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 // $Id: RecursiveLundEEGenerator.hh 1465 2024-12-11 14:53:28Z gsoyez $
 //
 // Copyright (c) 2018-, Frederic A. Dreyer, Keith Hamilton, Alexander Karlberg,
 // Gavin P. Salam, Ludovic Scyboz, Gregory Soyez, Rob Verheyen
 //
 //----------------------------------------------------------------------
 // This file is part of FastJet contrib.
 //
 // It 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.
 //
 // It 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 this code. If not, see <http://www.gnu.org/licenses/>.
 //----------------------------------------------------------------------
 
 #ifndef __FASTJET_CONTRIB_RECURSIVELUNDEEGENERATOR_HH__
 #define __FASTJET_CONTRIB_RECURSIVELUNDEEGENERATOR_HH__
 
 #include "fastjet/contrib/LundEEHelpers.hh"
 
 #include <fastjet/internal/base.hh>
 #include "fastjet/tools/Recluster.hh"
 #include "fastjet/JetDefinition.hh"
 #include "fastjet/PseudoJet.hh"
 #include <string>
 #include <vector>
 #include <utility>
 #include <queue>
 
 using namespace std;
 
 FASTJET_BEGIN_NAMESPACE
 
 namespace contrib{
 
 //----------------------------------------------------------------------
 /// \class LundEEDeclustering
 /// Contains the declustering variables associated with a single node
 /// on the LundEE plane
 class LundEEDeclustering {
 public:
 
   /// return the pair PseudoJet, i.e. sum of the two subjets
   const PseudoJet & pair()  const {return pair_;}
   /// returns the subjet with larger transverse momentum
   const PseudoJet & harder() const {return harder_;}
   /// returns the subjet with smaller transverse momentum
   const PseudoJet & softer() const {return softer_;}
 
 
   /// returns pair().m() [cached]
   double m()         const {return m_;}
 
   /// returns the effective pseudorapidity of the emission [cached]
   double eta()       const {return eta_;}
 
   /// returns sin(theta) of the branching [cached]
   double sin_theta() const {return sin_theta_;}
 
   /// returns softer().modp() / (softer().modp() + harder().modp()) [cached]
   double z()         const {return z_;}
 
   /// returns softer().modp() * sin(theta()) [cached]
   double kt()        const {return kt_;}
 
   /// returns ln(softer().modp() * sin(theta())) [cached]
   double lnkt()      const {return lnkt_;}
 
   /// returns z() * Delta() [cached]
   double kappa()     const {return kappa_;}
 
   /// returns the index of the plane to which this branching belongs
   int iplane() const {return iplane_;}
 
   /// returns the depth of the plane on which this declustering
   /// occurred. 0 is the primary plane, 1 is the first set of leaves, etc. 
   int depth() const {return depth_;}
   
   /// returns iplane (plane index) of the leaf associated with the
   /// potential further declustering of the softer of the objects in
   /// this splitting
   int leaf_iplane() const {return leaf_iplane_;}
 
   /// Returns sign_s, indicating the initial parent jet index of this splitting
   int sign_s() const {return sign_s_;}
   
   /// returns an azimuthal angle psibar associated with this
   /// declustering. The actual value of psibar is arbitrary and IR
   /// unsafe (but see below), while differences in psibar values between
   /// different clusterings are meaningful.
   ///
   /// The absolute value of psibar should in general not be used,  but
   /// it has the following properties. (1) the first (largest-angle) splitting
   /// ("ref") in the positive-z hemisphere defines psibar=0 (if there is
   /// no splitting in that hemisphere then the first splitting in
   /// the negative-z hemisphere does). If the +z jet aligns along the z
   /// axis, then psibar of collinear splitting i in that jet is 
   ///
   ///   psibar_i = phi_i - phi_ref
   ///
   /// For the negative-z jet, the psibar of collinear splitting i is
   ///
   ///   psibar_i = phi_i - pi - phi_ref
   ///
   double psibar()    const {return psibar_;}
 
   /// (DEPRECATED)
   /// returns an azimuthal type angle between this declustering plane and the previous one
   /// Note: one should use psibar() instead, since we found that this definition of psi is
   /// not invariant under rotations of the event
   double psi()       const {return psi_;}
 
   /// update the azimuthal angle (deprecated)
   void set_psi(double psi) {psi_ = psi;}
 
 
   /// returns the coordinates in the Lund plane
   std::pair<double,double> const lund_coordinates() const {
     return std::pair<double,double>(eta_,lnkt_);
   }
 
   virtual ~LundEEDeclustering() {}
 
 private:
   int iplane_;
   double psi_, psibar_, lnkt_, eta_;
   double m_, z_, kt_, kappa_, sin_theta_;
   PseudoJet pair_, harder_, softer_;
   int  depth_ = -1, leaf_iplane_ = -1;
   int sign_s_;
 
 protected:
 
   /// default ctor (protected, should not normally be needed by users,
   /// but can be useful for derived classes)
   LundEEDeclustering() {}
 
   /// the constructor is protected, because users will not generally be
   /// constructing a LundEEDeclustering element themselves.
   LundEEDeclustering(const PseudoJet& pair,
              const PseudoJet& j1, const PseudoJet& j2,
              int iplane = -1, double psi = 0.0, double psibar = 0.0, int depth = -1, int leaf_iplane = -1, int sign_s = 1);
 
   friend class RecursiveLundEEGenerator;
 
 };
 
 
 /// Default comparison operator for LundEEDeclustering, using kt as the ordering.
 /// Useful when including declusterings in structures like priority queues
 inline bool operator<(const LundEEDeclustering& d1, const LundEEDeclustering& d2) {
   return d1.kt() < d2.kt();
 }
 
 //----------------------------------------------------------------------  
 /// Class to carry out Lund declustering to get anything from the
 /// primary Lund plane declusterings to the full Lund diagram with all
 /// its leaves, etc.
 class RecursiveLundEEGenerator {
  public:
   /// constructs a RecursiveLundEEGenerator with the specified depth.
   /// - depth = 0 means only primary declusterings are registered
   /// - depth = 1 means the first set of leaves are declustered
   /// - ...
   /// - depth < 0 means no limit, i.e. recurse through all leaves
   ///
   /// The psibar values that are set in the result Lund tree have the
   /// following property:
   ///
   /// - if the jet with the larger pz has splittings, then its
   ///   first splitting has psibar = 0
   /// - otherwise the first splitting of the other jet has psibar = 0
   ///
   /// Note that this makes psibar IR unsafe (because an arbitrarily soft
   /// splitting can be the one that gets the reference psibar=0 value), 
   /// but differences between psibar values are IR safe.
   /// 
   /// NB: The dynamical_psi_ref option relates to the deprecated definition of psi
   /// New code should use the psibar() function and dynamical_psi_ref
   /// is irrelevant.
   RecursiveLundEEGenerator(int max_depth = 0, bool dynamical_psi_ref = false) :
     max_depth_(max_depth), nx_(1,0,0,0), ny_(0,1,0,0), dynamical_psi_ref_(dynamical_psi_ref)
   {}
 
   /// destructor
   virtual ~RecursiveLundEEGenerator() {}
 
   /// This takes a cluster sequence with an e+e- C/A style algorithm, e.g.
   /// EECambridgePlugin(ycut=1.0).
   ///
   /// The output is a vector of LundEEDeclustering objects, ordered
   /// according to kt
   virtual std::vector<LundEEDeclustering> result(const ClusterSequence & cs) const {
     std::vector<PseudoJet> exclusive_jets = cs.exclusive_jets(2);
     assert(exclusive_jets.size() == 2);
     
     // order the two jets according to momentum along z axis
     if (exclusive_jets[0].pz() < exclusive_jets[1].pz()) {
       std::swap(exclusive_jets[0],exclusive_jets[1]);
     }
 
     PseudoJet d_ev = exclusive_jets[0] - exclusive_jets[1];
     lund_plane::Matrix3 rotmat = lund_plane::Matrix3::from_direction(d_ev);
     
     std::vector<LundEEDeclustering> declusterings;
     int depth = 0;
     int max_iplane_sofar = 1;
 
 // 2024-01: new code, that fixes up issue of psibar differences
 // between hemispheres. If RLEEG_NEWPSIBAR is false, answers
 // will come out wrong.
 #define RLEEG_NEWPSIBAR
 #ifdef RLEEG_NEWPSIBAR
     // 2024-01 -- attempt at new definition of psibar
     PseudoJet ref_plane;
     double last_psibar = 0.;
     bool first_time = true;
 
     for (unsigned ijet = 0; ijet < exclusive_jets.size(); ijet++) {
       int sign_s = ijet == 0? +1 : -1;
       append_to_vector(declusterings, exclusive_jets[ijet], depth, ijet, max_iplane_sofar,
                         rotmat, sign_s, ref_plane, last_psibar, first_time);
     }
 #else 
     for (unsigned ijet = 0; ijet < exclusive_jets.size(); ijet++) {
 
       // reference direction for psibar calculation
       PseudoJet axis = d_ev/sqrt(d_ev.modp2());
       PseudoJet ref_plane = axis;
 
       int sign_s = ijet == 0? +1 : -1;
       bool
       // We can pass a vector normal to a plane of reference for phi definitions
       append_to_vector(declusterings, exclusive_jets[ijet], depth, ijet, max_iplane_sofar,
                        rotmat, sign_s, ref_plane, 0., true);
     }
 #endif
 
     // a typedef to save typing below
     typedef LundEEDeclustering LD;
     // sort so that declusterings are returned in order of decreasing
     // kt (if result of the lambda is true, then first object appears
     // before the second one in the final sorted list)
     sort(declusterings.begin(), declusterings.end(),
          [](const LD & d1, const LD & d2){return d1.kt() > d2.kt();});
 
     return declusterings;
   }
   
  private:
 
   /// internal routine to recursively carry out the declusterings,
   /// adding each one to the declusterings vector; the primary
   /// ones are dealt with first (from large to small angle),
   /// and then secondary ones take place.
   void append_to_vector(std::vector<LundEEDeclustering> & declusterings,
                         const PseudoJet & jet, int depth,
                         int iplane, int & max_iplane_sofar,
                         const lund_plane::Matrix3 & rotmat, int sign_s,
                         PseudoJet & psibar_ref_plane,
                         const double & last_psibar, bool & first_time) const {
     PseudoJet j1, j2;
     if (!jet.has_parents(j1, j2)) return;
     if (j1.modp2() < j2.modp2()) std::swap(j1,j2);
 
     // calculation of azimuth psi
     lund_plane::Matrix3 new_rotmat;
     if (dynamical_psi_ref_) {
       new_rotmat = lund_plane::Matrix3::from_direction(rotmat.transpose()*(sign_s*jet)) * rotmat;
     } else {
       new_rotmat = rotmat;
     }
     PseudoJet rx = new_rotmat * nx_;
     PseudoJet ry = new_rotmat * ny_;
     PseudoJet u1 = j1/j1.modp(), u2 = j2/j2.modp();
     PseudoJet du = u2 - u1;
     double x = du.px() * rx.px() + du.py() * rx.py() + du.pz() * rx.pz();
     double y = du.px() * ry.px() + du.py() * ry.py() + du.pz() * ry.pz();
     double psi = atan2(y,x);
 
     // calculation of psibar
     double psibar = 0.;
     PseudoJet n1, n2;
 
     // First psibar for this jet
     if (first_time) {
 
 #ifdef RLEEG_NEWPSIBAR
 // 2024-01: new code, that fixes up issue of psibar differences
 // between hemispheres
       assert(last_psibar == 0.0);
       psibar = 0.0;
       n2 = lund_plane::cross_product(j1,j2);
       n2 /= n2.modp();
       psibar_ref_plane = n2;
       first_time = false;
 #else 
       // Compute the angle between the planes spanned by (some axis,j1) and by (j1,j2)
       n1 = lund_plane::cross_product(psibar_ref_plane,j1);
       n2 = lund_plane::cross_product(j1,j2);
 
       double signed_angle = 0.;
       n2 /= n2.modp();
       if (n1.modp() != 0) {
         n1 /= n1.modp();
         signed_angle = lund_plane::signed_angle_between_planes(n1,n2,j1);
       }
 
       psibar = lund_plane::map_to_pi(j1.phi() + signed_angle);
 #endif
     }
     // Else take the value of psibar_i and the plane from the last splitting to define psibar_{i+1}
     // The signed angle is multiplied by sign_s (+1 for the +z hemisphere, -1 for the -z hemisphere)
     // to take the correct orientation into account.
     else {
       n2 = lund_plane::cross_product(j1,j2);
       n2 /= n2.modp();
       psibar = lund_plane::map_to_pi(last_psibar + sign_s*lund_plane::signed_angle_between_planes(psibar_ref_plane, n2, j1));
     }
 
     int leaf_iplane = -1;
     // we will recurse into the softer "parent" only if the depth is
     // not yet at its limit or if there is no limit on the depth (max_depth<0)
     bool recurse_into_softer = (depth < max_depth_ || max_depth_ < 0);
     if (recurse_into_softer) {
       max_iplane_sofar += 1;
       leaf_iplane = max_iplane_sofar;
     }
     
     LundEEDeclustering declust(jet, j1, j2, iplane, psi, psibar, depth, leaf_iplane, sign_s);
     declusterings.push_back(declust);
 
     // now recurse
     // for the definition of psibar, we recursively pass the last splitting plane (normal to n2) and the last value
     // of psibar
     bool lcl_first_time = false;
     append_to_vector(declusterings, j1, depth, iplane, max_iplane_sofar, new_rotmat, sign_s, n2, psibar, lcl_first_time);
     if (recurse_into_softer) {
       append_to_vector(declusterings, j2, depth+1, leaf_iplane, max_iplane_sofar, new_rotmat, sign_s, n2, psibar, lcl_first_time);
     }
   }
   
   int max_depth_ = 0;
   /// vectors used to help define psi
   PseudoJet nx_;
   PseudoJet ny_;
   bool dynamical_psi_ref_;
 };
   
 } // namespace contrib
 
 FASTJET_END_NAMESPACE
 
 /// for output of declustering information
 std::ostream & operator<<(std::ostream & ostr, const fastjet::contrib::LundEEDeclustering & d);
 
 #endif  // __FASTJET_CONTRIB_RECURSIVELUNDEEGENERATOR_HH__

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