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 #ifndef __GRID_MEDIAN_BACKGROUND_ESTIMATOR_HH__
 #define __GRID_MEDIAN_BACKGROUND_ESTIMATOR_HH__
 
 //FJSTARTHEADER
 // $Id$
 //
 // Copyright (c) 2005-2021, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
 //
 //----------------------------------------------------------------------
 // This file is part of FastJet.
 //
 //  FastJet is free software; you can redistribute it and/or modify
 //  it under the terms of the GNU General Public License as published by
 //  the Free Software Foundation; either version 2 of the License, or
 //  (at your option) any later version.
 //
 //  The algorithms that underlie FastJet have required considerable
 //  development. They are described in the original FastJet paper,
 //  hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use
 //  FastJet as part of work towards a scientific publication, please
 //  quote the version you use and include a citation to the manual and
 //  optionally also to hep-ph/0512210.
 //
 //  FastJet is distributed in the hope that it will be useful,
 //  but WITHOUT ANY WARRANTY; without even the implied warranty of
 //  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 //  GNU General Public License for more details.
 //
 //  You should have received a copy of the GNU General Public License
 //  along with FastJet. If not, see <http://www.gnu.org/licenses/>.
 //----------------------------------------------------------------------
 //FJENDHEADER
 
 
 #include "fastjet/tools/BackgroundEstimatorBase.hh"
 #include "fastjet/RectangularGrid.hh"
 
 
 FASTJET_BEGIN_NAMESPACE      // defined in fastjet/internal/base.hh
 
 /// @ingroup tools_background
 /// \class GridMedianBackgroundEstimator
 /// 
 /// Background Estimator based on the median pt/area of a set of grid
 /// cells. 
 ///
 /// Description of the method:
 ///   This background estimator works by projecting the event onto a
 ///   grid in rapidity and azimuth. In each grid cell, the scalar pt
 ///   sum of the particles in the cell is computed. The background
 ///   density is then estimated by the median of (scalar pt sum/cell
 ///   area) for all cells.
 ///
 /// Parameters:
 ///   The class takes 2 arguments: the absolute rapidity extent of the 
 ///   cells and the size of the grid cells. Note that the size of the cell
 ///   will be adjusted in azimuth to satisfy the 2pi periodicity and
 ///   in rapidity to match the requested rapidity extent.
 ///
 /// Rescaling:
 ///   It is possible to use a rescaling profile. In this case, the
 ///   profile needs to be set before setting the particles and it will
 ///   be applied to each particle (i.e. not to each cell). 
 ///   Note also that in this case one needs to call rho(jet) instead of
 ///   rho() [Without rescaling, they are identical]
 ///
 class GridMedianBackgroundEstimator : public BackgroundEstimatorBase
                                     , public RectangularGrid
 {
 
 public:
   /// @name  constructors and destructors
   //\{
   //----------------------------------------------------------------
   ///   \param ymax   maximal absolute rapidity extent of the grid
   ///   \param requested_grid_spacing   size of the grid cell. The
   ///            "real" cell size could differ due e.g. to the 2pi
   ///             periodicity in azimuthal angle (size, not area)
   GridMedianBackgroundEstimator(double ymax, double requested_grid_spacing) :
     RectangularGrid(ymax, requested_grid_spacing),
     _enable_rho_m(true) {} 
 
   //----------------------------------------------------------------
   /// Constructor based on a user's fully specified RectangularGrid
   GridMedianBackgroundEstimator(const RectangularGrid & grid) :
     RectangularGrid(grid), _enable_rho_m(true) {
     if (!RectangularGrid::is_initialised()) 
       throw Error("attempt to construct GridMedianBackgroundEstimator with uninitialised RectangularGrid");
   }    
 
   //---------------------------------------------------------------- 
   /// Constructor with the explicit parameters for the underlying
   /// RectangularGrid
   ///
   ///  \param rapmin         the minimum rapidity extent of the grid
   ///  \param rapmax         the maximum rapidity extent of the grid
   ///  \param drap           the grid spacing in rapidity
   ///  \param dphi           the grid spacing in azimuth
   ///  \param tile_selector  optional (geometric) selector to specify 
   ///                        which tiles are good; a tile is good if
   ///                        a massless 4-vector at the center of the tile passes
   ///                        the selection
   GridMedianBackgroundEstimator(double rapmin_in, double rapmax_in, double drap_in, double dphi_in,
                                 Selector tile_selector = Selector()) :
     RectangularGrid(rapmin_in, rapmax_in, drap_in, dphi_in, tile_selector), _enable_rho_m(true) {}
 
   //\}
 
 
   /// @name setting a new event
   //\{
   //----------------------------------------------------------------
 
   /// tell the background estimator that it has a new event, composed
   /// of the specified particles.
   void set_particles(const std::vector<PseudoJet> & particles) FASTJET_OVERRIDE;
 
   /// determine whether the automatic calculation of rho_m and sigma_m
   /// is enabled (by default true)
   void set_compute_rho_m(bool enable){ _enable_rho_m = enable; }
 
   //\}
 
   /// return a pointer to a copy of this BGE; the user is responsible
   /// for eventually deleting the resulting object.
   BackgroundEstimatorBase * copy() const FASTJET_OVERRIDE {
     return new GridMedianBackgroundEstimator(*this);
   };
 
 
 
   /// @name  retrieving fundamental information
   //\{
   //----------------------------------------------------------------
   /// get the full set of background properties
   BackgroundEstimate estimate() const FASTJET_OVERRIDE;
   
   /// get the full set of background properties for a given reference jet
   BackgroundEstimate estimate(const PseudoJet &jet) const FASTJET_OVERRIDE;
 
   /// returns rho, the median background density per unit area
   double rho() const FASTJET_OVERRIDE;
 
   /// returns sigma, the background fluctuations per unit area; must be
   /// multipled by sqrt(area) to get fluctuations for a region of a
   /// given area.
   double sigma() const FASTJET_OVERRIDE;
 
   /// returns rho, the background density per unit area, locally at the
   /// position of a given jet. Note that this is not const, because a
   /// user may then wish to query other aspects of the background that
   /// could depend on the position of the jet last used for a rho(jet)
   /// determination.
   double rho(const PseudoJet & jet) FASTJET_OVERRIDE;
 
   /// returns sigma, the background fluctuations per unit area, locally at
   /// the position of a given jet. As for rho(jet), it is non-const.
   double sigma(const PseudoJet & jet) FASTJET_OVERRIDE;
 
   /// returns true if this background estimator has support for
   /// determination of sigma
   bool has_sigma() const FASTJET_OVERRIDE {return true;}
 
   //-----------------------------------------------------------------
   /// Returns rho_m, the purely longitudinal, particle-mass-induced
   /// component of the background density per unit area
   double rho_m() const FASTJET_OVERRIDE;
 
   /// returns sigma_m, a measure of the fluctuations in the purely
   /// longitudinal, particle-mass-induced component of the background
   /// density per unit area; must be multipled by sqrt(area) to get
   /// fluctuations for a region of a given area.
   double sigma_m() const FASTJET_OVERRIDE;
 
   /// Returns rho_m locally at the jet position. As for rho(jet), it is non-const.
   double rho_m(const PseudoJet & jet) FASTJET_OVERRIDE;
 
   /// Returns sigma_m locally at the jet position. As for rho(jet), it is non-const.
   double sigma_m(const PseudoJet & jet) FASTJET_OVERRIDE;
 
   /// Returns true if this background estimator has support for
   /// determination of rho_m.
   ///
   /// Note that support for sigma_m is automatic if one has sigma and
   /// rho_m support.
   bool has_rho_m() const FASTJET_OVERRIDE {return _enable_rho_m;}
 
 
   /// returns the area of the grid cells (all identical, but
   /// referred to as "mean" area for uniformity with JetMedianBGE).
   double mean_area() const {return mean_tile_area();}
   //\}
 
   /// @name configuring the behaviour
   //\{
   //----------------------------------------------------------------
 
   /// Set a pointer to a class that calculates the rescaling factor as
   /// a function of the jet (position). Note that the rescaling factor
   /// is used both in the determination of the "global" rho (the pt/A
   /// of each jet is divided by this factor) and when asking for a
   /// local rho (the result is multiplied by this factor).
   ///
   /// The BackgroundRescalingYPolynomial class can be used to get a
   /// rescaling that depends just on rapidity.
   ///
   /// Note that this has to be called BEFORE any attempt to do an
   /// actual computation
   ///
   /// The same profile will be used for both pt and mt (this is
   /// probabaly a good approximation since the particle density
   /// changes is what dominates the rapidity profile)
   virtual void set_rescaling_class(const FunctionOfPseudoJet<double> * rescaling_class) FASTJET_OVERRIDE;
 
   //\}
 
   /// @name description
   //\{
   //----------------------------------------------------------------
 
   /// returns a textual description of the background estimator
   std::string description() const FASTJET_OVERRIDE;
 
   //\}
 
 
 private:
 
   /// verify that particles have been set and throw an error if not
   void verify_particles_set() const;
 
   // information about the event
   //std::vector<double> _scalar_pt;
   //double _rho, _sigma, _rho_m, _sigma_m;
   BackgroundEstimate _cached_estimate;
   //bool _has_particles;
   bool _enable_rho_m;
 
   // various warnings to inform people of potential dangers
   LimitedWarning _warning_rho_of_jet;
   LimitedWarning _warning_rescaling;
 };
 
 FASTJET_END_NAMESPACE        // defined in fastjet/internal/base.hh
 
 #endif // __GRID_MEDIAN_BACKGROUND_ESTIMATOR_HH__

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