G4BOptnLeadingParticle.cc

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// G4BOptnLeadingParticle
// --------------------------------------------------------------------
 
#include "G4BOptnLeadingParticle.hh"
#include "G4BiasingProcessInterface.hh"
 
#include <vector>
#include <map>
 
 
G4BOptnLeadingParticle::G4BOptnLeadingParticle(const G4String& name)
  : G4VBiasingOperation( name )
{
}
 
G4BOptnLeadingParticle::~G4BOptnLeadingParticle()
{
}
 
G4VParticleChange* G4BOptnLeadingParticle::
ApplyFinalStateBiasing( const G4BiasingProcessInterface* callingProcess,
                        const G4Track* track, const G4Step* step, G4bool& )
{
  // -- collect wrapped process particle change:
  auto wrappedProcessParticleChange = callingProcess->GetWrappedProcess()->PostStepDoIt(*track,*step);
 
  // -- does nothing in case the primary stays alone or in weird situation where all are killed...
  if ( wrappedProcessParticleChange->GetNumberOfSecondaries() == 0 )                        return wrappedProcessParticleChange;
  if ( wrappedProcessParticleChange->GetTrackStatus()         == fKillTrackAndSecondaries ) return wrappedProcessParticleChange;
  // -- ... else, collect the secondaries in a same vector (the primary is pushed in this vector, if surviving, later see [**]):
  std::vector < G4Track* > secondariesAndPrimary;
  for ( auto i = 0 ; i < wrappedProcessParticleChange->GetNumberOfSecondaries() ; i++ ) secondariesAndPrimary.push_back(  wrappedProcessParticleChange->GetSecondary( i ) );
  
 
  // -- If case the primary survives, need to collect its new state. In the general case of the base class G4VParticleChange
  // -- this is tricky, as this class does not hold the primary changes (and we have to build a fake step and fake track
  // -- caring about the touchables, etc.) So we limit here to the G4ParticleChange case, checking the reality of this
  // -- class with a dynamic cast. If we don't have such an actual G4DynamicParticle object, we give up the biasing and return
  // -- the untrimmed process final state.
  // -- Note that this case does not happen often, as the technique is intended for inelastic processes. For case where several
  // -- particles can be produced without killing the primary, we have for example the electron-/positron-nuclear
  G4ParticleChange* castParticleChange ( nullptr );
  G4Track*          finalStatePrimary  ( nullptr );
  if ( ( wrappedProcessParticleChange->GetTrackStatus() != fStopAndKill ) )
  {
    // fFakePrimaryTrack->CopyTrackInfo( *track );
    // fFakeStep        ->InitializeStep( fFakePrimaryTrack );
    // wrappedProcessParticleChange->UpdateStepForPostStep( fFakeStep );
    // fFakeStep->UpdateTrack();
    castParticleChange = dynamic_cast< G4ParticleChange* >( wrappedProcessParticleChange );
    if ( castParticleChange == nullptr )
    {
      G4cout << " **** G4BOptnLeadingParticle::ApplyFinalStateBiasing(...) : can not bias for " << callingProcess->GetProcessName() << ", this is just a warning." << G4endl;
      return wrappedProcessParticleChange;
    }
    finalStatePrimary = new G4Track( *track );
    finalStatePrimary->SetKineticEnergy ( castParticleChange->GetEnergy() );
    finalStatePrimary->SetWeight ( castParticleChange->GetWeight() );
    finalStatePrimary->SetMomentumDirection( *(castParticleChange->GetMomentumDirection()) );
    // -- [**] push the primary as the last track in the vector of tracks:
    secondariesAndPrimary.push_back( finalStatePrimary );
  }
  
  // -- Ensure the secondaries all have the primary weight:
  // ---- collect primary track weight, from updated by process if alive, or from original copy if died:
  G4double primaryWeight;
  if ( finalStatePrimary ) primaryWeight = finalStatePrimary->GetWeight();
  else primaryWeight = track->GetWeight();
  // ---- now set this same weight to all secondaries:
  for (auto i = 0; i < wrappedProcessParticleChange->GetNumberOfSecondaries(); ++i)
    secondariesAndPrimary[ i ]->SetWeight( primaryWeight );
 
  // -- finds the leading particle, initialize a map of surviving tracks, tag as surviving the leading track:
  std::size_t leadingIDX = 0;
  G4double leadingEnergy = -1;
  std::map< G4Track*, G4bool > survivingMap;
  for ( std::size_t idx = 0; idx < secondariesAndPrimary.size(); ++idx )
  {
    survivingMap[ secondariesAndPrimary[idx] ] = false;
    if ( secondariesAndPrimary[idx]->GetKineticEnergy() > leadingEnergy )
    {
      leadingEnergy = secondariesAndPrimary[idx]->GetKineticEnergy();
      leadingIDX    = idx;
    }
  }
  survivingMap[ secondariesAndPrimary[leadingIDX] ] = true; // -- tag as surviving the leading particle
 
  // -- now make track vectors of given types ( choose type = abs(PDG) ), excluding the leading particle:
  std::map < G4int, std::vector< G4Track* > > typesAndTracks;
  for ( std::size_t idx = 0; idx < secondariesAndPrimary.size(); ++idx )
  {
    if ( idx == leadingIDX ) continue; // -- excludes the leading particle
    auto currentTrack = secondariesAndPrimary[idx];
    auto GROUP        = std::abs( currentTrack->GetDefinition()->GetPDGEncoding() ); // -- merge particles and anti-particles in the same category  -- §§ this might be proposed as an option in future
    if ( currentTrack->GetDefinition()->GetBaryonNumber() >= 2 )
      GROUP = -1000; // -- merge all baryons above proton/neutron in one same group -- §§ might be proposed as an option too
 
    if ( typesAndTracks.find( GROUP ) == typesAndTracks.cend() )
    {
      std::vector< G4Track* > v;
      v.push_back( currentTrack );
      typesAndTracks[ GROUP ] = std::move(v);
    }
    else
    {
      typesAndTracks[ GROUP ].push_back( currentTrack );
    }
  }
  // -- and on these vectors, randomly select the surviving particles:
  // ---- randomly select one surviving track per species
  // ---- for this surviving track, further apply a Russian roulette
  G4int nSecondaries = 0; // -- the number of secondaries to be returned
  for ( auto& typeAndTrack : typesAndTracks )
  {
    std::size_t nTracks = (typeAndTrack.second).size();
    G4Track* keptTrack;
    // -- select one track among ones in same species:
    if ( nTracks > 1 )
    {
      auto keptTrackIDX = G4RandFlat::shootInt( nTracks );
      keptTrack = (typeAndTrack.second)[keptTrackIDX];
      keptTrack->SetWeight( keptTrack->GetWeight() * nTracks );
    }
    else
    {
      keptTrack = (typeAndTrack.second)[0];
    }
    // -- further apply a Russian Roulette on it:
    G4bool keepTrack = false;
    if ( fRussianRouletteKillingProbability > 0.0 )
    {
      if ( G4UniformRand() > fRussianRouletteKillingProbability )
      {
        keptTrack->SetWeight( keptTrack->GetWeight() / (1. - fRussianRouletteKillingProbability) );
        keepTrack = true;
      }
    }
    else keepTrack = true;
    if ( keepTrack )
    {
      survivingMap[ keptTrack ] = true;
      if ( keptTrack != finalStatePrimary ) ++nSecondaries;
    }
  }
  // -- and if the leading is not the primary, we have to count it in nSecondaries:
  if ( secondariesAndPrimary[leadingIDX] != finalStatePrimary ) ++nSecondaries;
  
  // -- verify if the primary is still alive or not after above selection:
  G4bool primarySurvived = false;
  if ( finalStatePrimary )
    primarySurvived = survivingMap[ finalStatePrimary ];
    
  
  // -- fill the trimmed particle change:
  // ---- fill for the primary:
  fParticleChange.Initialize(*track);
  if ( primarySurvived )
  {
    fParticleChange.ProposeTrackStatus ( wrappedProcessParticleChange->GetTrackStatus() );
    fParticleChange.ProposeParentWeight ( finalStatePrimary->GetWeight() );
      // -- take weight from copy of primary, this one being updated in the
      //    random selection loop above
    fParticleChange.ProposeEnergy ( finalStatePrimary->GetKineticEnergy() );
    fParticleChange.ProposeMomentumDirection ( finalStatePrimary->GetMomentumDirection() );
  }
  else
  {
    fParticleChange.ProposeTrackStatus ( fStopAndKill );
    fParticleChange.ProposeParentWeight( 0.0 );
    fParticleChange.ProposeEnergy      ( 0.0 );
    }
  // -- fill for surviving secondaries:
  fParticleChange.SetSecondaryWeightByProcess(true);
  fParticleChange.SetNumberOfSecondaries(nSecondaries);
  // ---- note we loop up to on the number of secondaries, which excludes the primary, last in secondariesAndPrimary vector:
  //////  G4cout << callingProcess->GetProcessName() << " :";
  for ( auto idx = 0 ; idx < wrappedProcessParticleChange->GetNumberOfSecondaries() ; ++idx )
  {
    G4Track* secondary = secondariesAndPrimary[idx];
    // ********************
    //// if ( !survivingMap[ secondary ] ) G4cout << " [";
    ///// else G4cout << " ";
    ///// G4cout << secondary->GetDefinition()->GetParticleName() << " " << secondary->GetKineticEnergy();
    ///// if ( !survivingMap[ secondary ] ) G4cout << "]";
    //// if ( secondary ==  secondariesAndPrimary[leadingIDX] ) G4cout << " ***";
    // ******************
    if ( survivingMap[ secondary ] )
      fParticleChange.AddSecondary( secondary );
    else
      delete secondary;
  }
  ///  G4cout << G4endl;
  
  // -- clean the wrapped process particle change:
  wrappedProcessParticleChange->Clear();
 
  if ( finalStatePrimary ) delete finalStatePrimary;  
 
  // -- finally, returns the trimmed particle change:
  return &fParticleChange;
}