PrunedRecombiner.cc

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//
// Implements the PrunedRecombiner class.  See PrunedRecombiner.hh
//

#include "RecoJets/JetAlgorithms/interface/PrunedRecombiner.hh"

#include <sstream>

using namespace fastjet;

std::string PrunedRecombiner::description() const
{
    std::ostringstream s;
    s << "Pruned " << _recombiner->description()
      << ", with zcut = " << _zcut << " and Rcut = " << _Rcut;
    return s.str();
}   
    
// Recombine pa and pb and put result into pab.
// If pruning test is true (the recombination is vetoed) the harder
//   parent is merged with a 0 PseudoJet. (Check that this is an identity in
//   all recombination schemes!)
// When a branch is pruned, its cluster_hist_index is stored in 
//   _pruned_pseudojets for later use.
void PrunedRecombiner::recombine(const PseudoJet & pa, const PseudoJet & pb, 
                           PseudoJet & pab) const
{
    PseudoJet p0(0.0, 0.0, 0.0, 0.0);
    // test if recombination should be pruned
    switch ( _pruning_test(pa, pb) ) {
        case 1:
            _pruned_pseudojets.push_back(pb.cluster_hist_index());
            _recombiner->recombine(pa, p0, pab);
            break;
        case 2:
            _pruned_pseudojets.push_back(pa.cluster_hist_index());
            _recombiner->recombine(pb, p0, pab);
            break;
        default: 
            // if no pruning, do regular combination
            _recombiner->recombine(pa, pb, pab);
    }
}

        
// Function to test if two pseudojets should be merged -- ie, to selectively
//   veto mergings.  Should provide possibility to provide this function...
//   Return codes:
//
//   0: Merge.  (Currently, anything other than 1 or 2 will do.)
//   1: Don't merge; keep pa
//   2: Don't merge; keep pb 
//
int PrunedRecombiner::_pruning_test(const PseudoJet & pa, const PseudoJet & pb) const
{
    // create the new jet by recombining the first two, using the normal
    //   recombination scheme
    PseudoJet newjet;   
    _recombiner->recombine(pa, pb, newjet);

    double minpT = pa.perp();
    int hard = 2;  // harder pj is pj2
    double tmp = pb.perp();
    if (tmp < minpT) {
        minpT = tmp;
        hard = 1;  // harder pj is pj1
    }
    
    if ( pa.squared_distance(pb) < _Rcut*_Rcut 
          || minpT > _zcut * newjet.perp() )
        return 0;
    else
        return hard;
}


void PrunedRecombiner::reset(const double & zcut, const double & Rcut)
{
    _pruned_pseudojets.clear();
    _zcut = zcut;
    _Rcut = Rcut;
}