G4ImportanceAlgorithm.cc

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//
// $Id$
//
// ----------------------------------------------------------------------
// GEANT 4 class source file
//
// G4ImportanceAlgorithm.cc
//
// ----------------------------------------------------------------------

#include "G4Types.hh"
#include <sstream>
#include "Randomize.hh"

#include "G4ImportanceAlgorithm.hh"

G4ImportanceAlgorithm::G4ImportanceAlgorithm(): fWorned(false)
{
}

G4ImportanceAlgorithm::~G4ImportanceAlgorithm()
{
}

G4Nsplit_Weight
G4ImportanceAlgorithm::Calculate(G4double ipre,
                                 G4double ipost,
                                 G4double init_w) const
{
  G4Nsplit_Weight nw = {0,0};
  if (ipost>0.){
    if (!(ipre>0.)){
      Error("Calculate() - ipre==0.");
    }
    G4double ipre_over_ipost = ipre/ipost;
    if ((ipre_over_ipost<0.25 || ipre_over_ipost> 4) && !fWorned) {
      std::ostringstream os;
      os << "Calculate() - ipre_over_ipost ! in [0.25, 4]." << G4endl
         << "ipre_over_ipost = " << ipre_over_ipost << ".";
      Warning(os.str());
      fWorned = true;
      if (ipre_over_ipost<=0) {
        Error("Calculate() - ipre_over_ipost<=0.");
      }
    }
    if (init_w<=0.) {
      Error("Calculate() - iniitweight<= 0. found!");
    }

    // default geometrical splitting 
    // in integer mode 
    // for ipre_over_ipost <= 1
    G4double inv = 1./ipre_over_ipost;
    nw.fN = static_cast<G4int>(inv);
    nw.fW = init_w * ipre_over_ipost;
    
    // geometrical splitting for double mode
    if (ipre_over_ipost<1) {
      if ( static_cast<G4double>(nw.fN) != inv) {
        // double mode
        // probability p for splitting into n+1 tracks
        G4double p = inv - nw.fN;
        // get a random number out of [0,1)
        G4double r = G4UniformRand();
        if (r<p) {
          nw.fN++;
        } 
      }  
    }
    // ipre_over_ipost > 1
    //  russian roulett
    else if (ipre_over_ipost>1) {
      // probabiity for killing track
      G4double p = 1-inv;
      // get a random number out of [0,1)
      G4double r = G4UniformRand();
      if (r<p) {
        // kill track
        nw.fN = 0;
        nw.fW = 0;
      }
      else {
        nw.fN = 1;     
      }
    }
  }
  return nw;
}

void G4ImportanceAlgorithm::Error(const G4String &msg) const
{
  G4Exception("G4ImportanceAlgorithm::Error()",
              "GeomBias0002", FatalException, msg);
}

void G4ImportanceAlgorithm::Warning(const G4String &msg) const
{
  G4Exception("G4ImportanceAlgorithm::Warning()",
              "GeomBias1001", JustWarning, msg);
}

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