmin;
double xmax;
// closest lower integer
unsigned na;
// alpha-na
double frac;
// alpha function parameters
double alpha, beta;
// Incomlete Gamma = Int(0,x)[t^(alpha-1)exp(-t)dt]/Gamma(alpha);
Genfun::IncompleteGamma myIncompleteGamma;
// some useful integrals
std::vector<double> integralToApproxLimit;
// if xmin>xmax
bool badRange;
};
#endif
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