Qjets.cc

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#include "RecoJets/JetAlgorithms/interface/Qjets.h"

using namespace std;

void Qjets::SetRandSeed(unsigned int seed) {
  _rand_seed_set = true;
  _seed = seed;
}

bool Qjets::JetUnmerged(int num) const { return _merged_jets.find(num) == _merged_jets.end(); }

bool Qjets::JetsUnmerged(const JetDistance& jd) const { return JetUnmerged(jd.j1) && JetUnmerged(jd.j2); }

JetDistance Qjets::GetNextDistance() {
  vector<pair<JetDistance, double> > popped_distances;
  double norm(0.);
  JetDistance ret;
  ret.j1 = -1;
  ret.j2 = -1;
  ret.dij = -1.;
  bool dmin_set(false);
  double dmin(0.);

  while (!_distances.empty()) {
    JetDistance dist = _distances.top();
    _distances.pop();
    if (JetsUnmerged(dist)) {
      if (!dmin_set) {
        dmin = dist.dij;
        dmin_set = true;
      }
      double weight = exp(-_rigidity * (dist.dij - dmin) / dmin);
      popped_distances.push_back(make_pair(dist, weight));
      norm += weight;
      if (weight / norm < _truncation_fctr)
        break;
    }
  }

  double rand(Rand()), tot_weight(0.);
  for (vector<pair<JetDistance, double> >::iterator it = popped_distances.begin(); it != popped_distances.end(); it++) {
    tot_weight += (*it).second / norm;
    if (tot_weight >= rand) {
      ret = (*it).first;
      omega *= ((*it).second);
      break;
    }
  }

  // repopulate in reverse (maybe quicker?)
  for (vector<pair<JetDistance, double> >::reverse_iterator it = popped_distances.rbegin();
       it != popped_distances.rend();
       it++)
    if (JetsUnmerged((*it).first))
      _distances.push((*it).first);

  return ret;
}

void Qjets::Cluster(fastjet::ClusterSequence& cs) {
  omega = 1.;
  QjetsBaseExtras* extras = new QjetsBaseExtras();
  computeDCut(cs);

  // Populate all the distances
  ComputeAllDistances(cs.jets());
  JetDistance jd = GetNextDistance();

  while (!_distances.empty() && jd.dij != -1.) {
    if (!Prune(jd, cs)) {
      //      _merged_jets.push_back(jd.j1);
      //      _merged_jets.push_back(jd.j2);
      _merged_jets[jd.j1] = true;
      _merged_jets[jd.j2] = true;

      int new_jet = -1;
      cs.plugin_record_ij_recombination(jd.j1, jd.j2, 1., new_jet);
      if (!JetUnmerged(new_jet))
        edm::LogError("QJets Clustering") << "Problem with FastJet::plugin_record_ij_recombination";
      ComputeNewDistanceMeasures(cs, new_jet);
    } else {
      double j1pt = cs.jets()[jd.j1].perp();
      double j2pt = cs.jets()[jd.j2].perp();
      if (j1pt > j2pt) {
        //  _merged_jets.push_back(jd.j2);
        _merged_jets[jd.j2] = true;
        cs.plugin_record_iB_recombination(jd.j2, 1.);
      } else {
        //  _merged_jets.push_back(jd.j1);
        _merged_jets[jd.j1] = true;
        cs.plugin_record_iB_recombination(jd.j1, 1.);
      }
    }
    jd = GetNextDistance();
  }

  extras->_wij = omega;
  cs.plugin_associate_extras(extras);

  // merge remaining jets with beam
  int num_merged_final(0);
  for (unsigned int i = 0; i < cs.jets().size(); i++)
    if (JetUnmerged(i)) {
      num_merged_final++;
      cs.plugin_record_iB_recombination(i, 1.);
    }

  if (!(num_merged_final < 2))
    edm::LogError("QJets Clustering") << "More than 1 jet remains after reclustering";
}

void Qjets::computeDCut(fastjet::ClusterSequence& cs) {
  // assume all jets in cs form a single jet.  compute mass and pt
  fastjet::PseudoJet sum(0., 0., 0., 0.);
  for (vector<fastjet::PseudoJet>::const_iterator it = cs.jets().begin(); it != cs.jets().end(); it++)
    sum += (*it);
  _dcut = 2. * _dcut_fctr * sum.m() / sum.perp();
}

bool Qjets::Prune(JetDistance& jd, fastjet::ClusterSequence& cs) {
  double pt1 = cs.jets()[jd.j1].perp();
  double pt2 = cs.jets()[jd.j2].perp();
  fastjet::PseudoJet sum_jet = cs.jets()[jd.j1] + cs.jets()[jd.j2];
  double sum_pt = sum_jet.perp();
  double z = min(pt1, pt2) / sum_pt;
  double d2 = cs.jets()[jd.j1].plain_distance(cs.jets()[jd.j2]);
  return (d2 > _dcut * _dcut) && (z < _zcut);
}

void Qjets::ComputeAllDistances(const vector<fastjet::PseudoJet>& inp) {
  for (unsigned int i = 0; i < inp.size() - 1; i++) {
    // jet-jet distances
    for (unsigned int j = i + 1; j < inp.size(); j++) {
      JetDistance jd;
      jd.j1 = i;
      jd.j2 = j;
      if (jd.j1 != jd.j2) {
        jd.dij = d_ij(inp[i], inp[j]);
        _distances.push(jd);
      }
    }
  }
}

void Qjets::ComputeNewDistanceMeasures(fastjet::ClusterSequence& cs, unsigned int new_jet) {
  // jet-jet distances
  for (unsigned int i = 0; i < cs.jets().size(); i++)
    if (JetUnmerged(i) && i != new_jet) {
      JetDistance jd;
      jd.j1 = new_jet;
      jd.j2 = i;
      jd.dij = d_ij(cs.jets()[jd.j1], cs.jets()[jd.j2]);
      _distances.push(jd);
    }
}

double Qjets::d_ij(const fastjet::PseudoJet& v1, const fastjet::PseudoJet& v2) const {
  double p1 = v1.perp();
  double p2 = v2.perp();
  double ret = pow(min(p1, p2), _exp_min) * pow(max(p1, p2), _exp_max) * v1.squared_distance(v2);
  if (edm::isNotFinite(ret))
    edm::LogError("QJets Clustering") << "d_ij is not finite";
  return ret;
}

double Qjets::Rand() {
  double ret = 0.;
  //if(_rand_seed_set)
  //  ret = rand_r(&_seed)/(double)RAND_MAX;
  //else
  //ret = rand()/(double)RAND_MAX;
  ret = _rnEngine->flat();
  return ret;
}