FastJet  3.0.6
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GridJetPlugin.cc
1 //STARTHEADER
2 // $Id: GridJetPlugin.cc 2268 2011-06-20 15:12:26Z salam $
3 //
4 // Copyright (c) 2011, Matteo Cacciari, Gavin Salam and Gregory Soyez
5 //
6 //----------------------------------------------------------------------
7 // This file is part of FastJet.
8 //
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28 
29 // fastjet stuff
30 #include "fastjet/ClusterSequence.hh"
31 #include "fastjet/GridJetPlugin.hh"
32 
33 // other stuff
34 #include <vector>
35 #include <sstream>
36 
37 FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh
38 
39 using namespace std;
40 
41 //----------------------------------------------------------------------
42 GridJetPlugin::GridJetPlugin (double ymax,
43  double requested_grid_spacing,
44  const JetDefinition & post_jet_def) :
45  _ymin(-ymax), _ymax(ymax),
46  _requested_grid_spacing(requested_grid_spacing) ,
47  _post_jet_def(post_jet_def)
48 {
49  setup_grid();
50 }
51 
52 void GridJetPlugin::setup_grid() {
53  // since we've exchanged the arguments of the constructor,
54  // there's a danger of calls with exchanged ymax,spacing arguments --
55  // the following check should catch most such situations.
56  assert(_ymax>0 && _ymax - _ymin >= _requested_grid_spacing);
57 
58  double ny_double = (_ymax-_ymin) / _requested_grid_spacing;
59  _ny = int(ny_double+0.49999);
60  _dy = (_ymax-_ymin) / _ny;
61 
62  _nphi = int (twopi / _requested_grid_spacing + 0.5);
63  _dphi = twopi / _nphi;
64 
65  // some sanity checking (could throw a fastjet::Error)
66  assert(_ny >= 1 && _nphi >= 1);
67 
68  _ntotal = _nphi * _ny;
69 }
70 
71 
72 //----------------------------------------------------------------------
73 string GridJetPlugin::description () const {
74  ostringstream desc;
75  desc << "GridJetPlugin plugin with ymax = " << _ymax << ", dy = " << _dy << ", dphi = " << _dphi << " (requested grid spacing was " << _requested_grid_spacing << ")";
76  if (_post_jet_def.jet_algorithm() != undefined_jet_algorithm) {
77  desc << ", followed by " << _post_jet_def.description();
78  }
79  return desc.str();
80 }
81 
82 
83 //----------------------------------------------------------------------
84 double GridJetPlugin::R() const {return sqrt(_dy*_dphi/pi);}
85 
86 
87 //----------------------------------------------------------------------
88 int GridJetPlugin::igrid(const PseudoJet & p) const {
89  // directly taking int does not work for values between -1 and 0
90  // so use floor instead
91  // double iy_double = (p.rap() - _ymin) / _dy;
92  // if (iy_double < 0.0) return -1;
93  // int iy = int(iy_double);
94  // if (iy >= _ny) return -1;
95 
96  // writing it as below gives a huge speed gain (factor two!). Even
97  // though answers are identical and the routine here is not the
98  // speed-critical step. It's not at all clear why.
99  int iy = int(floor( (p.rap() - _ymin) / _dy ));
100  if (iy < 0 || iy >= _ny) return -1;
101 
102  int iphi = int( p.phi()/_dphi );
103  assert(iphi >= 0 && iphi <= _nphi);
104  if (iphi == _nphi) iphi = 0; // just in case of rounding errors
105 
106  int igrid_res = iy*_nphi + iphi;
107  assert (igrid_res >= 0 && igrid_res < _ny*_nphi);
108  return igrid_res;
109 }
110 
111 
112 //----------------------------------------------------------------------
114 
115  // we will create a grid;
116  // * -1 will indicate there is no jet here currently
117  // * a number >= 0 will mean that particle indicated by the index
118  // is currently the jet on the grid
119  vector<int> grid(_ntotal, -1);
120 
121  int nparticles = cs.jets().size();
122  double dij_or_diB = 1.0;
123 
124  int ngrid_active = 0;
125 
126  // combine particles with whatever is in the grid
127  for (int i = 0; i < nparticles; i++) {
128  int igrd = igrid(cs.jets()[i]);
129  //cout << i << " " << cs.jets()[i].rap() << " " << cs.jets()[i].phi()
130  // << " " << igrd << " " << grid.size() << " " << _ntotal << endl;
131  if (igrd < 0) continue;
132  assert(igrd <= _ntotal);
133  if (grid[igrd] == -1) {
134  grid[igrd] = i; // jet index of initial particle i is i
135  ngrid_active++;
136  } else {
137  int k;
138  cs.plugin_record_ij_recombination(grid[igrd], i, dij_or_diB, k);
139  grid[igrd] = k; // grid takes jet index of new particle
140  //cout << " res: " << cs.jets()[k].rap() << " " << cs.jets()[k].phi() << endl;
141  }
142  }
143 
144  if (_post_jet_def.jet_algorithm() == undefined_jet_algorithm) {
145  // make the final jets via iB recombinations
146  for (unsigned igrd = 0; igrd < grid.size(); igrd++) {
147  if (grid[igrd] != -1) cs.plugin_record_iB_recombination(grid[igrd],
148  dij_or_diB);
149  }
150  } else {
151  // otherwise post-cluster the grid elements with a normal jet algorithm
152  vector<PseudoJet> inputs;
153  vector<int> cs_indices;
154  inputs.reserve(ngrid_active);
155  cs_indices.reserve(2*ngrid_active);
156  for (unsigned igrd = 0; igrd < grid.size(); igrd++) {
157  if (grid[igrd] != -1) {
158  inputs.push_back(cs.jets()[grid[igrd]]);
159  cs_indices.push_back(grid[igrd]);
160  }
161  }
162  ClusterSequence post_cs(inputs, _post_jet_def);
163  const vector<ClusterSequence::history_element> & post_history = post_cs.history();
164  const vector<PseudoJet> & post_jets = post_cs.jets();
165  for (unsigned ihist = ngrid_active; ihist < post_history.size(); ihist++) {
166  const ClusterSequence::history_element & hist = post_history[ihist];
167  int post_ij1 = post_history[hist.parent1].jetp_index;
168  int ij1 = cs_indices[post_ij1];
169  if (hist.parent2 >= 0) {
170  int post_ij2 = post_history[hist.parent2].jetp_index;
171  int ij2 = cs_indices[post_ij2];
172  int k;
173  cs.plugin_record_ij_recombination(ij1, ij2, hist.dij, post_jets[hist.jetp_index], k);
174  assert(int(cs_indices.size()) == hist.jetp_index);
175  cs_indices.push_back(k);
176  } else {
177  cs.plugin_record_iB_recombination(ij1, hist.dij);
178  }
179  }
180 
181  }
182 }
183 
184 FASTJET_END_NAMESPACE // defined in fastjet/internal/base.hh
double rap() const
returns the rapidity or some large value when the rapidity is infinite
Definition: PseudoJet.hh:121
const std::vector< PseudoJet > & jets() const
allow the user to access the internally stored _jets() array, which contains both the initial particl...
deals with clustering
the value for the jet algorithm in a JetDefinition for which no algorithm has yet been defined ...
JetAlgorithm jet_algorithm() const
return information about the definition...
virtual std::string description() const
return a textual description of the jet-definition implemented in this plugin
int jetp_index
index in _history where the current jet is recombined with another jet to form its child...
void plugin_record_ij_recombination(int jet_i, int jet_j, double dij, int &newjet_k)
record the fact that there has been a recombination between jets()[jet_i] and jets()[jet_k], with the specified dij, and return the index (newjet_k) allocated to the new jet, whose momentum is assumed to be the 4-vector sum of that of jet_i and jet_j
virtual double R() const
This returns the sqrt(dphi*dy/pi) – i.e.
int parent2
index in _history where first parent of this jet was created (InexistentParent if this jet is an orig...
double dij
index in the _jets vector where we will find the
void plugin_record_iB_recombination(int jet_i, double diB)
record the fact that there has been a recombination between jets()[jet_i] and the beam...
std::string description() const
return a textual description of the current jet definition
const std::vector< history_element > & history() const
allow the user to access the raw internal history.
a single element in the clustering history
double phi() const
returns phi (in the range 0..2pi)
Definition: PseudoJet.hh:106
virtual void run_clustering(ClusterSequence &) const
given a ClusterSequence that has been filled up with initial particles, the following function should...
Class to contain pseudojets, including minimal information of use to jet-clustering routines...
Definition: PseudoJet.hh:65
class that is intended to hold a full definition of the jet clusterer