G4Poisson.hh File Reference

#include <CLHEP/Units/PhysicalConstants.h>
#include "G4Exp.hh"
#include "G4Types.hh"
#include "Randomize.hh"

Go to the source code of this file.

Functions
G4long	G4Poisson (G4double mean)

Function Documentation

G4Poisson()

G4long G4Poisson ( G4double  mean )

inline

Definition at line 50 of file G4Poisson.hh.

{
  G4long number        = 0;
  const G4int border   = 16;
  const G4double limit = 2e9;
 
  if(mean <= border)
  {
    G4double position     = G4UniformRand();
    G4double poissonValue = G4Exp(-mean);
    G4double poissonSum   = poissonValue;
 
    while(poissonSum <= position)
    {
      ++number;
      poissonValue *= mean / number;
      poissonSum += poissonValue;
    }
    return number;
  }  // the case of mean <= 16
 
  G4double t = std::sqrt(-2. * std::log(G4UniformRand())) *
               std::cos(2. * CLHEP::pi * G4UniformRand());
  G4double value = mean + t * std::sqrt(mean) + 0.5;
  if(value < 0.)
  {
    return 0;
  }
  return (value >= limit) ? G4long(limit) : G4long(value);
}

References G4Exp(), G4UniformRand, and CLHEP::pi.

Referenced by G4UniversalFluctuation::AddExcitation(), G4WilsonAbrasionModel::ApplyYourself(), G4hImpactIonisation::ElectronicLossFluctuation(), G4ShellVacancy::GenerateNumberOfIonisations(), G4ForwardXrayTR::GetEnergyTR(), G4ParticleHPProduct::GetMultiplicity(), G4ParticleHPPhotonDist::GetPhotons(), G4PAIxSection::GetStepCerenkovLoss(), G4PAIySection::GetStepCerenkovLoss(), G4PAIxSection::GetStepEnergyLoss(), G4PAIySection::GetStepEnergyLoss(), G4PAIxSection::GetStepMMLoss(), G4PAIxSection::GetStepPlasmonLoss(), G4PAIySection::GetStepPlasmonLoss(), G4PAIxSection::GetStepResonanceLoss(), G4Cerenkov::PostStepDoIt(), G4ForwardXrayTR::PostStepDoIt(), G4Scintillation::PostStepDoIt(), G4OpWLS::PostStepDoIt(), G4OpWLS2::PostStepDoIt(), G4PAIPhotData::SampleAlongStepPhotonTransfer(), G4PAIPhotData::SampleAlongStepPlasmonTransfer(), G4PAIPhotData::SampleAlongStepTransfer(), G4PAIModelData::SampleAlongStepTransfer(), G4UniversalFluctuation::SampleGlandz(), G4UrbanFluctuation::SampleGlandz(), and G4ParticleHPFSFissionFS::SampleNeutronMult().