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source: git/external/fastjet/plugins/EECambridge/EECambridgePlugin.cc

Last change on this file was cb80e6f, checked in by Pavel Demin <pavel.demin@…>, 4 years ago

update FastJet library to 3.3.4 and FastJet Contrib library to 1.045

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File size: 3.6 KB
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1//FJSTARTHEADER
2// $Id: EECambridgePlugin.cc 4442 2020-05-05 07:50:11Z soyez $
3//
4// Copyright (c) 2007-2020, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
5//
6//----------------------------------------------------------------------
7// This file is part of FastJet.
8//
9// FastJet is free software; you can redistribute it and/or modify
10// it under the terms of the GNU General Public License as published by
11// the Free Software Foundation; either version 2 of the License, or
12// (at your option) any later version.
13//
14// The algorithms that underlie FastJet have required considerable
15// development. They are described in the original FastJet paper,
16// hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use
17// FastJet as part of work towards a scientific publication, please
18// quote the version you use and include a citation to the manual and
19// optionally also to hep-ph/0512210.
20//
21// FastJet is distributed in the hope that it will be useful,
22// but WITHOUT ANY WARRANTY; without even the implied warranty of
23// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
24// GNU General Public License for more details.
25//
26// You should have received a copy of the GNU General Public License
27// along with FastJet. If not, see <http://www.gnu.org/licenses/>.
28//----------------------------------------------------------------------
29//FJENDHEADER
30
31// fastjet stuff
32#include "fastjet/ClusterSequence.hh"
33#include "fastjet/EECambridgePlugin.hh"
34#include "fastjet/NNH.hh"
35
36// other stuff
37#include <sstream>
38#include <limits>
39
40FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh
41
42using namespace std;
43
44//----------------------------------------------------------------------
45/// class to help run an e+e- Cambridge algorithm
46class EECamBriefJet {
47public:
48 void init(const PseudoJet & jet) {
49 double norm = 1.0/sqrt(jet.modp2());
50 nx = jet.px() * norm;
51 ny = jet.py() * norm;
52 nz = jet.pz() * norm;
53 }
54
55 double distance(const EECamBriefJet * jet) const {
56 double dij = 1 - nx*jet->nx
57 - ny*jet->ny
58 - nz*jet->nz;
59 return dij;
60 }
61
62 double beam_distance() const {
63 return numeric_limits<double>::max();
64 }
65
66private:
67 double nx, ny, nz;
68};
69
70
71string EECambridgePlugin::description () const {
72 ostringstream desc;
73 desc << "EECambridge plugin with ycut = " << ycut() ;
74 return desc.str();
75}
76
77void EECambridgePlugin::run_clustering(ClusterSequence & cs) const {
78 int njets = cs.jets().size();
79 NNH<EECamBriefJet> nnh(cs.jets());
80
81 double Q2 = cs.Q2();
82
83 while (njets > 0) {
84 int i, j, k;
85 // here we get a minimum based on the purely angular variable from the NNH class
86 // (called dij there, but vij in the Cambridge article (which uses dij for
87 // a kt distance...)
88 double vij = nnh.dij_min(i, j); // i,j are return values...
89
90 // next we work out the dij (ee kt distance), and based on its
91 // value decide whether we have soft-freezing (represented here by
92 // a "Beam" clustering) or not
93 double dij;
94 if (j >= 0) {
95 double scale = min(cs.jets()[i].E(), cs.jets()[j].E());
96 dij = 2 * vij * scale * scale;
97 if (dij > Q2 * ycut()) {
98 // we'll call the softer partner a "beam" jet
99 if (cs.jets()[i].E() > cs.jets()[j].E()) std::swap(i,j);
100 j = -1;
101 }
102 } else {
103 // for the last particle left, just use yij = 1
104 dij = Q2;
105 }
106
107 if (j >= 0) {
108 cs.plugin_record_ij_recombination(i, j, dij, k);
109 nnh.merge_jets(i, j, cs.jets()[k], k);
110 } else {
111 cs.plugin_record_iB_recombination(i, dij);
112 nnh.remove_jet(i);
113 }
114 njets--;
115 }
116
117}
118
119FASTJET_END_NAMESPACE // defined in fastjet/internal/base.hh
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