G4ILawTruncatedExp.cc

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// G4ILawTruncatedExp
// --------------------------------------------------------------------
 
#include "G4ILawTruncatedExp.hh"
#include "Randomize.hh"
#include "G4Track.hh"
 
 
G4ILawTruncatedExp::G4ILawTruncatedExp(const G4String& name)
  : G4VBiasingInteractionLaw(name)
{}
 
G4ILawTruncatedExp::~G4ILawTruncatedExp()
{}
 
void G4ILawTruncatedExp::SetForceCrossSection(G4double crossSection)
{
  if (crossSection < 0.0)
  {
    G4Exception("G4ILawTruncatedExp::SetForceCrossSection(..)",
                "BIAS.GEN.09", JustWarning,
                "Cross-section value passed is negative. It is set to zero !");
    fIsSingular  = true;
    crossSection = 0.0;
  }
  fIsSingular = false;
  fCrossSectionDefined = true;
  fCrossSection = crossSection;
}
 
G4double G4ILawTruncatedExp::
ComputeEffectiveCrossSectionAt(G4double distance) const
{
  if ( !fCrossSectionDefined )
  {
    G4Exception("G4ILawTruncatedExp::ComputeEffectiveCrossSection(..)",
                "BIAS.GEN.10", JustWarning,
                "Cross-section value requested, but has not been defined yet. Assumes 0 !");
    // -- zero cross-section, returns the limit form of the effective cross-section:
    return 1.0 / ( fMaximumDistance - distance );
  }
 
  G4double denum = 1.0 - std::exp(-fCrossSection *(fMaximumDistance-distance));
  return fCrossSection/denum;
}
 
G4double G4ILawTruncatedExp::
ComputeNonInteractionProbabilityAt(G4double distance) const
{
  if (!fCrossSectionDefined)
  {
    G4Exception("G4ILawTruncatedExp::ComputeNonInteractionProbability(..)",
                "BIAS.GEN.11", JustWarning,
                "Non interaction probability value requested, but cross section has not been defined yet. Assumes it to be 0 !");
    // -- return limit case of null cross-section:
    return 1.0 - distance / fMaximumDistance;
  }
  G4double   num = 1.0 - std::exp( -fCrossSection*distance         );
  G4double denum = 1.0 - std::exp( -fCrossSection*fMaximumDistance );
  return 1.0 - num/denum;
}
 
G4double G4ILawTruncatedExp::SampleInteractionLength()
{
  if ( !fCrossSectionDefined )
  {
    G4Exception("G4ILawTruncatedExp::Sample(..)",
                "BIAS.GEN.12", JustWarning,
                "Trying to sample while cross-section is not defined, assuming 0 !");
    fInteractionDistance = G4UniformRand() * fMaximumDistance;
    return fInteractionDistance;
  }
  fInteractionDistance = -std::log(1.0-G4UniformRand()*(1.0-std::exp(-fCrossSection*fMaximumDistance)))/fCrossSection;
  return fInteractionDistance;
}
 
G4double G4ILawTruncatedExp::
UpdateInteractionLengthForStep(G4double truePathLength)
{
  fInteractionDistance -= truePathLength;
  fMaximumDistance     -= truePathLength;
  
  if ( fInteractionDistance < 0 )
  {
    G4ExceptionDescription ed;
    ed << " Negative number of interaction length for `" << GetName()
       << "' " << fInteractionDistance << ", set it to zero !" << G4endl; 
    G4Exception("G4ILawTruncatedExp::UpdateInteractionLengthForStep(...)",
                "BIAS.GEN.13", JustWarning,
                "Trying to sample while cross-section is not defined, assuming 0 !");
    fInteractionDistance = 0.;
  }
 
  return  fInteractionDistance;
}