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 // Copyright (c) 2005-2025, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
 //
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 // This file is part of FastJet.
 //
 //  FastJet is free software; you can redistribute it and/or modify
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 //  the Free Software Foundation; either version 2 of the License, or
 //  (at your option) any later version.
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 //  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
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 #include "fastjet/config.h"
 
 #ifndef DROP_CGAL // in case we do not have the code for CGAL
 
 #ifndef __FASTJET_DNNPLANE_HH__
 #define __FASTJET_DNNPLANE_HH__
 
 #include "fastjet/internal/Triangulation.hh"
 #include "fastjet/internal/DynamicNearestNeighbours.hh"
 
 FASTJET_BEGIN_NAMESPACE      // defined in fastjet/internal/base.hh
 
 
 /// \if internal_doc
 /// @ingroup internal
 /// \class DnnPlane
 /// class derived from DynamicNearestNeighbours that provides an
 /// implementation for the Euclidean plane
 ///
 /// This class that uses CGAL Delaunay triangulation for most of the
 /// work (it allows for easy and efficient removal and addition of
 /// points and circulation over a point's neighbours). The treatment
 /// of coincident points is not supported by CGAL and is implemented
 /// according to the method specified in
 /// issue-tracker/2012-02-CGAL-coincident/METHOD
 /// \endif
 class DnnPlane : public DynamicNearestNeighbours {
  public:
   /// empty initaliser
   DnnPlane() {}
 
   /// Initialiser from a set of points on an Eta-Phi plane, where both
   /// eta and phi can have arbitrary ranges
   DnnPlane(const std::vector<EtaPhi> &, const bool & verbose = false );
 
 
   /// Returns the index of  the nearest neighbour of point labelled
   /// by ii (assumes ii is valid)
   int NearestNeighbourIndex(const int ii) const ;
 
   /// Returns the distance to the nearest neighbour of point labelled
   /// by index ii (assumes ii is valid)
   double NearestNeighbourDistance(const int ii) const ;
 
   /// Returns true iff the given index corresponds to a point that
   /// exists in the DNN structure (meaning that it has been added, and
   /// not removed in the meantime)
   bool Valid(const int index) const;
 
   void RemoveAndAddPoints(const std::vector<int> & indices_to_remove,
               const std::vector<EtaPhi> & points_to_add,
               std::vector<int> & indices_added,
               std::vector<int> & indices_of_updated_neighbours);
 
   /// returns the EtaPhi of point with index i.
   EtaPhi etaphi(const int i) const;
   /// returns the eta point with index i.
   double eta(const int i) const;
   /// returns the phi point with index i.
   double phi(const int i) const;
 
 private:
 
   /// Structure containing a vertex_handle and cached information on
   /// the nearest neighbour.
   struct SuperVertex {
     Vertex_handle vertex; // NULL indicates inexistence...
     double NNdistance;
     int NNindex;
     int coincidence;  // ==vertex->info.val() if no coincidence
                       // points to the coinciding SV in case of coincidence
     // later on for cylinder put a second vertex?
   };
 
   std::vector<SuperVertex> _supervertex;
   //set<Vertex_handle> _vertex_set;
   bool _verbose;
 
   //static const bool _crash_on_coincidence = true;
   static const bool _crash_on_coincidence = false;
 
   Triangulation _TR; /// CGAL object for dealing with triangulations
 
   /// calculates and returns the euclidean distance between points p1
   /// and p2
   inline double _euclid_distance(const Point& p1, const Point& p2) const {
     double distx= p1.x()-p2.x();
     double disty= p1.y()-p2.y();
     return distx*distx+disty*disty;
   }
 
   //---------------------------------------------------------------------- 
   /// Determines the index and distance of the nearest neighbour to 
   /// point j and puts the information into the _supervertex entry for j
   void _SetNearest(const int j);
 
   //----------------------------------------------------------------------
   /// Determines and stores the nearest neighbour of j.
   ///
   /// For each voronoi neighbour D of j if the distance between j and D
   /// is less than D's own nearest neighbour, then update the
   /// nearest-neighbour info in D; push D's index onto 
   /// indices_of_updated_neighbours
   ///
   /// Note that j is NOT pushed onto indices_of_updated_neighbours --
   /// if you want it there, put it there yourself.
   void _SetAndUpdateNearest(const int j, 
                 std::vector<int> & indices_of_updated_neighbours);
 
   /// given a vertex_handle returned by CGAL on insertion of a new
   /// points, returns the coinciding vertex's value if it turns out
   /// that it corresponds to a vertex that we already knew about
   /// (usually because two points coincide)
   int _CheckIfVertexPresent(const Vertex_handle & vertex, 
                 const int its_index);
 
   //----------------------------------------------------------------------
   /// if the distance between 'pref' and 'candidate' is smaller (or
   /// equal) than the one between 'pref' and 'near', return true and
   /// set 'mindist' to that distance. Note that it is assumed that
   /// 'mindist' is the euclidian distance between 'pref' and 'near'
   ///
   /// Note that the 'near' point is passed through its vertex rather
   /// than as a point. This allows us to handle cases where we have no min
   /// yet (near is the infinite vertex)
   inline bool _is_closer_to(const Point &pref, 
                 const Point &candidate,
                 const Vertex_handle &near,
                 double & dist,
                 double & mindist){
     dist = _euclid_distance(pref, candidate);
     return _is_closer_to_with_hint(pref, candidate, near, dist, mindist);
   }
 
   /// same as '_is_closer_to' except that 'dist' already contains the
   /// distance between 'pref' and 'candidate'
   inline bool _is_closer_to_with_hint(const Point &pref, 
                       const Point &candidate,
                       const Vertex_handle &near,
                       const double & dist,
                       double & mindist){
     
     // check if 'dist', the pre-computed distance between 'candidate'
     // and 'pref' is smaller than the distance between 'pref' and its
     // currently registered nearest neighbour 'near' (and update
     // things if it is)
     //
     // Interestingly enough, it has to be pointed out that the use of
     // 'abs' instead of 'std::abs' returns wrong results (apparently
     // ints without any compiler warning)
     //
     // The (near != NULL) test is there for one single reason: when
     // checking that a newly inserted point is not closer than a
     // previous NN, if that distance comparison involves a "nearly
     // degenerate" distance we need to access near->point. But
     // sometimes, in the course of RemoveAndAddPoints, its previous NN
     // has been deleted and its vertex (corresponding to 'near') set
     // to NULL. This is not a problem as all points having a deleted
     // point as NN will have their NN explicitly recomputed at the end
     // of RemoveAndAddPoints so here we should just make sure there is
     // no crash... that's done by checking (near != NULL)
     if ((std::abs(dist-mindist)<DISTANCE_FOR_CGAL_CHECKS) &&
     _is_not_null(near) && // GPS cf. note below about != NULL with clang/CGAL
     (_euclid_distance(candidate, near->point())<DISTANCE_FOR_CGAL_CHECKS)){
       // we're in a situation where there might be a rounding issue,
       // use CGAL's distance computation to get it right
       //
       // Note that in the test right above,
       // (abs(dist-mindist)<1e-12) guarantees that the current
       // nearest point is not the infinite vertex and thus
       // nearest->point() is not ill-defined
       if (_verbose) std::cout << "using CGAL's distance ordering" << std::endl;
       if (CGAL::compare_distance_to_point(pref, candidate, near->point())!=CGAL::LARGER){
     mindist = dist;
     return true;
       }
     } else if (dist <= mindist) {
       // Note that the use of a <= in the above expression (instead of
       // a strict ordering <) is important in one case: when checking
       // if a new point is the new NN of one of the points in its
       // neighbourhood, in case of distances being ==, we are sure
       // that 'candidate' is in a cell adjacent to 'pref' while it may
       // no longer be the case for 'near'
       mindist = dist;
       return true;
     } 
     
     return false;
   }
 
   /// if a distance between a point and 2 others is smaller than this
   /// and the distance between the two points is also smaller than this
   /// then use CGAL to compare the distances. 
   static const double DISTANCE_FOR_CGAL_CHECKS;  
 
 
   /// small routine to check if if a vertex handle is not null.
   ///
   /// This is centralised here because of the need for a not-very
   /// readable workaround for certain CGAL/clang++ compiler
   /// combinations.
   inline static bool _is_not_null(const Vertex_handle & vh) {
     // as found in issue 2015-07-clang61+CGAL, the form
     //   vh != NULL
     // appears to be broken with CGAL-3.6 and clang-3.6.0/.1
     //
     // The not very "readable"
     //   vh.operator->()
     // does the job instead
     return vh.operator->();
   }
   
 };
 
 
 // here follow some inline implementations of the simpler of the
 // functions defined above
 
 inline int DnnPlane::NearestNeighbourIndex(const int ii) const {
   return _supervertex[ii].NNindex;}
 
 inline double DnnPlane::NearestNeighbourDistance(const int ii) const {
   return _supervertex[ii].NNdistance;}
 
 inline bool DnnPlane::Valid(const int index) const {
   if (index >= 0 && index < static_cast<int>(_supervertex.size())) {
     return _is_not_null(_supervertex[index].vertex);
   }
   else {
     return false;
   }
 }
 
 
 inline EtaPhi DnnPlane::etaphi(const int i) const {
   Point * p = & (_supervertex[i].vertex->point());
   return EtaPhi(p->x(),p->y()); }
 
 inline double DnnPlane::eta(const int i) const {
   return _supervertex[i].vertex->point().x(); }
 
 inline double DnnPlane::phi(const int i) const {
   return _supervertex[i].vertex->point().y(); }
 
 
 FASTJET_END_NAMESPACE
 
 #endif //  __FASTJET_DNNPLANE_HH__
 
 #endif // DROP_CGAL

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