FastJet  3.3.0
06-area.cc
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1 //----------------------------------------------------------------------
2 /// \file
3 /// \page Example06 06 - using jet areas
4 ///
5 /// fastjet example program for jet areas
6 /// It mostly illustrates the usage of the
7 /// fastjet::AreaDefinition and fastjet::ClusterSequenceArea classes
8 ///
9 /// run it with : ./06-area < data/single-event.dat
10 ///
11 /// Source code: 06-area.cc
12 //----------------------------------------------------------------------
13 
14 //STARTHEADER
15 // $Id: 06-area.cc 2684 2011-11-14 07:41:44Z soyez $
16 //
17 // Copyright (c) 2005-2011, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
18 //
19 //----------------------------------------------------------------------
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21 //
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41 
42 #include "fastjet/ClusterSequenceArea.hh" // use this instead of the "usual" ClusterSequence to get area support
43 #include <iostream> // needed for io
44 #include <cstdio> // needed for io
45 
46 using namespace std;
47 
48 /// an example program showing how to use fastjet
49 int main(){
50 
51  // read in input particles
52  //----------------------------------------------------------
53  vector<fastjet::PseudoJet> input_particles;
54 
55  double px, py , pz, E;
56  while (cin >> px >> py >> pz >> E) {
57  // create a fastjet::PseudoJet with these components and put it onto
58  // back of the input_particles vector
59  input_particles.push_back(fastjet::PseudoJet(px,py,pz,E));
60  }
61 
62 
63  // create a jet definition:
64  // a jet algorithm with a given radius parameter
65  //----------------------------------------------------------
66  double R = 0.6;
68 
69 
70  // Now we also need an AreaDefinition to define the properties of the
71  // area we want
72  //
73  // This is made of 2 building blocks:
74  // - the area type:
75  // passive, active, active with explicit ghosts, or Voronoi area
76  // - the specifications:
77  // a VoronoiSpec or a GhostedAreaSpec for the 3 ghost-bases ones
78  //
79  //---------------------------------------------------------- For
80  // GhostedAreaSpec (as below), the minimal info you have to provide
81  // is up to what rapidity ghosts are placed.
82  // Other commonm parameters (that mostly have an impact on the
83  // precision on the area) include the number of repetitions
84  // (i.e. the number of different sets of ghosts that are used) and
85  // the ghost density (controlled through the ghost_area).
86  // Other, more exotic, parameters (not shown here) control how ghosts
87  // are placed.
88  //
89  // The ghost rapidity interval should be large enough to cover the
90  // jets for which you want to calculate. E.g. if you want to
91  // calculate the area of jets up to |y|=4, you need to put ghosts up
92  // to at least 4+R (or, optionally, up to the largest particle
93  // rapidity if this is smaller).
94  double maxrap = 5.0;
95  unsigned int n_repeat = 3; // default is 1
96  double ghost_area = 0.01; // this is the default
97  fastjet::GhostedAreaSpec area_spec(maxrap, n_repeat, ghost_area);
98 
99  fastjet::AreaDefinition area_def(fastjet::active_area, area_spec);
100 
101  // run the jet clustering with the above jet and area definitions
102  //
103  // The only change is the usage of a ClusterSequenceArea rather than
104  //a ClusterSequence
105  //----------------------------------------------------------
106  fastjet::ClusterSequenceArea clust_seq(input_particles, jet_def, area_def);
107 
108 
109  // get the resulting jets ordered in pt
110  //----------------------------------------------------------
111  double ptmin = 5.0;
112  vector<fastjet::PseudoJet> inclusive_jets = sorted_by_pt(clust_seq.inclusive_jets(ptmin));
113 
114 
115  // tell the user what was done
116  // - the description of the algorithm and area used
117  // - extract the inclusive jets with pt > 5 GeV
118  // show the output as
119  // {index, rap, phi, pt, number of constituents}
120  //----------------------------------------------------------
121  cout << endl;
122  cout << "Ran " << jet_def.description() << endl;
123  cout << "Area: " << area_def.description() << endl << endl;
124 
125  // label the columns
126  printf("%5s %15s %15s %15s %15s %15s\n","jet #", "rapidity", "phi", "pt", "area", "area error");
127 
128  // print out the details for each jet
129  for (unsigned int i = 0; i < inclusive_jets.size(); i++) {
130  printf("%5u %15.8f %15.8f %15.8f %15.8f %15.8f\n", i,
131  inclusive_jets[i].rap(), inclusive_jets[i].phi(), inclusive_jets[i].perp(),
132  inclusive_jets[i].area(), inclusive_jets[i].area_error());
133  }
134 
135  return 0;
136 }
General class for user to obtain ClusterSequence with additional area information.
std::vector< PseudoJet > inclusive_jets(const double ptmin=0.0) const
return a vector of all jets (in the sense of the inclusive algorithm) with pt >= ptmin.
the longitudinally invariant kt algorithm
class that holds a generic area definition
int main()
an example program showing how to use fastjet
Definition: 06-area.cc:49
std::string description() const
return a description of the current area definition
std::string description() const
return a textual description of the current jet definition
Parameters to configure the computation of jet areas using ghosts.
Class to contain pseudojets, including minimal information of use to jet-clustering routines...
Definition: PseudoJet.hh:67
class that is intended to hold a full definition of the jet clusterer