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;
}