G4SampleResonance.cc

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//
// ------------------------------------------------------------
//      GEANT 4 class header file
//
//      ---------------- G4SampleResonance ----------------
//             by Henning Weber, March 2001.
//      helper class for sampling resonance masses
// ------------------------------------------------------------


#include "globals.hh"
#include <iostream>
#include "G4SampleResonance.hh"
#include "G4DecayTable.hh"
#include "Randomize.hh"
#include "G4HadronicException.hh"

G4SampleResonance::minMassMapType G4SampleResonance::minMassCache;

G4double G4SampleResonance::GetMinimumMass(const G4ParticleDefinition* p) const
{

    G4double minResonanceMass = DBL_MAX;

    if ( p->IsShortLived() )
    {
        minMassMapIterator iter = minMassCache.find(p);
        if ( iter!=minMassCache.end() )
        {
            minResonanceMass = (*iter).second;
        }
        else
        {
            // G4cout << "--> request for " << p->GetParticleName() << G4endl;

            const G4DecayTable* theDecays = const_cast<G4ParticleDefinition*>(p)->GetDecayTable();
            const G4int nDecays = theDecays->entries();

            for (G4int i=0; i<nDecays; i++)
            {
                const G4VDecayChannel* aDecay = theDecays->GetDecayChannel(i);
                const G4int nDaughters = aDecay->GetNumberOfDaughters();

                G4double minChannelMass = 0;

                for (G4int j=0; j<nDaughters; j++)
                {
                    const G4ParticleDefinition* aDaughter = const_cast<G4VDecayChannel*>(aDecay)->GetDaughter(j);
                    G4double minMass = GetMinimumMass(aDaughter);
                    if (!minMass) minMass = DBL_MAX; // exclude gamma channel;
                    minChannelMass+=minMass;
                }
                // G4cout << "channel mass for the above is " << minChannelMass/MeV << G4endl;
                if (minChannelMass < minResonanceMass) minResonanceMass = minChannelMass;

            }
            // replace this as soon as the compiler supports mutable!!
            G4SampleResonance* self = const_cast<G4SampleResonance*>(this);
            (self->minMassCache)[p] = minResonanceMass;

        }
    } 
    else
    {

        minResonanceMass = p->GetPDGMass();

    }
    // G4cout << "minimal mass for " << p->GetParticleName() << " is " << minResonanceMass/MeV << G4endl;

    return minResonanceMass;
} 



G4double G4SampleResonance::SampleMass(const G4ParticleDefinition* p, const G4double maxMass) const
{
    return SampleMass(p->GetPDGMass(), p->GetPDGWidth(), GetMinimumMass(p), maxMass);
}


G4double G4SampleResonance::SampleMass(const G4double poleMass, 
        const G4double gamma,
        const G4double minMass,
        const G4double maxMass) const
{
    // Chooses a mass randomly between minMass and maxMass
    //     according to a Breit-Wigner function with constant
    //     width gamma and pole poleMass

    if ( minMass > maxMass )
    {
        throw G4HadronicException(__FILE__, __LINE__,
                "SampleResonanceMass: mass range negative (minMass>maxMass)");
    }

    G4double returnMass;

    if ( gamma < DBL_EPSILON )
    {
        returnMass = std::max(minMass, std::min(maxMass, poleMass));
    }
    else
    {
        double fmin = BrWigInt0(minMass, gamma, poleMass);
        double fmax = BrWigInt0(maxMass, gamma, poleMass);
        double f = fmin + (fmax-fmin)*G4UniformRand();
        returnMass = BrWigInv(f, gamma, poleMass);
    }

    return returnMass;
}