G4Poisson.hh File Reference

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

Go to the source code of this file.

Functions
G4long	G4Poisson (G4double mean)

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Function Documentation

G4long G4Poisson

(

G4double

mean

)

[inline]

Definition at line 50 of file G4Poisson.hh.

References G4UniformRand, and position.

Referenced by G4WilsonAbrasionModel::ApplyYourself(), G4ShellVacancy::GenerateNumberOfIonisations(), G4ForwardXrayTR::GetEnergyTR(), G4VEnergyLoss::GetLossWithFluct(), G4VeLowEnergyLoss::GetLossWithFluct(), G4NeutronHPPhotonDist::GetPhotons(), G4PAIySection::GetStepCerenkovLoss(), G4PAIxSection::GetStepCerenkovLoss(), G4PAIySection::GetStepEnergyLoss(), G4PAIxSection::GetStepEnergyLoss(), G4PAIxSection::GetStepMMLoss(), G4PAIySection::GetStepPlasmonLoss(), G4PAIxSection::GetStepPlasmonLoss(), G4PAIxSection::GetStepResonanceLoss(), G4Scintillation::PostStepDoIt(), G4OpWLS::PostStepDoIt(), G4ForwardXrayTR::PostStepDoIt(), G4Cerenkov::PostStepDoIt(), G4RPGTwoCluster::ReactionStage(), G4RPGTwoBody::ReactionStage(), G4RPGFragmentation::ReactionStage(), G4NeutronHPProduct::Sample(), G4UniversalFluctuation::SampleFluctuations(), G4BohrFluctuations::SampleFluctuations(), and G4NeutronHPFSFissionFS::SampleNeutronMult().

{
  G4long number = 0;
  const G4int border = 16;
  G4double limit = 2e9;

  if(mean <= border) {
    G4double position = G4UniformRand();
    G4double poissonValue = std::exp(-mean);
    G4double poissonSum = poissonValue;

    while(poissonSum <= position) {
      number++ ;
      poissonValue *= mean/number;
      poissonSum += poissonValue;
    }
    return number;
  } // the case of mean <= 16

  G4double value, t, y;
  t = std::sqrt(-2*std::log(G4UniformRand()));
  y = CLHEP::twopi*G4UniformRand();
  t *= std::cos(y);
  value = mean + t*std::sqrt(mean) + 0.5;
  if(value <= 0) {return 0;}
  if(value >= limit) { return G4long(limit);}
  return G4long(value);
}

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