class HParticlePairMaker: public TObject

_HADES_CLASS_DESCRIPTION



 HParticlePairMaker

 Build vectors of freference candidates, fothers candidates and fpairs
 for the current event. As reference candidates marked as kIsLepton
 will be used.

 nectEvent() to be called inside eventloop after HParticleSorter selection.
 1. clear all internal structures
 2. fill vector freference by candidates which are flagged kIsLepton ( or kIsUsed if it is setup)
    All other candidates (disregarding kIsLepton or kIsUsed) are added to vector fothers
    To avoid unneeded pairs the user can set a userFilter by set setUserFilter(Bool_t (*userfilter)(HParticleCand*))
    In this case only candidates passing this function (return kTRUE) will be taken into account
    for freference and fothers.
 3. created all pair combinations between freference x freference (no double counting) and freference x fothers.
       If setDoSkippedFullCandPairs(kTRUE) is  set (default) in addition all pairs of full reconstructed
       particles ( inner+outer MDC + META) of fOthers are build (ffullrecoOthers x ffullrecoOthers +
       ffullrecoOthers x fnofullrecoOthers ). All pairs with full reco candidates of the event are build
       this way for investigation, even the ones which are skipped from reference by any criteria or double hit
       rejection.
    a. pass the selectPID1 and selectPID2 functions
       will get pid1 or pid2 assigned. Otherwise pid is -2(fake+), -1(fake-) (see HPhysicsConstants).
       if pid2 fails it will get pid assigned opposite to reference cand in pairCase10.
       fakes for pid2 will be assigned by polarity or opposite to reference cand.
    b. eClosePairSelect flags will be set for each pair (see hparticledef.h).
       This flags can be used later to classify the pairs.
    c. pairs are inserted in fpairs vector. With static HParticlePair::setDoMomentumCorrection(Bool_t doit)
       the enegryloss correction can be swithced on/off
    d. secondary vertex and vertex cut vars are calulated. Which  primary ebevnt vertex
       should be used has to be set by the user (default = kVertexParticle, see eVertex
       in hparticledef.h). The user can provide an own event vertex per event by calling setVertex().


 Bool_t  HParticleTool::evalPairsFlags(UInt_t flag,HParticlePair& pair)
 can be used to classify the pair according to the predefined pair cases
 in ePairCase + eClosePairSelect (hparticledef.h). There are dedicated filter
 functions provided to select from the pairs vector

   Fig 1. All predefined pairCases for Leptons

   Fig 2. All predefined pairCases for Hadrons

   Fig 2. All predefined pairCases for mixed Lepton Hadrons



 USAGE:
 #include  "hparticlepairmaker.h"
 #include  "hparticledef.h"
 #include  "hparticletool.h"
 #include  <vector>
 using namespace std;



 {
 // setup HLoop etc ....


  HEnergyLossCorrPar enLossCorr;
  enLossCorr.setDefaultPar("apr12"); //  "jan04","nov02","aug04","apr12"

 //---------------------------------------------
 // HPARTICLEPAIRMAKER SETUP :
 HParticlePairMaker pairmaker;
 // pairmaker.setPIDs(2,3,51) // default
 // pairmaker.setPIDsSelection(mySelectionPID1,mySelectionPID2) // set your own selection function for pid1+pid2 (signature :  Bool_t myfunction(HParticleCand*) )
 // pairmaker.setUseLeptons(kTRUE);// kTRUE : use kIsLepton, kFALSE: kIsUsed for selection of reference  (default kTRUE)
 // pairmake.setRequireRich(kFALSE); // do not ask for rich Hit in selection functions ( default = kTRUE)
 // pairmaker.setVertexCase(Particle::kVertexParticle); // select which event vertex to use (default = kVertexParticle)
 // HParticlePair::setDoMomentumCorrection(kTRUE); // default : kTRUE
 //---------------------------------------------

 vector<HParticlePair*> pairs;

 for (Int_t i=0; i < entries; i++) {
    Int_t nbytes =  loop.nextEvent(i);             // get next event. categories will be cleared before
    if(nbytes <= 0) { cout<<nbytes<<endl; break; } // last event reached


    //--------------------------------------------------------------------------
    // HPARTICLETRACKSORTER SETUP
    sorter.cleanUp();
    sorter.resetFlags(kTRUE,kTRUE,kTRUE,kTRUE);     // reset all flags for flags (0-28) ,reject,used,lepton
    Int_t nCandLep     = sorter.fill(HParticleTrackSorter::selectLeptons);   // fill only good leptons
    Int_t nCandLepBest = sorter.selectBest(HParticleTrackSorter::kIsBestRKRKMETA,HParticleTrackSorter::kIsLepton);
    Int_t nCandHad     = sorter.fill(HParticleTrackSorter::selectHadrons);   // fill only good hadrons (already marked good leptons will be skipped)
    Int_t nCandHadBest = sorter.selectBest(HParticleTrackSorter::kIsBestRKRKMETA,HParticleTrackSorter::kIsHadron);
    //--------------------------------------------------------------------------


    //###########################################################################
    // HPARTICLEPAIRMAKER ACTION:
    pairmaker.nextEvent();  // call it after your HParticleSorter action!



    //--------------------------------------------------------------------------
    // example  1:
    // fill list of pairs for pairCase1 and require
    // fitted inner+out+RK for second leg in addition
    pairmaker.filterPairsVector(pairs,kPairCase1|kFittedInnerMDC2|kFittedInnerMDC2|kRK2);

    for(UInt_t j = 0; j < pairs.size(); j++ ){ // print the pairs
       pairs[j]->print();
    }
    //--------------------------------------------------------------------------


    //--------------------------------------------------------------------------
    // example 2:
    // get list of all pairs and loop over the list
    // plot different pairCases

    vector<HParticlePair>& pairsVec =  pairmaker.getPairsVector();
    for(UInt_t l = 0; l < pairsVec.size(); l++ ){
        HParticlePair& pair = pairsVec[l];

        if(HParticleTool::evalPairsFlags(kPairCase1,pair)){
    	cout<<"case1"<<endl;
        } else if(HParticleTool::evalPairsFlags(kPairCase2,pair)){
    	cout<<"case2"<<endl;
        } else if(HParticleTool::evalPairsFlags(kPairCase3,pair)){
    	cout<<"case3"<<endl;
        } else if(HParticleTool::evalPairsFlags(kPairCase4,pair)){
    	cout<<"case4"<<endl;
        } else if(HParticleTool::evalPairsFlags(kPairCase5,pair)){
    	cout<<"case5"<<endl;
        } else if(HParticleTool::evalPairsFlags(kPairCase6,pair)){
    	cout<<"case6"<<endl;
        } else if(HParticleTool::evalPairsFlags(kPairCase7,pair)){
    	cout<<"case7"<<endl;
        } else if(HParticleTool::evalPairsFlags(kPairCase8,pair)){
    	cout<<"case8"<<endl;
        } else if(HParticleTool::evalPairsFlags(kPairCase9,pair)){
    	cout<<"case9"<<endl;
        } else if(HParticleTool::evalPairsFlags(kPairCase10,pair)){
    	cout<<"case10"<<endl;
        } else if(HParticleTool::evalPairsFlags(kPairCase11,pair)){
   	cout<<"case11"<<endl;
        }
    }
    //--------------------------------------------------------------------------
    //###########################################################################
   }  // end event loop
 }