FastJet  3.0.6
ClusterSequence_N2.cc
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2 // $Id: ClusterSequence_N2.cc 2657 2011-11-07 16:14:30Z salam $
3 //
4 // Copyright (c) 2005-2011, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
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28 
29 
30 // The plain N^2 part of the ClusterSequence class -- separated out
31 // from the rest of the class implementation so as to speed up
32 // compilation of this particular part while it is under test.
33 
34 #include "fastjet/internal/ClusterSequence_N2.icc"
35 
36 #include<iostream>
37 
38 FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh
39 
40 
41 using namespace std;
42 
43 
44 //*************************************************************************
45 //
46 // THINGS FOR E+E-
47 //
48 //*************************************************************************
49 
50 
51 //----------------------------------------------------------------------
52 template<> inline void ClusterSequence::_bj_set_jetinfo(
53  EEBriefJet * const jetA, const int _jets_index) const {
54 
55  double E = _jets[_jets_index].E();
56  double scale = E*E; // the default energy scale for the kt alg
57  double p = jet_def().extra_param(); // in case we're ee_genkt
58  switch (_jet_algorithm) {
59  case ee_kt_algorithm:
60  assert(_Rparam > 2.0); // force this to be true! [not best place, but works]
61  // recall that _invR2 is artificially set to 1 for this alg
62  // so that we automatically have dij = scale * 2(1-cos theta_ij)
63  // Normally, _Rparam should be automatically set to 4 from JetDefinition
64  break;
65  case ee_genkt_algorithm:
66  if (p <= 0 && scale < 1e-300) scale = 1e-300; // same dodgy safety as genkt
67  scale = pow(scale,p);
68  break;
69  default:
70  throw Error("Unrecognised jet algorithm");
71  }
72  jetA->kt2 = scale; // "kt2" might one day be renamed as "scale" or some such
73 
74  double norm = _jets[_jets_index].modp2();
75  if (norm > 0) {
76  norm = 1.0/sqrt(norm);
77  jetA->nx = norm * _jets[_jets_index].px();
78  jetA->ny = norm * _jets[_jets_index].py();
79  jetA->nz = norm * _jets[_jets_index].pz();
80  } else {
81  jetA->nx = 0.0;
82  jetA->ny = 0.0;
83  jetA->nz = 1.0;
84  }
85  jetA->_jets_index = _jets_index;
86  // initialise NN info as well
87  jetA->NN_dist = _R2;
88  jetA->NN = NULL;
89 }
90 
91 //----------------------------------------------------------------------
92 // returns the angular distance between the two jets
93 template<> double ClusterSequence::_bj_dist(
94  const EEBriefJet * const jeta,
95  const EEBriefJet * const jetb) const {
96  double dist = 1.0
97  - jeta->nx*jetb->nx
98  - jeta->ny*jetb->ny
99  - jeta->nz*jetb->nz;
100  dist *= 2; // distance is _2_*min(Ei^2,Ej^2)*(1-cos theta)
101  return dist;
102 }
103 
104 
105 
106 // get explicit copies of the two N2 cluster cases we need
107 // plain BriefJet
108 void ClusterSequence::_simple_N2_cluster_BriefJet() {
109  _simple_N2_cluster<BriefJet>();
110 }
111 
112 
113 // e+e- BriefJet
114 void ClusterSequence::_simple_N2_cluster_EEBriefJet() {
115  _simple_N2_cluster<EEBriefJet>();
116 }
117 
118 // //----------------------------------------------------------------------
119 // /// Force instantiation of desired versions of _simple_N2_cluster
120 // ///
121 // /// This is not very elegant...
122 // void ClusterSequence::_dummy_N2_cluster_instantiation() {
123 // _simple_N2_cluster<BriefJet>();
124 // _simple_N2_cluster<EEBriefJet>();
125 // }
126 
127 FASTJET_END_NAMESPACE
128 
fastjet::norm
double norm(const VPoint p)
norm of a vector
Definition: Voronoi.hh:150
fastjet::ee_genkt_algorithm
@ ee_genkt_algorithm
the e+e- genkt algorithm (R > 2 and p=1 gives ee_kt)
Definition: JetDefinition.hh:114
fastjet::ee_kt_algorithm
@ ee_kt_algorithm
the e+e- kt algorithm
Definition: JetDefinition.hh:112