GhostedAreaSpec.hh

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// Copyright (c) 2005-2024, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
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#ifndef __FASTJET_GHOSTEDAREASPEC_HH__
#define __FASTJET_GHOSTEDAREASPEC_HH__
 
#include<vector>
#include<string>
#include "fastjet/PseudoJet.hh"
#include "fastjet/internal/BasicRandom.hh"
#include "fastjet/Selector.hh"
#include "fastjet/LimitedWarning.hh"
#include "fastjet/internal/deprecated.hh"
#include "fastjet/SharedPtr.hh"
 
// 
#define STATIC_GENERATOR 1
 
FASTJET_BEGIN_NAMESPACE      // defined in fastjet/internal/base.hh
 
/// namespace to hold default parameters for the active area spec
namespace gas {
  const double def_ghost_maxrap  = 6.0;
  const int    def_repeat        = 1;
  const double def_ghost_area    = 0.01;
  const double def_grid_scatter  = 1.0;
  const double def_pt_scatter    = 0.1;
  const double def_mean_ghost_pt = 1e-100;
}
 
//----------------------------------------------------------------------
/// @ingroup area_classes
/// \class GhostedAreaSpec
/// Parameters to configure the computation of jet areas using ghosts
///
/// Class that defines the parameters that go into the measurement
/// of active jet areas.
///
/// Notes about thread-safety.
/// --------------------------
///
/// Ghosts are generated randomly, using by default a static random
/// number generator.
///
/// By default, we will lock the number generator during the period
/// over which we generate the required random numbers.  The procedure
/// will keep track of the seeds that have been used to generate a
/// particular set of ghosts and, ultimately, these seeds will be
/// made available from ClusterSequenceArea via
///
///   ClusterSequenceArea::area_def().ghost_spec().get_last_seed(vector<int>);
///
/// To use user-specified seeds in a thread-safe way, the end-user
/// should use
///
///   ClusterSequenceArea csa(particles, jet_def,
///                           area_def.with_fixed_seed(user_defined_seed));
///
/// or explicitly make a copy of the AreaDefinition before doing
/// the clustering:
///
///   AreaDefinition local_area_def
///     = area_def.with_fixed_seed(user_defined_seed);
///   ClusterSequenceArea csa(particles, jet_def, area_def,local_area_def);
///
/// This will use a local random generator to compute the ghosts (in
/// particular, it will not affect the static global generator)
///
/// Note that each clustering done with the GhostedAreaSpec obtained
/// through area_def.with_seed(user_defined_seed) will use exactly the
/// same set of ghosts.  Using
/// area_def.with_fixed_seed(user_defined_seed), with an empty vector
/// passed as argument, will return to using the common static random
/// generator.
class GhostedAreaSpec {
public:
  /// default constructor
  GhostedAreaSpec():
    _ghost_maxrap (gas::def_ghost_maxrap), 
    _ghost_rap_offset(0.0),
    _repeat       (gas::def_repeat), 
    _ghost_area   (gas::def_ghost_area), 
    _grid_scatter (gas::def_grid_scatter), 
    _pt_scatter   (gas::def_pt_scatter), 
    _mean_ghost_pt(gas::def_mean_ghost_pt),
    _fj2_placement(false),
    _user_random_generator(){_initialize();}
  
  /// explicit constructor
  ///
  /// It takes as parameters the maximal (abs) rapidity for the ghosts
  /// and an optional user-specified random number generator.
  ///
  /// For the latter, ownership is transferred to the GhostedAreaSpec
  /// class (i.e. it is stored internally as a shared pointer)
  explicit GhostedAreaSpec(double ghost_maxrap_in, 
                           BasicRandom<double> *user_random_generator): 
    _ghost_maxrap(ghost_maxrap_in), 
    _ghost_rap_offset(0.0),
    _repeat       (gas::def_repeat), 
    _ghost_area   (gas::def_ghost_area), 
    _grid_scatter (gas::def_grid_scatter), 
    _pt_scatter   (gas::def_pt_scatter), 
    _mean_ghost_pt(gas::def_mean_ghost_pt),
    _fj2_placement(false),
    _user_random_generator(user_random_generator) {_initialize();}
 
  /// explicit constructor
  explicit GhostedAreaSpec(double ghost_maxrap_in, 
                           int    repeat_in        = gas::def_repeat,
                           double ghost_area_in    = gas::def_ghost_area,   
                           double grid_scatter_in  = gas::def_grid_scatter, 
                           double pt_scatter_in    = gas::def_pt_scatter,   
                           double mean_ghost_pt_in = gas::def_mean_ghost_pt,
                           BasicRandom<double> *user_random_generator=NULL): 
    _ghost_maxrap(ghost_maxrap_in), 
    _ghost_rap_offset(0.0),
    _repeat(repeat_in), 
    _ghost_area(ghost_area_in), 
    _grid_scatter(grid_scatter_in),  
    _pt_scatter(pt_scatter_in), 
    _mean_ghost_pt(mean_ghost_pt_in),
    _fj2_placement(false),
    _user_random_generator(user_random_generator) {_initialize();}
 
  /// explicit constructor
  explicit GhostedAreaSpec(double ghost_minrap_in, 
                           double ghost_maxrap_in, 
                           int    repeat_in        = gas::def_repeat,
                           double ghost_area_in    = gas::def_ghost_area,   
                           double grid_scatter_in  = gas::def_grid_scatter, 
                           double pt_scatter_in    = gas::def_pt_scatter,   
                           double mean_ghost_pt_in = gas::def_mean_ghost_pt,
                           BasicRandom<double> *user_random_generator=NULL): 
    _ghost_maxrap    (0.5*(ghost_maxrap_in - ghost_minrap_in)), 
    _ghost_rap_offset(0.5*(ghost_maxrap_in + ghost_minrap_in)),
    _repeat(repeat_in), 
    _ghost_area(ghost_area_in), 
    _grid_scatter(grid_scatter_in),  
    _pt_scatter(pt_scatter_in), 
    _mean_ghost_pt(mean_ghost_pt_in),
    _fj2_placement(false),
    _user_random_generator(user_random_generator) {_initialize();}
 
 
  /// constructor based on a Selector
  explicit GhostedAreaSpec(const Selector & selector,
                           int    repeat_in        = gas::def_repeat,
                           double ghost_area_in    = gas::def_ghost_area,   
                           double grid_scatter_in  = gas::def_grid_scatter, 
                           double pt_scatter_in    = gas::def_pt_scatter,   
                           double mean_ghost_pt_in = gas::def_mean_ghost_pt,
                           BasicRandom<double> *user_random_generator=NULL);
 
 
  /// does the initialization of actual ghost parameters
  void _initialize();
 
  // for accessing values set by the user
  inline double ghost_rapmax () const {return _ghost_maxrap;}
  inline double ghost_maxrap () const {return _ghost_maxrap;}
  inline double ghost_etamax () const {return _ghost_maxrap;}
  inline double ghost_maxeta () const {return _ghost_maxrap;}
  inline double ghost_area   () const {return _ghost_area   ;}
  inline double grid_scatter () const {return _grid_scatter;}
  inline double pt_scatter   () const {return _pt_scatter  ;}
  inline double mean_ghost_pt() const {return _mean_ghost_pt  ;}
  inline int    repeat       () const {return _repeat      ;}
  inline bool   fj2_placement() const {return _fj2_placement;}
 
  inline double kt_scatter   () const {return _pt_scatter  ;}
  inline double mean_ghost_kt() const {return _mean_ghost_pt  ;}
 
  // for accessing values 
  inline double actual_ghost_area() const {return _actual_ghost_area;}
  inline int    n_ghosts()          const {return _n_ghosts;}
 
  // when explicitly modifying values, sometimes call the initializer
  inline void set_ghost_area   (double val) {_ghost_area    = val; _initialize();}
  inline void set_ghost_rapmax (double val) {_ghost_maxrap = val; _initialize();}
  inline void set_ghost_maxrap (double val) {_ghost_maxrap = val; _initialize();}
  inline void set_ghost_etamax (double val) {_ghost_maxrap = val; _initialize();}
  inline void set_ghost_maxeta (double val) {_ghost_maxrap = val; _initialize();}
  inline void set_grid_scatter (double val) {_grid_scatter   = val; }
  inline void set_pt_scatter   (double val) {_pt_scatter     = val; }
  inline void set_mean_ghost_pt(double val) {_mean_ghost_pt  = val; }
  inline void set_repeat       (int    val) {_repeat         = val; }
 
  inline void set_kt_scatter   (double val) {_pt_scatter     = val; }
  inline void set_mean_ghost_kt(double val) {_mean_ghost_pt  = val; }
 
  /// if val is true, set ghost placement as it was in FastJet 2.X. The
  /// main differences between FJ2 and FJ3 ghost placement are
  ///
  ///  - in FJ2 the rapidity spacing was
  ///    ceil((maxrap-minrap)/sqrt(area)), while in FJ3 it is
  ///    int((maxrap-minrap)/sqrt(area) + 0.5) [similarly for phi].
  ///    The FJ3 option offers more stability when trying to specify a
  ///    spacing that exactly fits the extent.
  ///
  /// - in FJ2, the ghosts are placed at the corners of grid cells
  ///   (i.e. extending up to maxrap), while in FJ3 they are placed at
  ///   the centres of grid cells (i.e. extending roughly up to
  ///   maxrap-sqrt(area)). The FJ2 behaviour effectively skews the
  ///   total area coverage when maxrap is small, by an amount
  ///   sqrt(area)/(2*maxrap).
  ///
  /// FJ2 placement is now deprecated.
  FASTJET_DEPRECATED_MSG("This is deprecated since we strongly recommend use of the new ghost placement instead",
  void set_fj2_placement(bool  val));
 
  /// return nphi (ghosts layed out (-nrap, 0..nphi-1), (-nrap+1,0..nphi-1),
  /// ... (nrap,0..nphi-1)
  inline int nphi() const {return _nphi;}
  inline int nrap() const {return _nrap;}
 
  /// get all relevant information about the status of the 
  /// random number generator, so that it can be reset subsequently
  /// with set_random_status.
  ///
  /// 
  inline void get_random_status(std::vector<int> & __iseed) const {
    if (_user_random_generator){
      _user_random_generator->get_status(__iseed);
    } else {
      _random_generator.get_status(__iseed);
    }
  }
 
  /// set the status of the random number generator, as obtained
  /// previously with get_random_status. Note that the random
  /// generator is a static member of the class, i.e. common to all
  /// instances of the class --- so if you modify the random for this
  /// instance, you modify it for all instances.
  inline void set_random_status(const std::vector<int> & __iseed) {
    if (_user_random_generator){
      _user_random_generator->set_status(__iseed);
    } else {
      _random_generator.set_status(__iseed);
    }
  }
 
  /// allows to return a copy of this GhostedAreaSpec with a local set
  /// of seeds
  GhostedAreaSpec with_fixed_seed(const std::vector<int> & __iseed) const {
    GhostedAreaSpec new_spec = (*this);
    new_spec._fixed_seed = __iseed;
    return new_spec;
  }
  
  /// returns the current fixed seed
  void get_fixed_seed(std::vector<int> & __iseed) const {
    __iseed = _fixed_seed;
  }
  
  /// allows the user to get the seed that was used at the start of the
  /// last generation of ghosts.
  ///
  /// This should typically be access through the area definition held
  /// by the ClusterSequenceArea, because the CSA class takes a copy of the
  /// AreaDefinition and it is that copy that stored the 
  void get_last_seed(std::vector<int> & __iseed) const {
    if (_repeat > 1) _warn_fixed_last_seeds_nrepeat_gt_1
                      .warn("Using fixed seeds (or accessing last used seeds) not sensible with repeat>1");
    __iseed = _last_used_seed;
  } 
 
  inline void checkpoint_random() {get_random_status(_random_checkpoint);}
  inline void restore_checkpoint_random() {set_random_status(_random_checkpoint);}
 
  /// for a summary
  std::string description() const;
 
  /// push a set of ghost 4-momenta onto the back of the vector of
  /// PseudoJets
  void add_ghosts(std::vector<PseudoJet> & ) const;
 
  /// very deprecated public access to a random number 
  /// from the internal generator
  inline double random_at_own_risk() const {return _our_rand();}
  /// very deprecated public access to the generator itself
  inline BasicRandom<double> & generator_at_own_risk() const {
    return _user_random_generator ? *_user_random_generator : _random_generator;}
  /// access to the user-defined random-number generator. Will be empty if not set.
  inline SharedPtr<BasicRandom<double> > & user_random_generator_at_own_risk(){
    return _user_random_generator;}
 
private:
  
  // quantities that determine nature and distribution of ghosts
  double _ghost_maxrap;
  double _ghost_rap_offset;
  int    _repeat      ;
  double _ghost_area   ;  
  double _grid_scatter;
  double _pt_scatter  ;
  double _mean_ghost_pt;
  bool   _fj2_placement;
 
  Selector _selector;
 
  // derived quantities
  double _actual_ghost_area, _dphi, _drap;
  int    _n_ghosts, _nphi, _nrap;
 
 
  std::vector<int> _random_checkpoint;
 
  // optional fixed seeds
  std::vector<int> _fixed_seed;
 
  // access to the seeds used the very last time
  mutable std::vector<int> _last_used_seed;
  
  // in order to keep thread-safety, have an independent random
  // generator for each thread
  //
  // 2015-09-24: thread_local is not supported by Apple's version of
  // clang! So we'll rely on something different here (see comment at
  // the top of the class)
  //#ifdef FASTJET_HAVE_LIMITED_THREAD_SAFETY
  //  static thread_local BasicRandom<double> _random_generator;
  //#else
  static BasicRandom<double> _random_generator;
  //#endif    
  //mutable BasicRandom<double> _random_generator;
 
  /// a set of seeds as defined by the end-user
  std::vector<int> _user_defined_seeds;
 
  // allow for a user-defined random generator
  SharedPtr<BasicRandom<double> > _user_random_generator;
  
  static LimitedWarning _warn_fj2_placement_deprecated;
  static LimitedWarning _warn_fixed_last_seeds_nrepeat_gt_1;
 
  inline double _our_rand() const {
    return _user_random_generator ? (*_user_random_generator)() : _random_generator();}
 
  inline void _our_rand(unsigned int npoints, double *pointer,
                        std::vector<int> & used_init_seed) const {
    return _user_random_generator
      ? (*_user_random_generator)(npoints, pointer, used_init_seed)
      : _random_generator(npoints, pointer, used_init_seed);
  }
  
};
 
/// just provide a typedef for backwards compatibility with programs
/// based on versions 2.0 and 2.1 of fastjet. Since there is no
/// easy way of telling people this is deprecated at compile or run
/// time, we should be careful before removing this in the future.
typedef GhostedAreaSpec ActiveAreaSpec;
 
 
FASTJET_END_NAMESPACE
 
#endif // __FASTJET_GHOSTEDAREASPEC_HH__