fastjet/contrib/XConePlugin.hh

0001 //  Nsubjettiness Package
0002 //  Questions/Comments?  jthaler@jthaler.net
0003 //
0004 //  Copyright (c) 2011-14
0005 //  Jesse Thaler, Ken Van Tilburg, Christopher K. Vermilion, and TJ Wilkason
0006 //
0007 //  $Id: XConePlugin.hh 748 2014-10-02 06:13:28Z tjwilk $
0008 //----------------------------------------------------------------------
0009 // This file is part of FastJet contrib.
0010 //
0011 // It is free software; you can redistribute it and/or modify it under
0012 // the terms of the GNU General Public License as published by the
0013 // Free Software Foundation; either version 2 of the License, or (at
0014 // your option) any later version.
0015 //
0016 // It is distributed in the hope that it will be useful, but WITHOUT
0017 // ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
0018 // or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
0019 // License for more details.
0020 //
0021 // You should have received a copy of the GNU General Public License
0022 // along with this code. If not, see <http://www.gnu.org/licenses/>.
0023 //----------------------------------------------------------------------
0024
0025 #ifndef __FASTJET_CONTRIB_XCONEPLUGIN_HH__
0026 #define __FASTJET_CONTRIB_XCONEPLUGIN_HH__
0027
0028 #include <fastjet/config.h>
0029
0030 #include "NjettinessPlugin.hh"
0031
0032 #include "fastjet/ClusterSequence.hh"
0033 #include "fastjet/JetDefinition.hh"
0034
0035 #include <string>
0036 #include <climits>
0037
0038 FASTJET_BEGIN_NAMESPACE      // defined in fastjet/internal/base.hh
0039
0040
0041 namespace contrib {
0042
0043 ///------------------------------------------------------------------------
0044 /// \class XConePlugin
0045 /// \brief Implements the XCone Jet Algorithm
0046 /**
0047  * An exclusive jet finder that identifies N jets.  First N axes are found, then
0048  * particles are assigned to the nearest (approximte DeltaR) axis and for each axis the
0049  * corresponding jet is simply the four-momentum sum of these particles.
0050  *
0051  * The XConePlugin is based on NjettinessPlugin, but with sensible default
0052  * values for the AxesDefinition and MeasureDefinition.  There are three arguments
0053  *
0054  *   int N:       number of exclusive jets to be found
0055  *   double R0:   approximate jet radius
0056  *   double beta: determines style of jet finding with the recommended values being:
0057  *                beta = 2:  standard "mean" jets where jet momentum/axis align approximately.
0058  *                beta = 1:  recoil-free "median" variant where jet axis points at hardest cluster.
0059  *
0060  * The AxesDefinition is OnePass_GenET_GenKT_Axes, which uses a generalized kT
0061  * clustering algorithm matched to the beta value.
0062  *
0063  * The MeasureDefinition is the XConeMeasure, which is based on the
0064  * ConicalGeometric measure.
0065  */
0066 class XConePlugin : public NjettinessPlugin {
0067 public:
0068
0069    /// Constructor with N, R0, and beta as the options.  beta = 2.0 is the default
0070    /// All this does is use the NjettinessPlugin with OnePass_GenET_GenKT_Axes and the XConeMeasure.
0071    /// For more advanced usage, call NjettinessPlugin directly
0072    /// Note that the order of the R0 and beta values is reversed from the XConeMeasure to
0073    /// standard usage for Plugins.
0074    XConePlugin(int N, double R0, double beta = 2.0)
0075    : NjettinessPlugin(N,
0076                       OnePass_GenET_GenKT_Axes(calc_delta(beta), calc_power(beta), R0), // use recommended axes method only
0077                       XConeMeasure(beta, R0)  // use recommended XCone measure.
0078                       ),
0079    _N(N), _R0(R0), _beta(beta)
0080    {}
0081
0082    // The things that are required by base class.
0083    virtual std::string description () const;
0084    virtual double R() const {return _R0;}
0085
0086    // run_clustering is done by NjettinessPlugin
0087
0088    virtual ~XConePlugin() {}
0089
0090 private:
0091
0092    /// Static call used within the constructor to set the recommended delta value
0093    static double calc_delta(double beta) {
0094       double delta;
0095       if (beta > 1) delta = 1/(beta - 1);
0096       else delta = std::numeric_limits<int>::max(); // use winner take all
0097       return delta;
0098    }
0099
0100    /// Static call used within the constructor to set the recommended p value
0101    static double calc_power(double beta) {
0102       return (double) 1.0/beta;
0103    }
0104
0105    double _N;    ///< Number of desired jets
0106    double _R0;   ///< Jet radius
0107    double _beta; ///< Angular exponent (beta = 2.0 is dafault, beta = 1.0 is recoil-free)
0108
0109 public:
0110
0111 };
0112
0113
0114 /// \class PseudoXConePlugin
0115 /// \brief Implements a faster, non-optimal version of the XCone Jet Algorithm
0116 ///
0117 /// A "poor man's" version of XCone with no minimization step
0118 /// Right now, used just for testing purposes by the developers
0119 class PseudoXConePlugin : public NjettinessPlugin {
0120 public:
0121
0122    /// Constructor with N, R0, and beta as the options.  beta = 2.0 is the default
0123    /// All this does is use the NjettinessPlugin with GenET_GenKT_Axes and the XConeMeasure.
0124    PseudoXConePlugin(int N, double R0, double beta = 2.0)
0125    : NjettinessPlugin(N,
0126                       GenET_GenKT_Axes(calc_delta(beta), calc_power(beta), R0), // poor man's axes
0127                       XConeMeasure(beta, R0)  // use recommended XCone measure.
0128                       ),
0129    _N(N), _R0(R0), _beta(beta)
0130    {}
0131
0132    // The things that are required by base class.
0133    virtual std::string description () const;
0134    virtual double R() const {return _R0;}
0135
0136    // run_clustering is done by NjettinessPlugin
0137
0138    virtual ~PseudoXConePlugin() {}
0139
0140 private:
0141
0142    /// Static call used within the constructor to set the recommended delta value
0143    static double calc_delta(double beta) {
0144       double delta;
0145       if (beta > 1) delta = 1/(beta - 1);
0146       else delta = std::numeric_limits<int>::max(); // use winner take all
0147       return delta;
0148    }
0149
0150    /// Static call used within the constructor to set the recommended p value
0151    static double calc_power(double beta) {
0152       return (double) 1.0/beta;
0153    }
0154
0155    double _N;    ///< Number of desired jets
0156    double _R0;   ///< Jet radius
0157    double _beta; ///< Angular exponent (beta = 2.0 is dafault, beta = 1.0 is recoil-free)
0158
0159 public:
0160
0161 };
0162
0163
0164
0165 } // namespace contrib
0166
0167 FASTJET_END_NAMESPACE
0168
0169 #endif  // __FASTJET_CONTRIB_XConePlugin_HH__