1 | #ifndef __FASTJET_BACKGROUND_ESTIMATOR_HH__ |
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2 | #define __FASTJET_BACKGROUND_ESTIMATOR_HH__ |
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3 | |
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4 | //STARTHEADER |
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5 | // $Id: JetMedianBackgroundEstimator.hh 2689 2011-11-14 14:51:06Z soyez $ |
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6 | // |
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7 | // Copyright (c) 2005-2011, Matteo Cacciari, Gavin P. Salam and Gregory Soyez |
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8 | // |
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9 | //---------------------------------------------------------------------- |
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10 | // This file is part of FastJet. |
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11 | // |
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12 | // FastJet is free software; you can redistribute it and/or modify |
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13 | // it under the terms of the GNU General Public License as published by |
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14 | // the Free Software Foundation; either version 2 of the License, or |
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15 | // (at your option) any later version. |
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16 | // |
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17 | // The algorithms that underlie FastJet have required considerable |
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18 | // development and are described in hep-ph/0512210. If you use |
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19 | // FastJet as part of work towards a scientific publication, please |
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20 | // include a citation to the FastJet paper. |
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21 | // |
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22 | // FastJet is distributed in the hope that it will be useful, |
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23 | // but WITHOUT ANY WARRANTY; without even the implied warranty of |
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24 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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25 | // GNU General Public License for more details. |
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26 | // |
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27 | // You should have received a copy of the GNU General Public License |
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28 | // along with FastJet. If not, see <http://www.gnu.org/licenses/>. |
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29 | //---------------------------------------------------------------------- |
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30 | //ENDHEADER |
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31 | |
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32 | #include <fastjet/ClusterSequenceAreaBase.hh> |
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33 | #include <fastjet/AreaDefinition.hh> |
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34 | #include <fastjet/FunctionOfPseudoJet.hh> |
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35 | #include <fastjet/Selector.hh> |
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36 | #include <fastjet/tools/BackgroundEstimatorBase.hh> |
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37 | #include <iostream> |
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38 | |
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39 | FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh |
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40 | |
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41 | |
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42 | /// @ingroup tools_background |
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43 | /// \class JetMedianBackgroundEstimator |
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44 | /// |
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45 | /// Class to estimate the pt density of the background per unit area, |
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46 | /// using the median of the distribution of pt/area from jets that |
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47 | /// pass some selection criterion. |
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48 | /// |
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49 | /// Events are passed either in the form of the event particles (in |
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50 | /// which they're clustered by the class), a ClusterSequenceArea (in |
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51 | /// which case the jets used are those returned by "inclusive_jets()") |
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52 | /// or directly as a set of jets. |
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53 | /// |
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54 | /// The selection criterion is typically a geometrical one (e.g. all |
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55 | /// jets with |y|<2) sometimes supplemented with some kinematical |
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56 | /// restriction (e.g. exclusion of the two hardest jets). It is passed |
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57 | /// to the class through a Selector. |
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58 | /// |
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59 | /// Beware: |
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60 | /// by default, to correctly handle partially empty events, the |
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61 | /// class attempts to calculate an "empty area", based |
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62 | /// (schematically) on |
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63 | /// |
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64 | /// range.total_area() - sum_{jets_in_range} jets.area() |
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65 | /// |
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66 | /// For ranges with small areas, this can be inaccurate (particularly |
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67 | /// relevant in dense events where empty_area should be zero and ends |
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68 | /// up not being zero). |
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69 | /// |
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70 | /// This calculation of empty area can be avoided if a |
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71 | /// ClusterSequenceArea class with explicit ghosts |
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72 | /// (ActiveAreaExplicitGhosts) is used. This is _recommended_ |
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73 | /// unless speed requirements cause you to use Voronoi areas. For |
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74 | /// speedy background estimation you could also consider using |
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75 | /// GridMedianBackgroundEstimator. |
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76 | /// |
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77 | /// |
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78 | class JetMedianBackgroundEstimator : public BackgroundEstimatorBase { |
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79 | public: |
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80 | /// @name constructors and destructors |
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81 | //\{ |
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82 | //---------------------------------------------------------------- |
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83 | /// Constructor that sets the rho range as well as the jet |
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84 | /// definition and area definition to be used to cluster the |
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85 | /// particles. Prior to the estimation of rho, one has to provide |
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86 | /// the particles to cluster using set_particles(...) |
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87 | /// |
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88 | /// \param rho_range the Selector specifying which jets will be considered |
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89 | /// \param jet_def the jet definition to use for the clustering |
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90 | /// \param area_def the area definition to use for the clustering |
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91 | JetMedianBackgroundEstimator(const Selector &rho_range, |
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92 | const JetDefinition &jet_def, |
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93 | const AreaDefinition &area_def); |
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94 | |
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95 | /// ctor from a ClusterSequenceAreaBase with area |
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96 | /// |
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97 | /// \param rho_range the Selector specifying which jets will be considered |
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98 | /// \param csa the ClusterSequenceArea to use |
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99 | /// |
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100 | /// Pre-conditions: |
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101 | /// - one should be able to estimate the "empty area" (i.e. the area |
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102 | /// not occupied by jets). This is feasible if at least one of the following |
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103 | /// conditions is satisfied: |
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104 | /// ( i) the ClusterSequence has explicit ghosts |
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105 | /// (ii) the range has a computable area. |
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106 | /// - the jet algorithm must be suited for median computation |
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107 | /// (otherwise a warning will be issues) |
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108 | /// |
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109 | /// Note that selectors with e.g. hardest-jets exclusion do not have |
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110 | /// a well-defined area. For this reasons, it is STRONGLY advised to |
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111 | /// use an area with explicit ghosts. |
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112 | JetMedianBackgroundEstimator(const Selector &rho_range, |
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113 | const ClusterSequenceAreaBase &csa); |
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114 | |
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115 | |
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116 | /// Default constructor that optionally sets the rho range. The |
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117 | /// configuration must be done later calling |
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118 | /// set_cluster_sequence(...) or set_jets(...). |
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119 | /// |
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120 | /// \param rho_range the Selector specifying which jets will be considered |
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121 | /// |
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122 | JetMedianBackgroundEstimator(const Selector &rho_range = SelectorIdentity()) |
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123 | : _rho_range(rho_range), _jet_def(JetDefinition()) { reset(); } |
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124 | |
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125 | |
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126 | /// default dtor |
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127 | ~JetMedianBackgroundEstimator(){} |
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128 | |
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129 | //\} |
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130 | |
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131 | |
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132 | /// @name setting a new event |
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133 | //\{ |
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134 | //---------------------------------------------------------------- |
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135 | |
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136 | /// tell the background estimator that it has a new event, composed |
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137 | /// of the specified particles. |
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138 | virtual void set_particles(const std::vector<PseudoJet> & particles); |
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139 | |
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140 | /// (re)set the cluster sequence (with area support) to be used by |
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141 | /// future calls to rho() etc. |
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142 | /// |
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143 | /// \param csa the cluster sequence area |
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144 | /// |
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145 | /// Pre-conditions: |
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146 | /// - one should be able to estimate the "empty area" (i.e. the area |
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147 | /// not occupied by jets). This is feasible if at least one of the following |
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148 | /// conditions is satisfied: |
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149 | /// ( i) the ClusterSequence has explicit ghosts |
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150 | /// (ii) the range selected has a computable area. |
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151 | /// - the jet algorithm must be suited for median computation |
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152 | /// (otherwise a warning will be issues) |
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153 | /// |
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154 | /// Note that selectors with e.g. hardest-jets exclusion do not have |
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155 | /// a well-defined area. For this reasons, it is STRONGLY advised to |
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156 | /// use an area with explicit ghosts. |
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157 | void set_cluster_sequence(const ClusterSequenceAreaBase & csa); |
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158 | |
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159 | /// (re)set the jets (which must have area support) to be used by future |
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160 | /// calls to rho() etc.; for the conditions that must be satisfied |
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161 | /// by the jets, see the Constructor that takes jets. |
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162 | void set_jets(const std::vector<PseudoJet> &jets); |
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163 | |
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164 | /// (re)set the selector to be used for future calls to rho() etc. |
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165 | void set_selector(const Selector & rho_range_selector) { |
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166 | _rho_range = rho_range_selector; |
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167 | _uptodate = false; |
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168 | } |
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169 | |
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170 | //\} |
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171 | |
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172 | |
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173 | /// @name retrieving fundamental information |
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174 | //\{ |
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175 | //---------------------------------------------------------------- |
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176 | |
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177 | /// get rho, the median background density per unit area |
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178 | double rho() const; |
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179 | |
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180 | /// get sigma, the background fluctuations per unit area |
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181 | double sigma() const; |
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182 | |
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183 | /// get rho, the median background density per unit area, locally at |
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184 | /// the position of a given jet. |
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185 | /// |
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186 | /// If the Selector associated with the range takes a reference jet |
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187 | /// (i.e. is relocatable), then for subsequent operations the |
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188 | /// Selector has that jet set as its reference. |
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189 | double rho(const PseudoJet & jet); |
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190 | |
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191 | /// get sigma, the background fluctuations per unit area, |
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192 | /// locally at the position of a given jet. |
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193 | /// |
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194 | /// If the Selector associated with the range takes a reference jet |
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195 | /// (i.e. is relocatable), then for subsequent operations the |
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196 | /// Selector has that jet set as its reference. |
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197 | double sigma(const PseudoJet &jet); |
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198 | |
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199 | /// returns true if this background estimator has support for |
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200 | /// determination of sigma |
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201 | virtual bool has_sigma() {return true;} |
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202 | |
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203 | //\} |
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204 | |
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205 | /// @name retrieving additional useful information |
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206 | //\{ |
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207 | //---------------------------------------------------------------- |
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208 | /// Returns the mean area of the jets used to actually compute the |
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209 | /// background properties in the last call of rho() or sigma() |
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210 | double mean_area() const{ |
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211 | _recompute_if_needed(); |
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212 | return _mean_area; |
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213 | } |
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214 | |
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215 | /// returns the number of jets used to actually compute the |
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216 | /// background properties in the last call of rho() or sigma() |
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217 | unsigned int n_jets_used() const{ |
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218 | _recompute_if_needed(); |
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219 | return _n_jets_used; |
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220 | } |
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221 | |
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222 | /// Returns the estimate of the area (within the range defined by |
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223 | /// the selector) that is not occupied by jets. The value is that |
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224 | /// for the last call of rho() or sigma() |
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225 | /// |
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226 | /// The answer is defined to be zero if the area calculation |
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227 | /// involved explicit ghosts; if the area calculation was an active |
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228 | /// area, then use is made of the active area's internal list of |
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229 | /// pure ghost jets (taking those that pass the selector); otherwise |
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230 | /// it is based on the difference between the selector's total area |
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231 | /// and the area of the jets that pass the selector. |
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232 | /// |
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233 | /// The result here is just the cached result of the corresponding |
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234 | /// call to the ClusterSequenceAreaBase function. |
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235 | double empty_area() const{ |
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236 | _recompute_if_needed(); |
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237 | return _empty_area; |
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238 | } |
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239 | |
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240 | /// Returns the number of empty jets used when computing the |
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241 | /// background properties. The value is that for the last call of |
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242 | /// rho() or sigma(). |
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243 | /// |
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244 | /// If the area has explicit ghosts the result is zero; for active |
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245 | /// areas it is the number of internal pure ghost jets that pass the |
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246 | /// selector; otherwise it is deduced from the empty area, divided by |
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247 | /// \f$ 0.55 \pi R^2 \f$ (the average pure-ghost-jet area). |
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248 | /// |
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249 | /// The result here is just the cached result of the corresponding |
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250 | /// call to the ClusterSequenceAreaBase function. |
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251 | double n_empty_jets() const{ |
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252 | _recompute_if_needed(); |
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253 | return _n_empty_jets; |
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254 | } |
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255 | |
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256 | //} |
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257 | |
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258 | |
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259 | /// @name configuring behaviour |
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260 | //\{ |
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261 | //---------------------------------------------------------------- |
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262 | |
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263 | /// Resets the class to its default state, including the choice to |
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264 | /// use 4-vector areas. |
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265 | /// |
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266 | void reset(); |
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267 | |
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268 | /// By default when calculating pt/Area for a jet, it is the |
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269 | /// transverse component of the 4-vector area that is used in the ratiof \f$p_t/A\f$. |
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270 | /// Calling this function with a "false" argument causes the scalar area to |
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271 | /// be used instead. |
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272 | /// |
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273 | /// While the difference between the two choices is usually small, |
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274 | /// for high-precision work it is usually the 4-vector area that is |
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275 | /// to be preferred. |
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276 | /// |
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277 | /// \param use_it whether one uses the 4-vector area or not (true by default) |
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278 | void set_use_area_4vector(bool use_it = true){ |
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279 | _use_area_4vector = use_it; |
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280 | _uptodate = false; |
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281 | } |
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282 | |
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283 | /// check if the estimator uses the 4-vector area or the scalar area |
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284 | bool use_area_4vector() const{ return _use_area_4vector;} |
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285 | |
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286 | /// The FastJet v2.X sigma calculation had a small spurious offset |
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287 | /// in the limit of a small number of jets. This is fixed by default |
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288 | /// in versions 3 upwards. The old behaviour can be obtained with a |
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289 | /// call to this function. |
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290 | void set_provide_fj2_sigma(bool provide_fj2_sigma = true) { |
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291 | _provide_fj2_sigma = provide_fj2_sigma; |
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292 | _uptodate = false; |
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293 | } |
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294 | |
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295 | /// Set a pointer to a class that calculates the quantity whose |
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296 | /// median will be calculated; if the pointer is null then pt/area |
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297 | /// is used (as occurs also if this function is not called). |
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298 | /// |
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299 | /// Note that this is still <i>preliminary</i> in FastJet 3.0 and |
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300 | /// that backward compatibility is not guaranteed in future releases |
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301 | /// of FastJet |
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302 | void set_jet_density_class(const FunctionOfPseudoJet<double> * jet_density_class); |
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303 | |
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304 | /// return the pointer to the jet density class |
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305 | const FunctionOfPseudoJet<double> * jet_density_class() const{ |
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306 | return _jet_density_class; |
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307 | } |
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308 | |
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309 | /// Set a pointer to a class that calculates the rescaling factor as |
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310 | /// a function of the jet (position). Note that the rescaling factor |
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311 | /// is used both in the determination of the "global" rho (the pt/A |
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312 | /// of each jet is divided by this factor) and when asking for a |
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313 | /// local rho (the result is multiplied by this factor). |
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314 | /// |
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315 | /// The BackgroundRescalingYPolynomial class can be used to get a |
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316 | /// rescaling that depends just on rapidity. |
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317 | virtual void set_rescaling_class(const FunctionOfPseudoJet<double> * rescaling_class_in) { |
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318 | BackgroundEstimatorBase::set_rescaling_class(rescaling_class_in); |
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319 | _uptodate = false; |
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320 | } |
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321 | |
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322 | //\} |
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323 | |
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324 | /// @name description |
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325 | //\{ |
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326 | //---------------------------------------------------------------- |
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327 | |
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328 | /// returns a textual description of the background estimator |
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329 | std::string description() const; |
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330 | |
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331 | //\} |
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332 | |
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333 | |
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334 | private: |
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335 | |
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336 | /// do the actual job |
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337 | void _compute() const; |
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338 | |
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339 | /// check if the properties need to be recomputed |
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340 | /// and do so if needed |
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341 | void _recompute_if_needed() const { |
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342 | if (!_uptodate) _compute(); |
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343 | _uptodate = true; |
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344 | } |
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345 | |
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346 | /// for estimation using a selector that takes a reference jet |
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347 | /// (i.e. a selector that can be relocated) this function allows one |
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348 | /// to set its position. |
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349 | /// |
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350 | /// Note that this HAS to be called before any attempt to compute |
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351 | /// the background properties. The call is, however, performed |
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352 | /// automatically by the functions rho(jet) and sigma(jet). |
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353 | void _recompute_if_needed(const PseudoJet &jet); |
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354 | |
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355 | /// check that the underlying structure is still alive |
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356 | /// throw an error otherwise |
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357 | void _check_csa_alive() const; |
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358 | |
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359 | /// check that the algorithm used for the clustering is adapted for |
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360 | /// background estimation (i.e. either kt or C/A) |
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361 | /// Issue a warning otherwise |
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362 | void _check_jet_alg_good_for_median() const; |
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363 | |
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364 | // the basic parameters of this class (passed through the variou ctors) |
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365 | Selector _rho_range; ///< range to compute the background in |
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366 | JetDefinition _jet_def; ///< the jet def to use for teh clustering |
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367 | AreaDefinition _area_def; ///< the area def to use for teh clustering |
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368 | std::vector<PseudoJet> _included_jets; ///< jets to be used |
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369 | |
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370 | // the tunable aprameters of the class |
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371 | bool _use_area_4vector; |
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372 | bool _provide_fj2_sigma; |
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373 | const FunctionOfPseudoJet<double> * _jet_density_class; |
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374 | //SharedPtr<BackgroundRescalingBase> _rescaling_class_sharedptr; |
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375 | |
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376 | // the actual results of the computation |
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377 | mutable double _rho; ///< background estimated density per unit area |
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378 | mutable double _sigma; ///< background estimated fluctuations |
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379 | mutable double _mean_area; ///< mean area of the jets used to estimate the background |
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380 | mutable unsigned int _n_jets_used; ///< number of jets used to estimate the background |
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381 | mutable double _n_empty_jets; ///< number of empty (pure-ghost) jets |
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382 | mutable double _empty_area; ///< the empty (pure-ghost/unclustered) area! |
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383 | |
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384 | // internal variables |
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385 | SharedPtr<PseudoJetStructureBase> _csi; ///< allows to check if _csa is still valid |
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386 | PseudoJet _current_reference; ///< current reference jet |
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387 | mutable bool _uptodate; ///< true when the background computation is up-to-date |
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388 | |
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389 | /// handle warning messages |
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390 | static LimitedWarning _warnings; |
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391 | static LimitedWarning _warnings_zero_area; |
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392 | static LimitedWarning _warnings_preliminary; |
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393 | }; |
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394 | |
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395 | |
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396 | |
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397 | |
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398 | //---------------------------------------------------------------------- |
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399 | /// @ingroup tools_background |
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400 | /// \class BackgroundJetPtDensity |
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401 | /// Class that implements pt/area_4vector.perp() for background estimation |
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402 | /// <i>(this is a preliminary class)</i>. |
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403 | class BackgroundJetPtDensity : public FunctionOfPseudoJet<double> { |
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404 | public: |
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405 | virtual double result(const PseudoJet & jet) const { |
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406 | return jet.perp() / jet.area_4vector().perp(); |
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407 | } |
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408 | virtual std::string description() const {return "BackgroundJetPtDensity";} |
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409 | }; |
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410 | |
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411 | |
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412 | //---------------------------------------------------------------------- |
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413 | /// @ingroup tools_background |
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414 | /// \class BackgroundJetScalarPtDensity |
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415 | /// Class that implements (scalar pt sum of jet)/(scalar area of jet) |
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416 | /// for background estimation <i>(this is a preliminary class)</i>. |
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417 | /// |
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418 | /// Optionally it can return a quantity based on the sum of pt^n, |
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419 | /// e.g. for use in subtracting fragementation function moments. |
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420 | class BackgroundJetScalarPtDensity : public FunctionOfPseudoJet<double> { |
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421 | public: |
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422 | /// Default constructor provides background estimation with scalar pt sum |
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423 | BackgroundJetScalarPtDensity() : _pt_power(1) {} |
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424 | |
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425 | /// Constructor to provide background estimation based on |
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426 | /// \f$ sum_{i\in jet} p_{ti}^{n} \f$ |
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427 | BackgroundJetScalarPtDensity(double n) : _pt_power(n) {} |
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428 | |
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429 | virtual double result(const PseudoJet & jet) const; |
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430 | |
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431 | virtual std::string description() const {return "BackgroundScalarJetPtDensity";} |
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432 | |
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433 | private: |
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434 | double _pt_power; |
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435 | }; |
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436 | |
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437 | //---------------------------------------------------------------------- |
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438 | /// @ingroup tools_background |
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439 | /// \class BackgroundJetPtMDensity |
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440 | /// Class that implements |
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441 | /// \f$ \frac{1}{A} \sum_{i \in jet} (\sqrt{p_{ti}^2+m^2} - p_{ti}) \f$ |
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442 | /// for background estimation <i>(this is a preliminary class)</i>. |
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443 | /// |
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444 | /// |
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445 | /// This is useful for correcting jet masses in cases where the event |
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446 | /// involves massive particles. |
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447 | class BackgroundJetPtMDensity : public FunctionOfPseudoJet<double> { |
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448 | public: |
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449 | virtual double result(const PseudoJet & jet) const { |
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450 | std::vector<PseudoJet> constituents = jet.constituents(); |
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451 | double scalar_ptm = 0; |
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452 | for (unsigned i = 0; i < constituents.size(); i++) { |
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453 | scalar_ptm += constituents[i].mperp() - constituents[i].perp(); |
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454 | } |
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455 | return scalar_ptm / jet.area(); |
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456 | } |
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457 | |
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458 | virtual std::string description() const {return "BackgroundPtMDensity";} |
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459 | }; |
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460 | |
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461 | |
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462 | |
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463 | FASTJET_END_NAMESPACE |
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464 | |
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465 | #endif // __BACKGROUND_ESTIMATOR_HH__ |
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466 | |
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