/data/refman/pasoursint/CMSSW_5_3_0/src/PhysicsTools/HepMCCandAlgos/src/GenParticlesHelper.cc

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#include "PhysicsTools/HepMCCandAlgos/interface/GenParticlesHelper.h"
#include "DataFormats/HepMCCandidate/interface/GenParticle.h"


using namespace reco;

namespace GenParticlesHelper {

  void 
  findParticles(const reco::GenParticleCollection& sourceParticles, reco::GenParticleRefVector& particleRefs, int pdgId, int status ) {

    unsigned index = 0;
    for(IG ig = sourceParticles.begin(); 
        ig!= sourceParticles.end(); ++ig, ++index) {
 
      const GenParticle& gen = *ig;
    
      // status has been specified, and this one does not have the correct
      // status
      if(status && gen.status()!=status ) continue;
    
      if( std::abs(gen.pdgId()) == pdgId ) {
        GenParticleRef genref( &sourceParticles, index );
        particleRefs.push_back( genref );
      }
    }
  }


  void 
  findDescendents(const reco::GenParticleRef& base, 
                  reco::GenParticleRefVector& descendents, 
                  int status, int pdgId ) {


    const GenParticleRefVector& daughterRefs = base->daughterRefVector();
  
    for(IGR idr = daughterRefs.begin(); 
        idr!= daughterRefs.end(); ++idr ) {
    
      if( (*idr)->status() == status && 
          (!pdgId || std::abs((*idr)->pdgId()) == pdgId) ) {
      
        // cout<<"adding "<<(*idr)<<endl;
        descendents.push_back(*idr);
      }
      else 
        findDescendents( *idr, descendents, status, pdgId );
    }
  }



  void 
  findSisters(const reco::GenParticleRef& baseSister, 
              GenParticleRefVector& sisterRefs) {
  
    assert( baseSister->numberOfMothers() > 0 );
  
    // get first mother 
    const GenParticleRefVector& mothers = baseSister->motherRefVector();
  
    // get sisters 
    const GenParticleRefVector allRefs 
      = mothers[0]->daughterRefVector();
  
    typedef GenParticleRefVector::const_iterator IT;
    for(IT id = allRefs.begin();
        id != allRefs.end();
        ++id ) {
    
      if( *id == baseSister ) { 
        continue; // this is myself
      }
      else 
        sisterRefs.push_back( *id );
    }
  }

  bool 
  isDirect(const reco::GenParticleRef& particle) {
    assert( (particle->status() != 0) && (particle->status() < 4 ) );
    if( particle->status() == 3 )
      return true;
    else {
      assert( particle->numberOfMothers() > 0 );
  
      // get first mother 
      const GenParticleRefVector& mothers = particle->motherRefVector();
      if( mothers[0]->status() == 3 )
        return true;
      else
        return false;
    }
  }


  bool hasAncestor( const reco::GenParticle* particle,
                    int pdgId, int status )  {    
 
    if( particle->pdgId() == pdgId && 
        particle->status() == status )
      return true;

    const GenParticleRefVector& mothers = particle->motherRefVector();
    
    for( IGR im = mothers.begin(); im!=mothers.end(); ++im) {
      const GenParticle& part = **im;
      if( hasAncestor( &part, pdgId, status) )
        return true;
    } 

    return false;
  }


  std::ostream& operator<<( std::ostream& out, 
                            const reco::GenParticleRef& genRef ) {
    
    if(!out) return out;
    
    out<<genRef.key()<<" "<<genRef->pt();
    
    return out;
  }

}