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 // VinciaHistory.h is a part of the PYTHIA event generator.
 // Copyright (C) 2025 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.
 
 // Authors: Helen Brooks, Christian T Preuss
 // This file contains the VinciaHistory class.
 
 #ifndef VINCIA_History_H
 #define VINCIA_History_H
 
 #include "Pythia8/History.h"
 #include "Pythia8/Info.h"
 #include "Pythia8/Vincia.h"
 #include "Pythia8/VinciaAntennaFunctions.h"
 #include "Pythia8/VinciaMergingHooks.h"
 
 namespace Pythia8 {
 
 //==========================================================================
 
 // Convenient shorthand for storing ordered list of chains.
 
 struct PseudoChain {
   // Ordered list of concatenated chains.
   vector<int> chainlist;
   // Index unique up to chain content (not ordering).
   int index;
   // Charge Index.
   int cindex;
   // Does any of the chains contain an initial state parton.
   bool hasInitial;
   // Flavour at start of first and end of last.
   int flavStart;
   int flavEnd;
   // Charge.
   int charge;
 };
 
 //==========================================================================
 
 // A class for associating disconnected colour chains with either
 // resonances or the hard QCD scattering. Once fixed, the sector
 // history is deterministic.
 
 class ColourFlow {
 
  public:
 
   // Constructor.
   ColourFlow() : nChains(0), nBeamChainsMin(0), nBeamChainsMax(0), nRes(0) {
     for(int i=0; i<4; i++) {countChainsByChargeIndex[i]=0;
       countResByChargeIndex[i]=0;}}
 
   // Methods.
 
   // Add or assign chains.
   void addChain(int charge, int flavStart, int flavEnd, bool hasInitialIn);
   void selectResChains(int index,int iorder, int id);
   void selectBeamChains(int index,int iorder);
 
   // Initialise from hard process information.
   bool initHard(map<int, map<int,int> >& countRes,
     shared_ptr<VinciaMergingHooks> vinMergingHooksPtr);
 
   // Get information about current status of (pseudo)chains.
   bool checkChains(int cIndex);
   bool checkChains();
   int getNChainsLeft();
   int maxLength();
   int minLength();
 
   // Print information about (pseudo)chains.
   void print(bool printpsch = false);
 
   // Members.
 
   // Chains that arise from the decay of a resonance.
   map<int, vector<PseudoChain> > resChains;
 
   // Remaining list of ordered chains after resonances stripped off.
   vector<PseudoChain> beamChains;
 
   // Maps to all viable combinations of chains (of each charge)
   // from an index which depends on the identities of chains in it
   // - will be empty when resChains and beamChains set.
   map< int , vector< PseudoChain > > pseudochains;
 
   // Easy way to look up all pseudochains which contain a given chain.
   // Map from chain number to pseudochain index.
   map<int,vector<int> > chainToIndices;
 
   // Map from chain to the flavour at the start or end of that chain.
   map<int,int> chainStartToFlav;
   map<int,int> chainEndToFlav;
   // Keep track of chains which contain an initial state parton.
   map<int,bool> hasInitial;
   // Keep track of charge information of chains.
   map<int,int> chainToCharge;
 
  private:
 
   // Add or assign chains.
   void addChain(int oldIndex, int chainsIndex, int iChain,
     vector<int> & newIndices);
   void selectPseudochain(vector<int> & psch);
   void selectChain(int iChain);
 
   // Create empty vectors in resChains, and count each type.
   void addResonances(vector<int>& idsIn, map<int, map<int,int> >& idCounter,
     int charge, bool fc);
 
   // Convert charge information to an index.
   int getChargeIndex(int charge, bool fc);
 
   // Convert pseudochain to unique ID.
   int getID(PseudoChain& psc) {
     int id = 0;
     int iChains = psc.chainlist.size()-1;
     for (int iPwr(iChains); iPwr>=0; --iPwr)
       id += (psc.chainlist.at(iPwr)+1)*pow(10,iChains-iPwr);
     return id;
   }
 
   // List of found pseudochains to not double count.
   vector<int> pseudochainIDs;
 
   // Counters.
   int nChains;
   int nBeamChainsMin, nBeamChainsMax, nRes;
   map<int,int> countChainsByChargeIndex;
   map<int,int> countResByChargeIndex;
 
 };
 
 //==========================================================================
 
 // Class for a single step in the history of a process.
 
 class HistoryNode {
 
  public:
 
   // Constructors.
   HistoryNode() {};
   HistoryNode(Event& stateIn, vector< vector<int> > chainsIn,
     double scaleIn) : HistoryNode() {
     state = stateIn;
     clusterableChains = chainsIn;
     qEvolNow = scaleIn;
     hasRes = false;
     iRes = 0;
     idRes = 0;
     isInitPtr=false;
   };
 
   // Methods.
   void initPtr(VinciaCommon* vinComPtrIn, Resolution* resPtrIn,
     AntennaSetFSR* antSetPtrIn) {
     resPtr = resPtrIn;
     vinComPtr = vinComPtrIn;
     antSetFSRptr = antSetPtrIn;
     isInitPtr=true;
     nMinQQbar = 0;
   }
 
   // Set clusterList.
   int getNClusterings(shared_ptr<VinciaMergingHooks> vinMergingHooksPtr,
     Logger* loggerPtr, int verboseIn);
   void setClusterList(shared_ptr<VinciaMergingHooks> vinMergingHooksPtr,
     Logger* loggerPtr, int verboseIn);
 
   // Perform the clusterings according to the resolution criterion.
   bool cluster(HistoryNode& nodeClus,
     Logger* loggerPtr, int verboseIn);
 
   // Get energy fractions (used in PDF ratios).
   double xA() const {return 2. * state[3].e() / state[0].e();}
   double xB() const {return 2. * state[4].e() / state[0].e();}
 
   // Get flavours of beams (used in PDF ratios).
   int idA() const {return state[3].id();}
   int idB() const {return state[4].id();}
 
   // Get colour types of beams (used in PDF ratios).
   int colTypeA() const {return state[3].colType();}
   int colTypeB() const {return state[4].colType();}
 
   // Get evolution scale (used in trial shower).
   double getEvolNow() const {return qEvolNow;}
 
   // Setter methods.
   void setEvolScale(double scaleIn) {qEvolNow = scaleIn;}
 
   // Current state.
   Event state;
 
   // Resonance info.
   bool hasRes;
   int  iRes;
   int  idRes;
 
   // Minimal number of qqbar pairs.
   int nMinQQbar;
 
   // List of unclusterable lists of colour-connected partons.
   vector<vector<int>> clusterableChains;
 
   // Information corresponding to the last clustering.
   VinciaClustering lastClustering;
 
  private:
 
   // Perform a clustering.
   bool doClustering(VinciaClustering& clus, Event& clusEvent,
     vector<vector<int>>& clusChains, Logger* loggerPtr, int verboseIn);
 
   // Methods to calculate resolution and evolution scales.
   double calcResolution(VinciaClustering& clusIn) {
     return resPtr->q2sector(clusIn);}
   double calcEvolScale(VinciaClustering& clusIn) {
     return resPtr->q2evol(clusIn);}
 
   // Members.
 
   // Vincia pointers.
   Resolution*    resPtr;
   VinciaCommon*  vinComPtr;
   AntennaSetFSR* antSetFSRptr;
 
   bool isInitPtr;
 
   // The value of the evolution scale.
   double qEvolNow;
 
   // List of next possible clusterings.
   // Map is from corresponding resolution criterion.
   map<double, VinciaClustering> clusterList;
 
 };
 typedef map<int, vector<HistoryNode> > HistoryNodes;
 
 //==========================================================================
 
 // History class for the Vincia shower.
 
 class VinciaHistory {
 
 public:
 
   // Constructor.
   VinciaHistory(Event &stateIn,
     BeamParticle* beamAPtrIn, BeamParticle* beamBPtrIn,
     MergingHooksPtr mergingHooksPtrIn,
     PartonLevel* trialPartonLevelPtrIn,
     ParticleData* particleDataPtrIn,
     Info* infoPtrIn);
 
   // Check if a valid history was found.
   bool isValid() {return foundValidHistory;}
 
   // Check if history failed merging scale cut.
   bool isBelowMS() {return failedMSCut;}
 
   // Perform a trial shower and get the CKKW-L weight
   // (excluding last no-emission probability that is
   // calculated in the main shower).
   double getWeightCKKWL();
 
   // Find the first clustered state above the merging scale.
   Event getFirstClusteredEventAboveTMS();
 
   // What was the multiplicity of this event?
   int getNClusterSteps();
 
   // Get the shower starting scale.
   double getRestartScale();
 
   // Should we overwrite the original event?
   // E.g. if an MPI was generated.
   bool  hasNewProcess() {return hasNewProcessSav;}
   Event getNewProcess() {return newProcess;}
   bool  doAbort() {return aborted;}
 
 private:
 
   // Loop over colPerms and set historyBest.
   void findBestHistory();
 
   // Find all viable colour orderings and return number.
   unsigned int countPerms();
 
   // Fetch the colour chains from the hard event.
   bool getColChains();
 
   // Find all selections of chains for colour singlets.
   bool assignResChains(map<int, map<int,int>>& idCounter,
     vector<ColourFlow>& flowsSoFar);
 
   // Find all selections of chains for colour singlets.
   bool assignResFromEvent(map<int, map<int,int>>& idCounter,
     vector<ColourFlow>& flowsSoFar);
 
   // Find all selections of chains for everything that is
   // not a colour singlet resonance.
   bool assignBeamChains(vector<ColourFlow>& flowsSoFar);
 
   // Make a single selection in all possible ways.
   bool assignNext(vector<ColourFlow>& flowsSoFar, bool isRes = false,
     int id = 0, int cIndex = 0);
 
   // Make a specific selection for a resonance.
   bool assignThis(vector<ColourFlow>& flowsSoFar, int id, int cIndex,
     vector<int>& chains);
 
   // Is this (completed flow) compatible with the number of
   // resonances of each type?
   bool check(ColourFlow& flow);
 
   // Construct history for a given colour permutation.
   tuple<bool, double, HistoryNodes> findHistoryPerm(ColourFlow& flow);
 
   // Check if history failed merging scale cut.
   bool checkMergingCut(HistoryNodes& history);
 
   // Initialise history nodes for each system.
   HistoryNodes initHistoryNodes(ColourFlow& flow );
 
   // Translate abstract book-keeping of colour ordering into
   // systems of particles.
   map<int, vector<vector<int>>> getSystems(ColourFlow& flow,
     map<int, int>& sysToRes);
 
   // Decide if state is the Born topology.
   bool isBorn(const HistoryNode& nodeIn, bool isRes);
 
   // Set up beams for given history node.
   bool setupBeams(const HistoryNode* node, double scale2);
 
   // Calculate criterion for testing whether to keep history.
   double calcME2guess(vector<HistoryNode>& history,bool isRes);
   // Calculate ME for Born-level event.
   double calcME2Born(const HistoryNode& bornNode, bool isRes);
 
   // Calculate the antenna function for a given clustering.
   double calcAntFun(const VinciaClustering& clusNow);
 
   // Calculate PDF ratio to multiply CKKW-L weight.
   double calcPDFRatio(const HistoryNode* nodeNow,
     double pT2now, double pT2next);
 
   // Calculate alphaS ratio to multiply CKKW-L weight.
   double calcAlphaSRatio(const HistoryNode& node);
 
   // Return the kinematic maximum for this event.
   double getStartScale(Event& event, bool isRes);
 
   // Perform a trial branching and return scale.
   double qNextTrial(double qStart, Event& evtIn);
 
   // Print colour chains.
   void printChains();
 
   // Verbosity.
   int verbose;
 
   // Beams -- for PDFs.
   BeamParticle beamA, beamB;
 
   // MergingHooks.
   shared_ptr<VinciaMergingHooks> vinMergingHooksPtr{};
 
   // PartonLevel pointer.
   PartonLevel* trialPartonLevel{};
 
   // Particle data pointer.
   ParticleData* particleDataPtr{};
 
   // Other Pythia pointers.
   Info* infoPtr{};
   Logger* loggerPtr{};
 
   // Vincia pointers.
   shared_ptr<VinciaFSR> fsrShowerPtr{};
   shared_ptr<VinciaISR> isrShowerPtr{};
   MECs*                 mecsPtr{};
   VinciaCommon*         vinComPtr{};
   Resolution*           resPtr{};
   AntennaSetFSR*        antSetFSRptr{};
 
   // Check we found a valid history at all.
   bool foundValidHistory;
 
   // Check we vetoed due failing the merging scale cut.
   bool failedMSCut;
 
   // This is the best PS history so far.
   HistoryNodes historyBest;
 
   // Criterion to minimise (best so far).
   // Call calcME2guess(..) to evaluate.
   double ME2guessBest;
 
   // Initial colour permutation, stored as
   // list of sets of colour connected partons.
   vector<vector<int>> colChainsSav;
 
   // Track if chain contains initial state quarks.
   map<int, bool> chainHasInitial;
 
   // Keep track of resonances in the event record.
   map<int, vector<int>> resIDToIndices;
   map<int, vector<int>> resIndexToChains;
 
   // All colour flows compatible with Born process.
   vector<ColourFlow> colPerms;
 
   // ME generated event.
   Event state;
 
   // Number of quarks  and gluon loops in event.
   int nQSave, nGluonLoopsSave;
 
   // The merging scale and whether it is the evolution variable.
   double qms;
   bool   msIsEvolVar;
 
   // The maximum multiplicity of our ME generator.
   int nMax, nMaxRes;
 
   // Possible new hard process info (if MPI was generated).
   bool   hasNewProcessSav;
   Event  newProcess;
   double newProcessScale;
 
   // Flag to signal if something went wrong.
   bool aborted;
 
 };
 
 //==========================================================================
 
 } // end namespace Pythia8
 
 #endif // Pythia8_VinciaHistory_H

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