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 // StringInteraction.h is a part of the PYTHIA event generator.
 // Copyright (C) 2024 Torbjorn Sjostrand.
 // PYTHIA is licenced under the GNU GPL v2 or later, see COPYING for details.
 // Please respect the MCnet Guidelines, see GUIDELINES for details.
 
 // Header file for the classes involved in the modelling interactions
 // between strings. This includes standard colour reconnections,
 // perturbative swing, string shoving and rope hadronisation. The
 // StringInterations base class is an interface to all of these, and
 // can be used both during and after PartonLevel, as well as before,
 // during and after string fragmentation.
 
 #ifndef Pythia8_StringInteractions_H
 #define Pythia8_StringInteractions_H
 
 #include "Pythia8/SharedPointers.h"
 #include "Pythia8/PhysicsBase.h"
 #include "Pythia8/FragmentationSystems.h"
 
 namespace Pythia8 {
 
 //==========================================================================
 
 // StringInteractions is the base class for handling colour
 // reconnection, swing, shoving, and rope-type models for modifying
 // string fragmentation.
 
 class StringInteractions : public PhysicsBase {
 
 public:
 
   // Empty constructor.
   StringInteractions() = default;
 
   // Empty virtual destructor
   virtual ~StringInteractions() {}
 
   // Function called from Pythia after the basic pointers.  The base
   // class will setup the standard behaviour of Pythia 8.2 according
   // to the given Settings. Derived classes should create objects of
   // the specific model objects to be used.
   virtual bool init();
 
   // Access the pointers to the different models.
   ColRecPtr getColourReconnections() const { return colrecPtr; }
   DipSwingPtr getDipoleSwing() const { return dipswingPtr; }
   StringRepPtr getStringRepulsion() const { return stringrepPtr; }
   FragModPtr getFragmentationModifier() const { return fragmodPtr; }
 
 protected:
 
   // The object responsible for colour reconections in the end of
   // PartonLevel or in the beginning of HadronLevel.
   ColRecPtr colrecPtr{};
 
   // The object responsible for the perturbative swing which is always
   // active together with the TimeShower.
   DipSwingPtr dipswingPtr{};
 
   // The object responsible for repulsion between strings before
   // hadronisation (or calculating the repulsion before but actually
   // pushing the hadrons after fragmentation).
   StringRepPtr stringrepPtr{};
 
   // The object responsible for modifying fragmentation parameters due
   // to string interactions in each break-up (eg. in rope
   // hadronisation).
   FragModPtr fragmodPtr{};
 
 };
 
 //==========================================================================
 
 // ColourReconnectionBase is responsible for doing standard colour
 // reconnection in the end of the PartonLevel or in the beginning of
 // HadronLevel.
 
 class ColourReconnectionBase : public PhysicsBase {
 
 public:
 
   // Empty default constructor.
   ColourReconnectionBase() = default;
 
   // Empty virtual destructor.
   virtual ~ColourReconnectionBase() {}
 
   // Called after PhysicsBase initHbPtrs has been called.
   virtual bool init() { return true; }
 
   // New beams possible for handling of hard diffraction.
   virtual void reassignBeamPtrs( BeamParticle* beamAPtrIn,
     BeamParticle* beamBPtrIn) {beamAPtr = beamAPtrIn;
     beamBPtr = beamBPtrIn;}
 
   // Do colour reconnection for current event.
   virtual bool next( Event & event, int oldSize) = 0;
 
 };
 
 //==========================================================================
 
 // DipoleSwingBase is responsible for the perturbative swing and is active
 // anytime the TimeShower is active.
 
 class DipoleSwingBase : public PhysicsBase {
 
 public:
 
   // Empty default constructor.
   DipoleSwingBase() = default;
 
   // Empty virtual destructor.
   virtual ~DipoleSwingBase() {}
 
   // Called after PhysicsBase initInfoPtr has been called.
   virtual bool init() { return true; }
 
   // New beams possible for handling of hard diffraction.
   virtual void reassignBeamPtrs( BeamParticle* beamAPtrIn,
     BeamParticle* beamBPtrIn, int beamOffsetIn = 0) {beamAPtr = beamAPtrIn;
     beamBPtr = beamBPtrIn; beamOffset = beamOffsetIn;}
 
   // Prepare system for evolution after each new interaction; identify ME.
   // Usage: prepare( iSys, event, limitPTmax).
   virtual void prepare( int , Event& , bool = true) = 0;
 
   // Update dipole list after a multiparton interactions rescattering.
   // Usage: rescatterUpdate( iSys, event).
   virtual void rescatterUpdate( int , Event& ) = 0;
 
   // Update dipole list after each ISR emission.
   // Usage: update( iSys, event, hasWeakRad).
   virtual void update( int , Event& , bool = false) = 0;
 
   // Select next pT in downwards evolution.
   // Usage: pTnext( event, pTbegAll, pTendAll, isFirstTrial, doTrialIn).
   virtual double pTnext( Event& , double , double ,
                          bool = false, bool = false) = 0;
 
   // Perform the swing previousl generated in pTnext.
   virtual bool swing( Event& event) = 0;
 
 protected:
 
   // Offset the location of the beam pointers in an event.
   int beamOffset{};
 
 };
 
 //==========================================================================
 
 // StringRepulsionBase is responsible for calculating and performing
 // the repulsion between strings before the hadronisation.
 
 class StringRepulsionBase : public PhysicsBase {
 
 public:
 
   // Empty default constructor.
   StringRepulsionBase() = default;
 
   // Empty virtual destructor.
   virtual ~StringRepulsionBase() {}
 
   // Called after PhysicsBase initInfoPtr has been called.
   virtual bool init() { return true; }
 
   // Main virtual function, called before the hadronisation.
   virtual bool stringRepulsion(Event & event, ColConfig & colConfig) = 0;
 
   // Additional functionality for implementing repulsion post-factum
   // after the actual hadronisation has been done.
   virtual bool hadronRepulsion(Event &) { return true; }
 };
 
 //==========================================================================
 
 // FragmentationModifierBase can change the parameters of the string
 // fragmentation in each break-up.
 
 class FragmentationModifierBase : public PhysicsBase {
 
 public:
 
   // Empty default constructor.
   FragmentationModifierBase() = default;
 
   // Empty virtual destructor.
   virtual ~FragmentationModifierBase() {};
 
   // Called after PhysicsBase initInfoPtr has been called.
   virtual bool init() { return true; }
 
   // Called just before hadronisation starts.
   virtual bool initEvent(Event& event, ColConfig& colConfig) = 0;
 
   // The main virtual function for chaning the fragmentation
   // parameters.
   virtual bool doChangeFragPar(StringFlav* flavPtr, StringZ* zPtr,
    StringPT * pTPtr, double m2Had, vector<int> iParton, int endId) = 0;
 
 };
 
 //==========================================================================
 
 } // end namespace Pythia8
 
 #endif // Pythia8_StringInteractions_H

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