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source: svn/trunk/external/fastjet/tools/GridMedianBackgroundEstimator.hh@ 1393

Last change on this file since 1393 was 999, checked in by Pavel Demin, 12 years ago

add fastjet/tools

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1#ifndef __GRID_MEDIAN_BACKGROUND_ESTIMATOR_HH__
2#define __GRID_MEDIAN_BACKGROUND_ESTIMATOR_HH__
3
4//STARTHEADER
5// $Id: GridMedianBackgroundEstimator.hh 2580 2011-09-13 17:25:43Z salam $
6//
7// Copyright (c) 2005-2011, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
8//
9//----------------------------------------------------------------------
10// This file is part of FastJet.
11//
12// FastJet is free software; you can redistribute it and/or modify
13// it under the terms of the GNU General Public License as published by
14// the Free Software Foundation; either version 2 of the License, or
15// (at your option) any later version.
16//
17// The algorithms that underlie FastJet have required considerable
18// development and are described in hep-ph/0512210. If you use
19// FastJet as part of work towards a scientific publication, please
20// include a citation to the FastJet paper.
21//
22// FastJet is distributed in the hope that it will be useful,
23// but WITHOUT ANY WARRANTY; without even the implied warranty of
24// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
25// GNU General Public License for more details.
26//
27// You should have received a copy of the GNU General Public License
28// along with FastJet. If not, see <http://www.gnu.org/licenses/>.
29//----------------------------------------------------------------------
30//ENDHEADER
31
32
33#include "fastjet/tools/BackgroundEstimatorBase.hh"
34
35FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh
36
37/// @ingroup tools_background
38/// \class GridMedianBackgroundEstimator
39///
40/// Background Estimator based on the median pt/area of a set of grid
41/// cells.
42///
43/// Description of the method:
44/// This background estimator works by projecting the event onto a
45/// grid in rapidity and azimuth. In each grid cell, the scalar pt
46/// sum of the particles in the cell is computed. The background
47/// density is then estimated by the median of (scalar pt sum/cell
48/// area) for all cells.
49///
50/// Parameters:
51/// The class takes 2 arguments: the absolute rapidity extent of the
52/// cells and the size of the grid cells. Note that the size of the cell
53/// will be adjusted in azimuth to satisfy the 2pi periodicity and
54/// in rapidity to match the requested rapidity extent.
55///
56/// Rescaling:
57/// It is possible to use a rescaling profile. In this case, the
58/// profile needs to be set before setting the particles and it will
59/// be applied to each particle (i.e. not to each cell).
60/// Note also that in this case one needs to call rho(jet) instead of
61/// rho() [Without rescaling, they are identical]
62///
63class GridMedianBackgroundEstimator : public BackgroundEstimatorBase {
64public:
65 /// @name constructors and destructors
66 //\{
67 //----------------------------------------------------------------
68 /// \param ymax maximal absolute rapidity extent of the grid
69 /// \param requested_grid_spacing size of the grid cell. The
70 /// "real" cell size could differ due e.g. to the 2pi
71 /// periodicity in azimuthal angle (size, not area)
72 GridMedianBackgroundEstimator(double ymax, double requested_grid_spacing) :
73 _ymin(-ymax), _ymax(ymax),
74 _requested_grid_spacing(requested_grid_spacing),
75 _has_particles(false){setup_grid();}
76 //\}
77
78
79 /// @name setting a new event
80 //\{
81 //----------------------------------------------------------------
82
83 /// tell the background estimator that it has a new event, composed
84 /// of the specified particles.
85 void set_particles(const std::vector<PseudoJet> & particles);
86
87 //\}
88
89 /// @name retrieving fundamental information
90 //\{
91 //----------------------------------------------------------------
92
93 /// returns rho, the median background density per unit area
94 double rho() const;
95
96 /// returns sigma, the background fluctuations per unit area; must be
97 /// multipled by sqrt(area) to get fluctuations for a region of a
98 /// given area.
99 double sigma() const;
100
101 /// returns rho, the background density per unit area, locally at the
102 /// position of a given jet. Note that this is not const, because a
103 /// user may then wish to query other aspects of the background that
104 /// could depend on the position of the jet last used for a rho(jet)
105 /// determination.
106 double rho(const PseudoJet & jet);
107
108 /// returns sigma, the background fluctuations per unit area, locally at
109 /// the position of a given jet. As for rho(jet), it is non-const.
110 double sigma(const PseudoJet & jet);
111
112 /// returns true if this background estimator has support for
113 /// determination of sigma
114 bool has_sigma() {return true;}
115
116 /// returns the area of the grid cells (all identical, but
117 /// referred to as "mean" area for uniformity with JetMedianBGE).
118 double mean_area() const {return _cell_area;}
119 //\}
120
121 /// @name configuring the behaviour
122 //\{
123 //----------------------------------------------------------------
124
125 /// Set a pointer to a class that calculates the rescaling factor as
126 /// a function of the jet (position). Note that the rescaling factor
127 /// is used both in the determination of the "global" rho (the pt/A
128 /// of each jet is divided by this factor) and when asking for a
129 /// local rho (the result is multiplied by this factor).
130 ///
131 /// The BackgroundRescalingYPolynomial class can be used to get a
132 /// rescaling that depends just on rapidity.
133 ///
134 /// Note that this has to be called BEFORE any attempt to do an
135 /// actual computation
136 virtual void set_rescaling_class(const FunctionOfPseudoJet<double> * rescaling_class);
137
138 //\}
139
140 /// @name description
141 //\{
142 //----------------------------------------------------------------
143
144 /// returns a textual description of the background estimator
145 std::string description() const;
146
147 //\}
148
149
150private:
151 /// configure the grid
152 void setup_grid();
153
154 /// retrieve the grid cell index for a given PseudoJet
155 int igrid(const PseudoJet & p) const;
156
157 /// verify that particles have been set and throw an error if not
158 void verify_particles_set() const;
159
160 // information about the grid
161 double _ymin, _ymax, _dy, _dphi, _requested_grid_spacing, _cell_area;
162 int _ny, _nphi, _ntotal;
163
164 // information abotu the event
165 std::vector<double> _scalar_pt;
166 bool _has_particles;
167
168 // various warnings to let people aware of potential dangers
169 LimitedWarning _warning_rho_of_jet;
170 LimitedWarning _warning_rescaling;
171};
172
173FASTJET_END_NAMESPACE // defined in fastjet/internal/base.hh
174
175#endif // __GRID_MEDIAN_BACKGROUND_ESTIMATOR_HH__
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