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 // MergingHooks.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.
 
 // This file is written by Stefan Prestel.
 // Header file to allow user access to program at different stages.
 // HardProcess: Container class for the hard process to be merged. Holds the
 //              bookkeeping of particles not be be reclustered
 // MergingHooks: Steering class for matrix element merging. Some functions can
 //               be redefined in a derived class to have access to the merging
 
 #ifndef Pythia8_MergingHooks_H
 #define Pythia8_MergingHooks_H
 
 #include "Pythia8/Basics.h"
 #include "Pythia8/BeamParticle.h"
 #include "Pythia8/Event.h"
 #include "Pythia8/Info.h"
 #include "Pythia8/ParticleData.h"
 #include "Pythia8/PartonSystems.h"
 #include "Pythia8/PhysicsBase.h"
 #include "Pythia8/PythiaStdlib.h"
 #include "Pythia8/Settings.h"
 
 
 namespace Pythia8 {
 
 class PartonLevel;
 
 //==========================================================================
 
 // Declaration of hard process class
 // This class holds information on the desired hard 2->2 process
 // for the merging.
 // This class is a container class for History class use.
 
 class HardProcess {
 
 public:
 
    // Flavour of the first incoming particle
   int hardIncoming1;
   // Flavour of the second incoming particle
   int hardIncoming2;
   // Flavours of the outgoing particles
   vector<int> hardOutgoing1;
   vector<int> hardOutgoing2;
   // Flavour of intermediate bosons in the hard 2->2
   vector<int> hardIntermediate;
 
   // Current reference event
   Event state;
   // Potential positions of outgoing particles in reference event
   vector<int> PosOutgoing1;
   vector<int> PosOutgoing2;
   // Potential positions of intermediate bosons in reference event
   vector<int> PosIntermediate;
 
   // Information on merging scale read from LHE file
   double tms;
 
   // Default constructor
   HardProcess() : hardIncoming1(), hardIncoming2(), tms(){}
   // Default destructor
   virtual ~HardProcess(){}
 
   // Copy constructor
   HardProcess( const HardProcess& hardProcessIn )
     : state(hardProcessIn.state),
       tms(hardProcessIn.tms) {
     hardIncoming1 = hardProcessIn.hardIncoming1;
     hardIncoming2 = hardProcessIn.hardIncoming2;
     for(int i =0; i < int(hardProcessIn.hardOutgoing1.size());++i)
       hardOutgoing1.push_back( hardProcessIn.hardOutgoing1[i]);
     for(int i =0; i < int(hardProcessIn.hardOutgoing2.size());++i)
       hardOutgoing2.push_back( hardProcessIn.hardOutgoing2[i]);
     for(int i =0; i < int(hardProcessIn.hardIntermediate.size());++i)
       hardIntermediate.push_back( hardProcessIn.hardIntermediate[i]);
     for(int i =0; i < int(hardProcessIn.PosOutgoing1.size());++i)
       PosOutgoing1.push_back( hardProcessIn.PosOutgoing1[i]);
     for(int i =0; i < int(hardProcessIn.PosOutgoing2.size());++i)
       PosOutgoing2.push_back( hardProcessIn.PosOutgoing2[i]);
     for(int i =0; i < int(hardProcessIn.PosIntermediate.size());++i)
       PosIntermediate.push_back( hardProcessIn.PosIntermediate[i]);
   }
 
   // Constructor with path to LHE file
   HardProcess( string LHEfile, ParticleData* particleData) : hardIncoming1(),
     hardIncoming2(), tms() {
     state = Event();
     state.init("(hard process)", particleData);
     translateLHEFString(LHEfile);
   }
 
   // Constructor with core process input
   virtual void initOnProcess( string process, ParticleData* particleData);
 
   // Constructor with path to LHE file input
   void initOnLHEF( string LHEfile, ParticleData* particleData);
 
   // Function to access the LHE file and read relevant information
   void translateLHEFString( string LHEpath);
 
   // Function to translate the process string (in MG/ME notation)
   virtual void translateProcessString( string process);
 
   // Function to clear hard process information
   void clear();
 
   // Function to check whether the sets of candidates Pos1, Pos2, together
   // with the proposed candidate iPos give an allowed hard process state
   virtual bool allowCandidates(int iPos, vector<int> Pos1, vector<int> Pos2,
     const Event& event);
   // Function to identify the hard subprocess in the current event
   virtual void storeCandidates( const Event& event, string process);
   // Function to check if the particle event[iPos] matches any of
   // the stored outgoing particles of the hard subprocess
   virtual bool matchesAnyOutgoing(int iPos, const Event& event);
   // Function to check if instead of the particle event[iCandidate], another
   // particle could serve as part of the hard process. Assumes that iCandidate
   // is already stored as part of the hard process.
   virtual bool findOtherCandidates(int iPos, const Event& event,
     bool doReplace);
   // Function to exchange a stored hard process candidate with another choice.
   virtual bool exchangeCandidates( vector<int> candidates1,
     vector<int> candidates2,
     unordered_map<int,int> further1, unordered_map<int,int> further2);
 
   // Function to get the number of coloured final state partons in the
   // hard process
   int nQuarksOut();
   // Function to get the number of uncoloured final state particles in the
   // hard process
   int nLeptonOut();
   // Function to get the number of electroweak final state bosons in the
   // hard process
   int nBosonsOut();
 
   // Function to get the number of coloured initial state partons in the
   // hard process
   int nQuarksIn();
   // Function to get the number of uncoloured initial state particles in the
   // hard process
   int nLeptonIn();
   // Function to report if a resonace decay was found in the 2->2 sub-process
   // of the  current state
   int hasResInCurrent();
   // Function to report the number of resonace decays in the 2->2 sub-process
   // of the  current state
   int nResInCurrent();
   // Function to report if a resonace decay was found in the 2->2 hard process
   bool hasResInProc();
   // Function to print the hard process (for debug)
   void list() const;
   // Function to print the hard process candidates in the
   // Matrix element state (for debug)
   void listCandidates() const;
 
 };
 
 //==========================================================================
 
 // MergingHooks is base class for user input to the merging procedure.
 
 class MergingHooks : public PhysicsBase {
 
 public:
 
   // Constructor.
   MergingHooks() : useShowerPluginSave(), showers(),
     doUserMergingSave(false),
     doMGMergingSave(false),
     doKTMergingSave(false),
     doPTLundMergingSave(false),
     doCutBasedMergingSave(false),
     doDynamicMergingSave(false), includeMassiveSave(),
     enforceStrongOrderingSave(),
     orderInRapiditySave(), pickByFullPSave(), pickByPoPT2Save(),
     includeRedundantSave(), pickBySumPTSave(), allowColourShufflingSave(),
     resetHardQRenSave(), resetHardQFacSave(), unorderedScalePrescipSave(),
     unorderedASscalePrescipSave(), unorderedPDFscalePrescipSave(),
     incompleteScalePrescipSave(), ktTypeSave(), nReclusterSave(),
     nQuarksMergeSave(), nRequestedSave(), scaleSeparationFactorSave(),
     nonJoinedNormSave(), fsrInRecNormSave(), herwigAcollFSRSave(),
     herwigAcollISRSave(), pT0ISRSave(), pTcutSave(),
     doNL3TreeSave(false),
     doNL3LoopSave(false),
     doNL3SubtSave(false),
     doUNLOPSTreeSave(false),
     doUNLOPSLoopSave(false),
     doUNLOPSSubtSave(false),
     doUNLOPSSubtNLOSave(false),
     doUMEPSTreeSave(false),
     doUMEPSSubtSave(false),
     doEstimateXSection(false),
     doRuntimeAMCATNLOInterfaceSave(false),
     applyVeto(),
     doRemoveDecayProducts(false), muMISave(), kFactor0jSave(), kFactor1jSave(),
     kFactor2jSave(), tmsValueSave(), tmsValueNow(),
     DparameterSave(), SparameterSave(),
     nJetMaxSave(), nJetMaxNLOSave(),
     doOrderHistoriesSave(true),
     doCutOnRecStateSave(false),
     doWeakClusteringSave(false),
     doSQCDClusteringSave(false), muFSave(), muRSave(), muFinMESave(),
     muRinMESave(),
     doIgnoreEmissionsSave(true),
     doIgnoreStepSave(true), pTsave(), weightCKKWL1Save(), weightCKKWL2Save(),
     nMinMPISave(), weightCKKWLSave(), weightFIRSTSave(),
     doVariations(false), nWgts(0), nJetMaxLocal(), nJetMaxNLOLocal(),
     hasJetMaxLocal(false),
     includeWGTinXSECSave(false), nHardNowSave(), nJetNowSave(),
     tmsHardNowSave(), tmsNowSave() {
       inputEvent = Event(); resonances.resize(0);
       useOwnHardProcess = false; hardProcess = 0; stopScaleSave= 0.0;
       nVetoedInMainShower = 0;}
 
   // Make History class friend to allow access to advanced switches
   friend class History;
   // Make Pythia class friend
   friend class Pythia;
   // Make PartonLevel class friend
   friend class PartonLevel;
   // Make SpaceShower class friend
   friend class SpaceShower;
   // Make TimeShower class friend
   friend class TimeShower;
   // Make Merging class friend
   friend class Merging;
 
   // Destructor.
   virtual ~MergingHooks();
   // Function encoding the functional definition of the merging scale
   virtual double tmsDefinition( const Event& event){ return event[0].e();}
   // Function to dampen weights calculated from histories with lowest
   // multiplicity reclustered events that do not pass the ME cuts
   virtual double dampenIfFailCuts( const Event& inEvent ) {
     // Dummy statement to avoid compiler warnings
     if(false) cout << inEvent[0].e();
     return 1.;
   }
   // Hooks to disallow states in the construction of all histories, e.g.
   // because jets are below the merging scale or fail the matrix element cuts
   // Function to allow interference in the construction of histories
   virtual bool canCutOnRecState() { return doCutOnRecStateSave; }
   // Function to check reclustered state while generating all possible
   // histories
   // Function implementing check of reclustered events while constructing
   // all possible histories
   virtual bool doCutOnRecState( const Event& event ) {
     // Dummy statement to avoid compiler warnings.
     if(false) cout << event[0].e();
     // Count number of final state partons.
     int nPartons = 0;
     for( int i=0; i < int(event.size()); ++i)
       if(  event[i].isFinal()
         && (event[i].isGluon() || event[i].isQuark()) )
         nPartons++;
     // For gg -> h, allow only histories with gluons in initial state
     if( hasEffectiveG2EW() && nPartons < 2){
       if(event[3].id() != 21 && event[4].id() != 21)
         return true;
     }
     return false;
   }
   // Function to allow not counting a trial emission.
   virtual bool canVetoTrialEmission() { return false;}
   // Function to check if trial emission should be rejected.
   virtual bool doVetoTrialEmission( const Event&, const Event& ) {
     return false; }
 
   // Function to calculate the hard process matrix element.
   virtual double hardProcessME( const Event& inEvent ) {
     // Dummy statement to avoid compiler warnings.
     if ( false ) cout << inEvent[0].e();
     return 1.; }
 
   // Functions for internal use inside Pythia source code
   // Initialize.
   virtual void init();
 
   // Function returning the value of the merging scale.
   double tms() {
     if(doCutBasedMergingSave) return 0.;
     //else return tmsValueSave;
     else return tmsValueNow;
   }
   double tmsCut() {
     if (doCutBasedMergingSave) return 0.;
     if (doDynamicMergingSave) {
       // Fetch fixed merging cut and factorisation scale.
       const double QbarCut = tmsValueSave;
       const double Q2      = infoPtr->Q2DIS();
       // Calculate dynamic merging scale, cf. eq. (2) in arXiv:0912.3715.
       return QbarCut/sqrt(1. + pow2(QbarCut/SparameterSave)/Q2);
     }
     return tmsValueSave;
   }
   void tms( double tmsIn ) { tmsValueNow = tmsIn; }
 
   // Function returning the value of the Delta R_{ij} cut for
   // cut based merging scale definition.
   double dRijMS() {
     return ((tmsListSave.size() == 3) ? tmsListSave[0] : 0.);
   }
   // Function returning the value of the pT_{i} cut for
   // cut based merging scale definition.
   double pTiMS() {
     return ((tmsListSave.size() == 3) ? tmsListSave[1] : 0.);
   }
   // Function returning the value of the pT_{i} cut for
   // cut based merging scale definition.
   double QijMS() {
     return ((tmsListSave.size() == 3) ? tmsListSave[2] : 0.);
   }
   // Function returning the value of the maximal number of merged jets.
   int nMaxJets() { return (hasJetMaxLocal) ? nJetMaxLocal : nJetMaxSave;}
   // Function returning the value of the maximal number of merged jets,
   // for which NLO corrections are available.
   int nMaxJetsNLO()
     { return (hasJetMaxLocal) ? nJetMaxNLOLocal : nJetMaxNLOSave;}
   // Function to return hard process string.
   string getProcessString() { return processNow;}
   // Function to return the number of outgoing partons in the core process
   int nHardOutPartons(){ return hardProcess->nQuarksOut();}
   // Function to return the number of outgoing leptons in the core process
   int nHardOutLeptons(){ return hardProcess->nLeptonOut();}
   // Function to return the number of outgoing electroweak bosons in the core
   // process.
   int nHardOutBosons(){ return hardProcess->nBosonsOut();}
   // Function to return the number of incoming partons (hadrons) in the core
   // process.
   int nHardInPartons(){ return hardProcess->nQuarksIn();}
   // Function to return the number of incoming leptons in the core process.
   int nHardInLeptons(){ return hardProcess->nLeptonIn();}
   // Function to report the number of resonace decays in the 2->2 sub-process
   // of the  current state.
   int nResInCurrent(){ return hardProcess->nResInCurrent();}
   // Function to determine if user defined merging should be applied.
   bool doUserMerging(){ return doUserMergingSave;}
   // Function to determine if automated MG/ME merging should be applied.
   bool doMGMerging() { return doMGMergingSave;}
   // Function to determine if KT merging should be applied.
   bool doKTMerging() { return doKTMergingSave;}
   // Function to determine if PTLund merging should be applied.
   bool doPTLundMerging() { return doPTLundMergingSave;}
   // Function to determine if cut based merging should be applied.
   bool doCutBasedMerging() { return doCutBasedMergingSave;}
   // Function to determine if merging with dynamic scale should be applied.
   bool doDynamicMerging() { return doDynamicMergingSave;}
   bool doCKKWLMerging() { return (doUserMergingSave || doMGMergingSave
       || doKTMergingSave || doPTLundMergingSave || doCutBasedMergingSave
       || doDynamicMergingSave); }
   // Functions to determine if and which part of  UMEPS merging
   // should be applied
   bool doUMEPSTree() { return doUMEPSTreeSave;}
   bool doUMEPSSubt() { return doUMEPSSubtSave;}
   bool doUMEPSMerging() { return (doUMEPSTreeSave || doUMEPSSubtSave);}
   // Functions to determine if and which part of  NL3 merging
   // should be applied
   bool doNL3Tree() { return doNL3TreeSave;}
   bool doNL3Loop() { return doNL3LoopSave;}
   bool doNL3Subt() { return doNL3SubtSave;}
   bool doNL3Merging() { return (doNL3TreeSave || doNL3LoopSave
                              || doNL3SubtSave); }
   // Functions to determine if and which part of UNLOPS merging
   // should be applied
   bool doUNLOPSTree() { return doUNLOPSTreeSave;}
   bool doUNLOPSLoop() { return doUNLOPSLoopSave;}
   bool doUNLOPSSubt() { return doUNLOPSSubtSave;}
   bool doUNLOPSSubtNLO() { return doUNLOPSSubtNLOSave;}
   bool doUNLOPSMerging() { return (doUNLOPSTreeSave || doUNLOPSLoopSave
                              || doUNLOPSSubtSave || doUNLOPSSubtNLOSave); }
 
   // Function to determine if we have a runtime interface to aMC@NLO.
   bool doRuntimeAMCATNLOInterface() { return doRuntimeAMCATNLOInterfaceSave;}
 
   // Return the number clustering steps that have actually been done.
   int nRecluster() { return nReclusterSave;}
 
   // Return number of requested additional jets on top of the Born process.
   int nRequested() { return nRequestedSave;}
 
   //----------------------------------------------------------------------//
   // Output functions to analyse/prepare event for merging
   //----------------------------------------------------------------------//
 
   // Function to check if event contains an emission not present in the hard
   // process.
   bool isFirstEmission(const Event& event);
 
   // Function to allow effective gg -> EW boson couplings.
   bool hasEffectiveG2EW() {
     if ( getProcessString().compare("pp>h") == 0 ) return true;
     return false; }
 
   // Function to allow effective gg -> EW boson couplings.
   bool allowEffectiveVertex( vector<int> in, vector<int> out) {
     if ( getProcessString().compare("ta+ta->jj") == 0
       || getProcessString().compare("ta-ta+>jj") == 0 ) {
       int nInFermions(0), nOutFermions(0);
       for (int i=0; i < int(in.size()); ++i)
         if (abs(in[i])<20) nInFermions++;
       for (int i=0; i < int(out.size()); ++i)
         if (abs(out[i])<20) nOutFermions++;
       return (nInFermions%2==0 && nOutFermions%2==0);
     }
     return false;
   }
 
   // Return event stripped from decay products.
   Event bareEvent( const Event& inputEventIn, bool storeInputEvent );
   // Write event with decay products attached to argument.
   bool reattachResonanceDecays( Event& process );
 
   // Check if particle at position iPos is part of the hard sub-system
   bool isInHard( int iPos, const Event& event);
 
   // Function to return the number of clustering steps for the current event
   virtual int getNumberOfClusteringSteps(const Event& event,
     bool resetNjetMax = false);
 
   //----------------------------------------------------------------------//
   // Functions to steer construction of histories
   //----------------------------------------------------------------------//
 
   // Function to force preferred picking of ordered histories. By default,
   // unordered histories will only be considered if no ordered histories
   // were found.
   void orderHistories( bool doOrderHistoriesIn) {
     doOrderHistoriesSave = doOrderHistoriesIn; }
   // Function to force cut on reconstructed states internally, as needed
   // for gg -> Higgs to ensure that e.g. uu~ -> Higgs is not constructed.
   void allowCutOnRecState( bool doCutOnRecStateIn) {
     doCutOnRecStateSave = doCutOnRecStateIn; }
 
   // Function to allow final state clusterings of weak bosons
   void doWeakClustering( bool doWeakClusteringIn ) {
     doWeakClusteringSave = doWeakClusteringIn; }
 
   //----------------------------------------------------------------------//
   // Functions used as default merging scales
   //----------------------------------------------------------------------//
 
   // Function to check if the input particle is a light jet, i.e. should be
   // checked against the merging scale defintion.
   bool checkAgainstCut( const Particle& particle);
   // Function to return the value of the merging scale function in the
   // current event.
   virtual double tmsNow( const Event& event );
   // Find the minimal Lund pT between coloured partons in the event
   double rhoms( const Event& event, bool withColour);
   // Function to calculate the minimal kT in the event
   double kTms(const Event & event);
   // Find the if the event passes the Delta R_{ij}, pT_{i} and Q_{ij} cuts on
   // the matrix element, as needed for cut-based merging scale definition
   double cutbasedms( const Event& event );
 
   //----------------------------------------------------------------------//
   // Functions to steer shower evolution (public to allow for PS plugin)
   //----------------------------------------------------------------------//
 
   // Flag to indicate trial shower usage.
   void doIgnoreEmissions( bool doIgnoreIn ) {
     doIgnoreEmissionsSave = doIgnoreIn;}
   // Function to allow not counting a trial emission.
   virtual bool canVetoEmission() { return !doIgnoreEmissionsSave; }
   // Function to check if emission should be rejected.
   virtual bool doVetoEmission( const Event& );
 
   //----------------------------------------------------------------------//
   // Functions used as clusterings / probabilities
   //----------------------------------------------------------------------//
 
   bool useShowerPluginSave;
   virtual bool useShowerPlugin() { return useShowerPluginSave; }
   virtual bool usesVincia() {return false;}
 
   //----------------------------------------------------------------------//
   // Functions to retrieve if merging weight should countin the internal
   // cross section and the event weight.
   //----------------------------------------------------------------------//
 
   bool includeWGTinXSEC() { return includeWGTinXSECSave;}
 
   //----------------------------------------------------------------------//
   // Functions to retrieve event veto information
   //----------------------------------------------------------------------//
 
   int nHardNow()      { return nHardNowSave; }
   double tmsHardNow() { return tmsHardNowSave; }
   int nJetsNow()      { return nJetNowSave; }
   double tmsNow()     { return tmsNowSave;}
 
   void setHardProcessPtr(HardProcess* hardProcIn) { hardProcess = hardProcIn; }
 
   //----------------------------------------------------------------------//
   // Functions related to renormalization scale variations
   //----------------------------------------------------------------------//
 
   int nMuRVar() { return muRVarFactors.size(); }
   void printIndividualWeights();
 
   //----------------------------------------------------------------------//
   // The members, switches etc.
   //----------------------------------------------------------------------//
 
   // Helper class doing all the core process book-keeping
   bool useOwnHardProcess;
   HardProcess* hardProcess;
 
   PartonLevel* showers;
   void setShowerPointer(PartonLevel* psIn ) {showers = psIn;}
 
   // AlphaS objects for alphaS reweighting use
   AlphaStrong AlphaS_FSRSave;
   AlphaStrong AlphaS_ISRSave;
   AlphaEM AlphaEM_FSRSave;
   AlphaEM AlphaEM_ISRSave;
 
   // Saved path to LHE file for more automated merging
   string lheInputFile;
 
   // Flags for merging procedure definition.
   bool   doUserMergingSave, doMGMergingSave, doKTMergingSave,
          doPTLundMergingSave, doCutBasedMergingSave, doDynamicMergingSave,
          includeMassiveSave, enforceStrongOrderingSave, orderInRapiditySave,
          pickByFullPSave, pickByPoPT2Save, includeRedundantSave,
          pickBySumPTSave, allowColourShufflingSave, resetHardQRenSave,
          resetHardQFacSave;
   int    unorderedScalePrescipSave, unorderedASscalePrescipSave,
          unorderedPDFscalePrescipSave, incompleteScalePrescipSave,
          ktTypeSave, nReclusterSave, nQuarksMergeSave, nRequestedSave;
 
   double scaleSeparationFactorSave, nonJoinedNormSave,
          fsrInRecNormSave, herwigAcollFSRSave, herwigAcollISRSave,
          pT0ISRSave, pTcutSave, pTminISRSave, pTminFSRSave;
   bool   doNL3TreeSave, doNL3LoopSave, doNL3SubtSave;
   bool   doUNLOPSTreeSave, doUNLOPSLoopSave, doUNLOPSSubtSave,
          doUNLOPSSubtNLOSave;
   bool   doUMEPSTreeSave, doUMEPSSubtSave;
 
   // Flag to only do phase space cut, rejecting events below the tms cut.
   bool   doEstimateXSection;
 
   // Flag for runtime aMC@NLO interface. Needed for aMC@NLO-Delta.
   bool   doRuntimeAMCATNLOInterfaceSave;
 
   // Flag for postponing event vetos. If false, events are not vetoed
   // based on the merging scale in CKKW-L merging, but have to be
   // vetoed by the user in the main program.
   bool   applyVeto;
 
   // Save input event in case decay products need to be detached.
   Event inputEvent;
   vector< pair<int,int> > resonances;
   bool doRemoveDecayProducts;
 
   // Starting scale for attaching MPI.
   double muMISave;
 
   // Precalculated K-factors.
   double kFactor0jSave;
   double kFactor1jSave;
   double kFactor2jSave;
 
   // Saved members.
   double tmsValueSave, tmsValueNow, DparameterSave, SparameterSave;
   int nJetMaxSave;
   int nJetMaxNLOSave;
 
   string processSave, processNow;
 
   // List of cut values to used to define a merging scale. Ordering:
   // 0: DeltaR_{jet_i,jet_j,min}
   // 1: p_{T,jet_i,min}
   // 2: Q_{jet_i,jet_j,min}
   vector<double> tmsListSave;
 
   // INTERNAL Hooks to allow construction of all histories,
   // including un-ordered ones
   bool doOrderHistoriesSave;
 
   // INTERNAL Hooks to disallow states in the construction of all histories,
   // e.g. because jets are below the merging scale, of to avoid the
   // construction of uu~ -> Higgs histories.
   bool doCutOnRecStateSave;
 
   // INTERNAL Hooks to allow clustering W bosons.
   bool doWeakClusteringSave, doSQCDClusteringSave;
 
   // Store / get first scale in PDF's that Pythia should have used
   double muFSave;
   double muRSave;
 
   // Store / get factorisation scale used in matrix element calculation.
   double muFinMESave;
   double muRinMESave;
 
   // Flag to indicate trial shower usage.
   bool doIgnoreEmissionsSave;
   // Flag to indicate if events should be vetoed.
   bool doIgnoreStepSave;
   // Stored weights in case veot needs to be revoked
   double pTsave;
   vector<double> weightCKKWL1Save, weightCKKWL2Save;
   int nMinMPISave;
   // Save CKKW-L weight / O(\alpha_s) weight.
   vector<double> weightCKKWLSave, weightFIRSTSave;
 
   // Struct to save individual weights
   struct IndividualWeights {
     vector<double> wtSave;
     vector<double> pdfWeightSave;
     vector<double> mpiWeightSave;
     vector<double> asWeightSave;
     vector<double> aemWeightSave;
     vector<double> bornAsVarFac;
   };
 
   IndividualWeights individualWeights;
 
   // Flag to indicate whether renormalization scale variations are performed
   bool doVariations;
   // Vector of variation factors applied to renormalization scale
   vector<double> muRVarFactors;
   // Number of weights, nominal + variations
   int nWgts;
 
   // Local copies of nJetMax inputs, if recalculation is necessary.
   int nJetMaxLocal;
   int nJetMaxNLOLocal;
   bool hasJetMaxLocal;
 
   // Event veto and hard process information, if veto should not applied be
   // directly, but is up to the user.
   bool includeWGTinXSECSave;
   int nHardNowSave, nJetNowSave;
   double tmsHardNowSave, tmsNowSave;
 
   //----------------------------------------------------------------------//
   // Generic setup functions
   //----------------------------------------------------------------------//
 
   // Function storing candidates for the hard process in the current event
   // Needed in order not to cluster members of the core process
   void storeHardProcessCandidates(const Event& event){
     hardProcess->storeCandidates(event,getProcessString());
   }
 
   // Function to set the path to the LHE file, so that more automated merging
   // can be used.
   // Remove "_1.lhe" suffix from LHE file name.
   // This is done so that the HarsProcess class can access both the +0 and +1
   // LHE files to find both the merging scale and the core process string
   // Store.
   void setLHEInputFile( string lheFile) {
     lheInputFile = lheFile.substr(0,lheFile.size()-6); }
 
   //----------------------------------------------------------------------//
   // Functions for output of class members.
   //----------------------------------------------------------------------//
 
   // Return AlphaStrong objects
   AlphaStrong* AlphaS_FSR() { return &AlphaS_FSRSave;}
   AlphaStrong* AlphaS_ISR() { return &AlphaS_ISRSave;}
   AlphaEM* AlphaEM_FSR() { return &AlphaEM_FSRSave;}
   AlphaEM* AlphaEM_ISR() { return &AlphaEM_ISRSave;}
 
   // Functions to return advanced merging switches
   // Include masses in definition of evolution pT and splitting kernels
   bool includeMassive() { return includeMassiveSave;}
   // Prefer strongly ordered histories
   bool enforceStrongOrdering() { return enforceStrongOrderingSave;}
   // Prefer histories ordered in rapidity and evolution pT
   bool orderInRapidity() { return orderInRapiditySave;}
   // Pick history probabilistically by full (correct) splitting probabilities
   bool pickByFull() { return pickByFullPSave;}
   // Pick history probabilistically, with easier form of probabilities
   bool pickByPoPT2() { return pickByPoPT2Save;}
   // Include redundant terms (e.g. PDF ratios) in the splitting probabilities
   bool includeRedundant(){ return includeRedundantSave;}
   // Pick by winner-takes-it-all, with minimum sum of scalar evolution pT
   bool pickBySumPT(){ return pickBySumPTSave;}
 
   // Prescription for combined scale of unordered emissions
   // 0 : use larger scale
   // 1 : use smaller scale
   int unorderedScalePrescip() { return unorderedScalePrescipSave;}
   // Prescription for combined scale used in alpha_s for unordered emissions
   // 0 : use combined emission scale in alpha_s weight for both (!) splittings
   // 1 : use original reclustered scales of each emission in alpha_s weight
   int unorderedASscalePrescip() { return unorderedASscalePrescipSave;}
   // Prescription for combined scale used in PDF ratios for unordered
   // emissions
   // 0 : use combined emission scale in PDFs for both (!) splittings
   // 1 : use original reclustered scales of each emission in PDF ratiost
   int unorderedPDFscalePrescip() { return unorderedPDFscalePrescipSave;}
   // Prescription for starting scale of incomplete histories
   // 0: use factorization scale
   // 1: use sHat
   // 2: use s
   int incompleteScalePrescip() { return incompleteScalePrescipSave;}
 
   // Allow swapping one colour index while reclustering
   bool allowColourShuffling() { return allowColourShufflingSave;}
 
   // Allow use of dynamical renormalisation scale of the core 2-> 2 process.
   bool resetHardQRen() { return resetHardQRenSave; }
   // Allow use of dynamical factorisation scale of the core 2-> 2 process.
   bool resetHardQFac() { return resetHardQFacSave; }
 
   // Factor by which two scales should differ to be classified strongly
   // ordered.
   double scaleSeparationFactor() { return scaleSeparationFactorSave;}
   // Absolute normalization of splitting probability for non-joined
   // evolution.
   double nonJoinedNorm() { return nonJoinedNormSave;}
   // Absolute normalization of splitting probability for final state
   // splittings with initial state recoiler
   double fsrInRecNorm() { return fsrInRecNormSave;}
   // Factor multiplying scalar evolution pT for FSR splitting, when picking
   // history by minimum scalar pT (see Jonathan Tully's thesis)
   double herwigAcollFSR() { return herwigAcollFSRSave;}
   // Factor multiplying scalar evolution pT for ISR splitting, when picking
   // history by minimum scalar pT (see Jonathan Tully's thesis)
   double herwigAcollISR() { return herwigAcollISRSave;}
   // ISR regularisation scale
   double pT0ISR() { return pT0ISRSave;}
   // Shower cut-off scale
   double pTcut() { return pTcutSave;}
 
   // MI starting scale.
   void muMI( double mu) { muMISave = mu; }
   double muMI() { return muMISave;}
 
   // Full k-Factor for current event
   double kFactor(int njet = 0) {
     return (njet == 0) ? kFactor0jSave
           :(njet == 1) ? kFactor1jSave
           : kFactor2jSave;
   }
   // O(\alhpa_s)-term of the k-Factor for current event
   double k1Factor( int njet = 0) {
     return (kFactor(njet) - 1)/infoPtr->alphaS();
   }
 
   // Function to return if construction of histories is biased towards ordered
   // histories.
   bool orderHistories() { return doOrderHistoriesSave;}
 
   // INTERNAL Hooks to disallow states in the construction of all histories,
   // e.g. because jets are below the merging scale, of to avoid the
   // construction of uu~ -> Higgs histories.
   bool allowCutOnRecState() { return doCutOnRecStateSave;}
 
   // INTERNAL Hooks to allow clustering W bosons.
   bool doWeakClustering() { return doWeakClusteringSave;}
   // INTERNAL Hooks to allow clustering clustering of gluons to squarks.
   bool doSQCDClustering() { return doSQCDClusteringSave;}
 
   // Store / get first scale in PDF's that Pythia should have used
   double muF() { return (muFSave > 0.) ? muFSave : infoPtr->QFac();}
   double muR() { return (muRSave > 0.) ? muRSave : infoPtr->QRen();}
   // Store / get factorisation scale used in matrix element calculation.
   double muFinME() {
     // Start with checking the event attribute called "muf".
     string mus = infoPtr->getEventAttribute("muf2",true);
     double mu  = (mus.empty()) ? 0. : atof((char*)mus.c_str());
     mu = sqrt(mu);
     // Check the scales tag of the event.
     if (infoPtr->scales) mu = infoPtr->getScalesAttribute("muf");
     return (mu > 0.) ? mu : (muFinMESave > 0.) ? muFinMESave
       : infoPtr->QFac();
   }
   double muRinME() {
     // Start with checking the event attribute called "mur2".
     string mus = infoPtr->getEventAttribute("mur2",true);
     double mu  = (mus.empty()) ? 0. : atof((char*)mus.c_str());
     mu = sqrt(mu);
     // Check the scales tag of the event.
     if (infoPtr->scales) mu = infoPtr->getScalesAttribute("mur");
     return (mu > 0.) ? mu : (muRinMESave > 0.) ? muRinMESave
       : infoPtr->QRen();
   }
 
 
   //----------------------------------------------------------------------//
   // Functions to steer merging code
   //----------------------------------------------------------------------//
 
   // Flag to indicate if events should be vetoed.
   void doIgnoreStep(bool doIgnoreIn) {doIgnoreStepSave = doIgnoreIn;}
   // Function to allow event veto.
   virtual bool canVetoStep() {return !doIgnoreStepSave;}
 
   // Stored weights in case veto needs to be revoked
   void storeWeights(vector<double> weight) {
     weightCKKWL1Save = weightCKKWL2Save = weight;}
 
   // Function to check event veto.
   virtual bool doVetoStep(const Event& process, const Event& event,
     bool doResonance = false);
 
   // Set starting scales
   virtual bool setShowerStartingScales( bool isTrial, bool doMergeFirstEmm,
     double& pTscaleIn, const Event& event,
     double& pTmaxFSRIn, bool& limitPTmaxFSRin,
     double& pTmaxISRIn, bool& limitPTmaxISRin,
     double& pTmaxMPIIn, bool& limitPTmaxMPIin );
 
   // Set shower stopping scale. Necessary to e.g. avoid accumulation of
   // incorrect (low-pT) shower weights through trial showering.
   double stopScaleSave;
   void setShowerStoppingScale(double scale = 0.) {stopScaleSave = scale;}
   double getShowerStoppingScale() {return stopScaleSave;}
 
   void nMinMPI(int nMinMPIIn) {nMinMPISave = nMinMPIIn; }
   int nMinMPI() {return nMinMPISave;}
 
   //----------------------------------------------------------------------//
   // Functions for internal merging scale definions
   //----------------------------------------------------------------------//
 
   // Function to calculate the kT separation between two particles
   double kTdurham(const Particle& RadAfterBranch,
     const Particle& EmtAfterBranch, int Type, double D );
   // Function to compute "pythia pT separation" from Particle input
   double rhoPythia(const Event& event, int rad, int emt, int rec,
     int ShowerType);
 
   // Function to find a colour (anticolour) index in the input event,
   // used to find colour-connected recoilers
   int findColour(int col, int iExclude1, int iExclude2,
     const Event& event, int type, bool isHardIn);
   // Function to compute Delta R separation from 4-vector input
   double deltaRij(Vec4 jet1, Vec4 jet2);
 
   //----------------------------------------------------------------------//
   // Functions for weight management
   //----------------------------------------------------------------------//
 
   // Function to get the CKKW-L weight for the current event
   double getWeightNLO(int i=0) { return (weightCKKWLSave[i]
                                          - weightFIRSTSave[i]);}
   // Return CKKW-L weight.
   vector<double> getWeightCKKWL() { return weightCKKWLSave; }
   // Return O(\alpha_s) weight.
   vector<double> getWeightFIRST() { return weightFIRSTSave; }
   // Set CKKW-L weight.
   void setWeightCKKWL( vector<double> weightIn){
     weightCKKWLSave = weightIn;
     infoPtr->weightContainerPtr
       ->weightsMerging.setValueVector(weightIn); }
   // Set O(\alpha_s) weight.
   void setWeightFIRST( vector<double> weightIn){
     weightFIRSTSave = weightIn;
     infoPtr->weightContainerPtr->weightsMerging
       .setValueFirstVector(weightIn); }
   // Function to return Sudakov weight as calculated before, also include MPI
   // weight. Only call after regular weight functions, since it is calculated
   // there.
   vector<double> getSudakovWeight() {
     vector<double> ret = individualWeights.wtSave;
     for (int i = 0; i < nWgts; ++i) {
      ret[i] *= individualWeights.pdfWeightSave[i] *
                individualWeights.mpiWeightSave[i];
     }
    return ret;
   }
   // Function to return coupling weight.
   vector<double> getCouplingWeight() {
     vector<double> ret = individualWeights.asWeightSave;
     for (int i = 0; i < nWgts; ++i) {
       ret[i] *= individualWeights.aemWeightSave[i];
     }
     return ret;
   }
 
 //--------------------------------------------------------------------------
 
 
 
   //----------------------------------------------------------------------//
   // Functions and members to store the event veto information
   //----------------------------------------------------------------------//
 
   // Set CKKWL veto information.
   void setEventVetoInfo(int nJetNowIn, double tmsNowIn) {
     nJetNowSave = nJetNowIn; tmsNowSave = tmsNowIn; }
 
   // Set the hard process information.
   void setHardProcessInfo(int nHardNowIn, double tmsHardNowIn) {
     nHardNowSave = nHardNowIn; tmsHardNowSave = tmsHardNowIn; }
 
   // Statistics.
   int nVetoedInMainShower;
   void addVetoInMainShower() {++nVetoedInMainShower;}
   int getNumberVetoedInMainShower() {return nVetoedInMainShower;}
 
 };
 
 //==========================================================================
 
 } // end namespace Pythia8
 
 #endif // Pythia8_MergingHooks_H

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