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//FJSTARTHEADER
// $Id$
//
// Copyright (c) 2007-2021, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
//
//----------------------------------------------------------------------
// This file is part of FastJet.
//
// FastJet is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// The algorithms that underlie FastJet have required considerable
// development. They are described in the original FastJet paper,
// hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use
// FastJet as part of work towards a scientific publication, please
// quote the version you use and include a citation to the manual and
// optionally also to hep-ph/0512210.
//
// FastJet is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with FastJet. If not, see <http://www.gnu.org/licenses/>.
//----------------------------------------------------------------------
//FJENDHEADER
// fastjet stuff
#include "fastjet/ClusterSequence.hh"
#include "fastjet/EECambridgePlugin.hh"
#include "fastjet/NNH.hh"
// other stuff
#include <sstream>
#include <limits>
FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh
using namespace std;
//----------------------------------------------------------------------
/// class to help run an e+e- Cambridge algorithm
class EECamBriefJet {
public:
void init(const PseudoJet & jet) {
double norm = 1.0/sqrt(jet.modp2());
nx = jet.px() * norm;
ny = jet.py() * norm;
nz = jet.pz() * norm;
}
double distance(const EECamBriefJet * jet) const {
double dij = 1 - nx*jet->nx
- ny*jet->ny
- nz*jet->nz;
return dij;
}
double beam_distance() const {
return numeric_limits<double>::max();
}
private:
double nx, ny, nz;
};
string EECambridgePlugin::description () const {
ostringstream desc;
desc << "EECambridge plugin with ycut = " << ycut() ;
return desc.str();
}
void EECambridgePlugin::run_clustering(ClusterSequence & cs) const {
int njets = cs.jets().size();
NNH<EECamBriefJet> nnh(cs.jets());
double Q2 = cs.Q2();
while (njets > 0) {
int i, j, k;
// here we get a minimum based on the purely angular variable from the NNH class
// (called dij there, but vij in the Cambridge article (which uses dij for
// a kt distance...)
double vij = nnh.dij_min(i, j); // i,j are return values...
// next we work out the dij (ee kt distance), and based on its
// value decide whether we have soft-freezing (represented here by
// a "Beam" clustering) or not
double dij;
if (j >= 0) {
double scale = min(cs.jets()[i].E(), cs.jets()[j].E());
dij = 2 * vij * scale * scale;
if (dij > Q2 * ycut()) {
// we'll call the softer partner a "beam" jet
if (cs.jets()[i].E() > cs.jets()[j].E()) std::swap(i,j);
j = -1;
}
} else {
// for the last particle left, just use yij = 1
dij = Q2;
}
if (j >= 0) {
cs.plugin_record_ij_recombination(i, j, dij, k);
nnh.merge_jets(i, j, cs.jets()[k], k);
} else {
cs.plugin_record_iB_recombination(i, dij);
nnh.remove_jet(i);
}
njets--;
}
}
FASTJET_END_NAMESPACE // defined in fastjet/internal/base.hh
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