RPCChargeGenerator.h

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#ifndef _RPCChargeGenerator_h_
#define _RPCChargeGenerator_h_

#include <vector>
#include <utl/Math.h>
#include <utl/RandomEngine.h>
#include <boost/math/special_functions/gamma.hpp>


namespace CLHEP {
  class RandGeneral;
}

namespace RPCSimulatorLX {


class RPCChargeGenerator {

 public:

  RPCChargeGenerator(double k0, double theta0, double referenceAngle);
  virtual ~RPCChargeGenerator();

  double GetCharge(double angle);

 private:

  double fK0;
  double fTheta0;
  double fReferenceAngle;
  double fMinSecTheta;
  double fMaxSecTheta;

  unsigned int fNumberOfChargeBins;
  unsigned int fNumberOfChargePDF;

  std::vector<CLHEP::RandGeneral *> fListChargePDF;
  std::vector<double> fListMinCharge;
  std::vector<double> fListMaxCharge;

  bool fIsInitialized;
  utl::RandomEngine* fRandomEngine;

 private:

  void Initialize(void);

  inline double GammaDistribution(double x, double k, double theta) {
    return (pow(x,k-1.0) * exp(-x/theta)/(exp(utl::LogGamma(k)) * pow(theta,k)));
  };

  inline double CumulativeGammaDistribution(double x, double k, double theta) {
    return (boost::math::gamma_p(k,x/theta)); 
    // gamma_p(k,x) is incomplete upper gamma
  };

  inline double InverseCumulativeGammaDistribution(double y, double k, double theta) {
    return (theta*boost::math::gamma_p_inv(k, y));
  };

};

} // End namespace RPCSimulatorLX

#endif