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 // Copyright (c) 2005-2021, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
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 // This file is part of FastJet.
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 //  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
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 //  The algorithms that underlie FastJet have required considerable
 //  development. They are described in the original FastJet paper,
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 #ifndef DROP_CGAL // in case we do not have the code for CGAL
 #ifndef __FASTJET_DNN3PICYLINDER_HH__
 #define __FASTJET_DNN3PICYLINDER_HH__
 
 #include "fastjet/internal/DynamicNearestNeighbours.hh"
 #include "fastjet/internal/DnnPlane.hh"
 #include "fastjet/internal/numconsts.hh"
 
 FASTJET_BEGIN_NAMESPACE      // defined in fastjet/internal/base.hh
 
 /// \if internal_doc
 /// @ingroup internal
 /// \class Dnn3piCylinder
 /// class derived from DynamicNearestNeighbours that provides an
 /// implementation for the surface of cylinder (using one 
 /// DnnPlane object spanning 0--3pi).
 /// \endif
 class Dnn3piCylinder : public DynamicNearestNeighbours {
  public:
   /// empty initaliser
   Dnn3piCylinder() {}
 
   /// Initialiser from a set of points on an Eta-Phi plane, where
   /// eta can have an arbitrary ranges and phi must be in range
   /// 0 <= phi < 2pi;
   /// 
   /// NB: this class is more efficient than the plain Dnn4piCylinder
   /// class, but can give wrong answers when the nearest neighbour is
   /// further away than 2pi (in this case a point's nearest neighbour
   /// becomes itself, because it is considered to be a distance 2pi
   /// away). For the kt-algorithm (e.g.) this is actually not a
   /// problem (the distance need only be accurate when it is less than
   /// R), so we can tell the routine to ignore this problem --
   /// alternatively the routine will crash if it detects it occurring
   /// (only when finding the nearest neighbour index, not its
   /// distance).
   Dnn3piCylinder(const std::vector<EtaPhi> &,
          const bool & ignore_nearest_is_mirror = false,
          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);
 
   ~Dnn3piCylinder();
 
  private:
 
   // our extras to help us navigate, find distance, etc.
   const static int INEXISTENT_VERTEX=-3;
 
   bool _verbose;
 
   bool _ignore_nearest_is_mirror;
 
   /// Picture of how things will work... Copy 0--pi part of the 0--2pi
   /// cylinder into a region 2pi--3pi of a Euclidean plane. Below we
   /// show points labelled by + that have a mirror image in this
   /// manner, while points labelled by * do not have a mirror image.
   ///                     
   ///      |           .     |        
   ///      |           .     |        
   ///      |           .     |        
   ///      |           .     |        
   ///      |        2  .     |        
   ///      |        *  .     |        
   ///      | +         . +   |        
   ///      | 0         . 1   |
   ///      |           .     |
   ///      0          2pi   3pi
   ///            
   /// Each "true" point has its true "cylinder" index (the index that
   /// is known externally to this class) as well as euclidean plane
   /// indices (main_index and mirror index in the MirrorVertexInfo
   /// structure), which are private concepts of this class.
   /// 
   /// In above picture our structures would hold the following info
   /// (the picture shows the euclidean-plane numbering)
   ///
   /// _mirror_info[cylinder_index = 0] = (0, 1)
   /// _mirror_info[cylinder_index = 1] = (2, INEXISTENT_VERTEX)
   ///
   /// We also need to be able to go from the euclidean plane indices
   /// back to the "true" cylinder index, and for this purpose we use
   /// the vector _cylinder_index_of_plane_vertex[...], which in the above example has
   /// the following contents
   ///
   /// _cylinder_index_of_plane_vertex[0] = 0
   /// _cylinder_index_of_plane_vertex[1] = 0
   /// _cylinder_index_of_plane_vertex[2] = 1
   ///
 
   /// 
   struct MirrorVertexInfo {
     /// index of the given point (appearing in the range 0--2pi) in the 
     /// 0--3pi euclidean plane structure (position will coincide with
     /// that on the 0--2pi cylinder, but index labelling it will be
     /// different)
     int main_index; 
     /// index of the mirror point (appearing in the range 2pi--3pi) in the
     /// 0--3pi euclidean plane structure
     int mirror_index; 
   };
 
   // for each "true" vertex we have reference to indices in the euclidean
   // plane structure
   std::vector<MirrorVertexInfo> _mirror_info;
   // for each index in the euclidean 0--3pi plane structure we want to
   // be able to get back to the "true" vertex index on the overall
   // 0--2pi cylinder structure
   std::vector<int> _cylinder_index_of_plane_vertex;
 
   // NB: we define POINTERS here because the initialisation gave
   //     us problems (things crashed!), perhaps because in practice
   //     we were making a copy without being careful and defining
   //     a proper copy constructor.
   DnnPlane * _DNN;
 
   /// given a phi value in the 0--2pi range return one 
   /// in the pi--3pi range.
   inline EtaPhi _remap_phi(const EtaPhi & point) {
     double phi = point.second;
     if (phi < pi) { phi += twopi ;}
     return EtaPhi(point.first, phi);}
 
 
   //----------------------------------------------------------------------
   /// What on earth does this do?
   ///
   /// Example: last true "cylinder" index was 15
   ///          last plane index was 23
   /// 
   /// Then: _cylinder_index_of_plane_vertex.size() = 24 and 
   ///       _mirror_info.size() = 16
   ///
   /// IF cylinder_point's phi < pi then
   ///   create:  _mirror_info[16] = (main_index = 24, mirror_index=25) 
   ///            _cylinder_index_of_plane_vertex[24] = 16
   ///            _cylinder_index_of_plane_vertex[25] = 16
   /// ELSE
   ///  create: _mirror_info[16] = (main_index = 24, mirror_index=INEXISTENT..) 
   ///          _cylinder_index_of_plane_vertex[24] = 16
   ///
   /// ADDITIONALLY push the cylinder_point (and if it exists the mirror
   /// copy) onto the vector plane_points.
   void _RegisterCylinderPoint (const EtaPhi & cylinder_point,
                    std::vector<EtaPhi> & plane_points);
 };
 
 
 // here follow some inline implementations of the simpler of the
 // functions defined above
 
 //----------------------------------------------------------------------
 /// Note: one of the difficulties of the 0--3pi mapping is that
 /// a point may have its mirror copy as its own nearest neighbour
 /// (if no other point is within a distance of 2pi). This does
 /// not matter for the kt_algorithm with
 /// reasonable values of radius, but might matter for a general use
 /// of this algorithm -- depending on whether or not the user has
 /// initialised the class with instructions to ignore this problem the
 /// program will detect and ignore it, or crash.
 inline int Dnn3piCylinder::NearestNeighbourIndex(const int current) const {
   int main_index = _mirror_info[current].main_index;
   int mirror_index = _mirror_info[current].mirror_index;
   int plane_index;
   if (mirror_index == INEXISTENT_VERTEX ) {
     plane_index = _DNN->NearestNeighbourIndex(main_index);
   } else {
     plane_index = (
     _DNN->NearestNeighbourDistance(main_index) < 
     _DNN->NearestNeighbourDistance(mirror_index)) ? 
       _DNN->NearestNeighbourIndex(main_index) : 
       _DNN->NearestNeighbourIndex(mirror_index) ; 
   }
   int this_cylinder_index = _cylinder_index_of_plane_vertex[plane_index];
   // either the user has acknowledged the fact that they may get the
   // mirror copy as the closest point, or crash if it should occur
   // that mirror copy is the closest point.
   assert(_ignore_nearest_is_mirror || this_cylinder_index != current);
   //if (this_cylinder_index == current) {
   //  std::cerr << "WARNING point "<<current<<
   //    " has its mirror copy as its own nearest neighbour"<<endl;
   //}
   return this_cylinder_index;
 }
 
 inline double Dnn3piCylinder::NearestNeighbourDistance(const int current) const {
   int main_index = _mirror_info[current].main_index;
   int mirror_index = _mirror_info[current].mirror_index;
   if (mirror_index == INEXISTENT_VERTEX ) {
     return _DNN->NearestNeighbourDistance(main_index);
   } else {
     return (
     _DNN->NearestNeighbourDistance(main_index) < 
     _DNN->NearestNeighbourDistance(mirror_index)) ? 
       _DNN->NearestNeighbourDistance(main_index) : 
       _DNN->NearestNeighbourDistance(mirror_index) ; 
   }
  
 }
 
 inline bool Dnn3piCylinder::Valid(const int index) const {
   return (_DNN->Valid(_mirror_info[index].main_index));
 }
 
 
 inline Dnn3piCylinder::~Dnn3piCylinder() {
   delete _DNN; 
 }
 
 
 FASTJET_END_NAMESPACE
 
 #endif //  __FASTJET_DNN3PICYLINDER_HH__
 #endif //  DROP_CGAL 

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