MergeMcEventCollTool.cxx

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/*
  Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
*/
 
#include "MergeMcEventCollTool.h"
 
#include "AthenaKernel/errorcheck.h" // Handy definitions for error checking
#include "GeneratorObjects/McEventCollection.h"
#include "PileUpTools/PileUpMergeSvc.h"
#include "TruthUtils/HepMCHelpers.h"
 
#include "GaudiKernel/PhysicalConstants.h"
using namespace Gaudi::Units;
 
 
#include <vector>
#include <string>
#include <cmath>
#include <stdexcept>
#include <array>
 
typedef std::pair<int, int> IndexKey;
namespace {
  IndexKey makekey(int signal_process_id, int event_number, int separator_hack=0) {
    //std::size_t key(0);
    //Check for Separtor GenEvents
    if(signal_process_id==0 && event_number==-1) {
      return std::make_pair(separator_hack, event_number);
    }
    return std::make_pair(signal_process_id, event_number);
  }
 
  class GenEventSorter {
  public:
    typedef std::map<IndexKey, int> PileUpBackgroundMap;
    GenEventSorter(const PileUpBackgroundMap& backgroundClassificationMap) : m_backgroundClassificationMap(backgroundClassificationMap) {}
    bool operator() (const HepMC::GenEvent *pGenEvent1, const HepMC::GenEvent *pGenEvent2) {
      const int signal_process_id1(HepMC::signal_process_id(pGenEvent1)), event_number1(pGenEvent1->event_number()), separator_hack1(HepMC::mpi(pGenEvent1));
      const int signal_process_id2(HepMC::signal_process_id(pGenEvent2)), event_number2(pGenEvent2->event_number()), separator_hack2(HepMC::mpi(pGenEvent2));
      const IndexKey key1(makekey(signal_process_id1, event_number1,separator_hack1));
      const IndexKey key2(makekey(signal_process_id2, event_number2,separator_hack2));
      const PileUpBackgroundMap::const_iterator event1=m_backgroundClassificationMap.find(key1);
      const PileUpBackgroundMap::const_iterator event2=m_backgroundClassificationMap.find(key2);
      if(event1==m_backgroundClassificationMap.end())  {
        throw std::runtime_error("GenEventSorter::operator() : IndexKey 1 not found in backgroundClassificationMap");
      }
      if(event2==m_backgroundClassificationMap.end())  {
        throw std::runtime_error("GenEventSorter::operator() : IndexKey 2 not found in backgroundClassificationMap");
      }
      
      //Both events have the same 'type'
      if(event1->second==event2->second) {
        if (is_separator(signal_process_id1, event_number1)) {return true;} //separator GenEvents should go at the start of each classification
        if (is_separator(signal_process_id2, event_number2)) {return false;}
        //Both events are from the same dataset
        if (signal_process_id1==signal_process_id2) {
          return (event_number1<event_number2);
        }
        return (signal_process_id1<signal_process_id2);
      }
      return (event1->second<event2->second);
 
    }
  private:
    inline bool is_separator(int signal_process_id, int event_number) const { return (0==signal_process_id && -1==event_number); }
    const PileUpBackgroundMap& m_backgroundClassificationMap;
  };
} //anonymous namespace
 
MergeMcEventCollTool::MergeMcEventCollTool(const std::string& type,
                                           const std::string& name,
                                           const IInterface *parent) :
  PileUpToolBase(type, name, parent)
{
}
 
StatusCode MergeMcEventCollTool::initialize() {
  ATH_MSG_DEBUG( "Initializing" );
  if (m_doSlimming) {
    //set all m_saveTypes based on properties
    m_saveType[INTIME] = m_saveInTimePileup.value();
    m_saveType[OUTOFTIME] = m_saveOutOfTimePileup.value();
    m_saveType[RESTOFMB] = m_saveRestOfPileup.value();
    m_saveType[CAVERN] = m_saveCavernBackground.value();
  }
  else {
    m_keepUnstable        = true;
    m_saveType[INTIME]    = true;
    m_saveType[OUTOFTIME] = true;
    m_saveType[RESTOFMB]  = true;
    m_saveType[CAVERN]    = true;
  }
  m_r2Range = m_rRange*m_rRange;
 
  return StatusCode::SUCCESS;
}
 
StatusCode MergeMcEventCollTool::prepareEvent(const EventContext& /*ctx*/, unsigned int nInputEvents) {
  //clear the background classification map
  m_backgroundClassificationMap.clear();
  m_newevent=true;
 
  //Check we are getting at least one event
  m_nInputMcEventColls = nInputEvents;
  if (0 == m_nInputMcEventColls) {
    msg(MSG::ERROR)
      << "prepareEvent: TimedTruthList with key "
      << m_truthCollInputKey.value()
      << " is empty" << endmsg;
    return StatusCode::RECOVERABLE;
  }
  ATH_MSG_DEBUG( "prepareEvent: there are " << m_nInputMcEventColls << " subevents in this event.");
 
  return StatusCode::SUCCESS;
}
 
StatusCode MergeMcEventCollTool::processAllSubEvents(const EventContext& /*ctx*/) {
  ATH_MSG_VERBOSE ( "processAllSubEvents()" );
  if(!m_pMergeSvc) {
    if (!(m_pMergeSvc.retrieve()).isSuccess()) {
      ATH_MSG_FATAL ( "processAllSubEvents: Could not find PileUpMergeSvc" );
      return StatusCode::FAILURE;
    }
  }
 
  //PRECONDITIONS
  //first get the list of McEventCollections
  typedef PileUpMergeSvc::TimedList<McEventCollection>::type TimedTruthList;
  TimedTruthList truthList;
  if (!m_pMergeSvc->retrieveSubEvtsData(m_truthCollInputKey.value(), truthList).isSuccess() ) {
    msg(MSG::ERROR)
      << "execute: Can not find TimedTruthList with key "
      << m_truthCollInputKey.value() << endmsg;
    return StatusCode::RECOVERABLE;
  }
 
  //clear the background classification map
  m_backgroundClassificationMap.clear();
 
  //Check we are getting at least one event
  m_nInputMcEventColls=truthList.size();
  if (0 == m_nInputMcEventColls) {
    msg(MSG::ERROR)
      << "execute: TimedTruthList with key "
      << m_truthCollInputKey.value()
      << " is empty" << endmsg;
    return StatusCode::RECOVERABLE;
  }
  ATH_MSG_DEBUG( "execute: there are " << m_nInputMcEventColls << " subevents in this event.");
  TimedTruthList::iterator timedTruthListIter(truthList.begin()), endOfTimedTruthList(truthList.end());
  //loop over the McEventCollections (each one assumed to containing exactly one GenEvent) of the various input events
  m_newevent=true;
  while (timedTruthListIter != endOfTimedTruthList) {
    const PileUpTimeEventIndex& currentPileUpTimeEventIndex(timedTruthListIter->first);
    const McEventCollection *pBackgroundMcEvtColl(&*(timedTruthListIter->second));
    if (!processEvent(pBackgroundMcEvtColl, currentPileUpTimeEventIndex.time(), currentPileUpTimeEventIndex.index(), static_cast<int>(currentPileUpTimeEventIndex.type())).isSuccess()) {
      ATH_MSG_ERROR ("Failed to process McEventCollection." );
      return StatusCode::FAILURE;
    }
    ++timedTruthListIter;
  } //timed colls
 
  //Remove empty copies of GenEvents
  if(m_compressOutputCollection) CHECK( compressOutputMcEventCollection() );
 
  //Sort the GenEvents in the output McEventCollection according to background classification
  std::sort(m_pOvrlMcEvColl->begin(), m_pOvrlMcEvColl->end(), GenEventSorter(m_backgroundClassificationMap));
 
  if(msgLvl(MSG::DEBUG)) {
    ATH_MSG_DEBUG("Sorted McEventCollection OK.");
    printDetailsOfMergedMcEventCollection();
  }
 
  if(m_pOvrlMcEvColl->at(0)->event_number()!=-2)
    {
      ATH_MSG_FATAL("Signal GenEvent is not first in the list! Something has gone wrong during the GenEvent sorting!");
      return StatusCode::FAILURE;
    }
  //Restore original event number
  m_pOvrlMcEvColl->at(0)->set_event_number(m_signal_event_number);
 
  return StatusCode::SUCCESS;
}
 
StatusCode MergeMcEventCollTool::processBunchXing(int bunchXing,
                                                SubEventIterator bSubEvents,
                                                SubEventIterator eSubEvents)
{
  ATH_MSG_VERBOSE ( "processBunchXing()" );
  SubEventIterator iEvt(bSubEvents);
  //loop over the McEventCollections (each one assumed to containing exactly one GenEvent) of the various input events
  while (iEvt != eSubEvents) {
    const McEventCollection *pMEC(NULL);
    if (!m_pMergeSvc->retrieveSingleSubEvtData(m_truthCollInputKey.value(), pMEC,
                           bunchXing, iEvt).isSuccess()){
      ATH_MSG_ERROR("McEventCollection not found for event key " << m_truthCollInputKey.value());
      return StatusCode::FAILURE;
    }
 
    if (!processEvent(pMEC,iEvt->time(),iEvt->index(), static_cast<int>(iEvt->type())).isSuccess()) {
      ATH_MSG_ERROR ("processBunchXing: Failed to process McEventCollection." );
      return StatusCode::FAILURE;
    }
    ++iEvt;
  }
  return StatusCode::SUCCESS;
}
 
StatusCode MergeMcEventCollTool::mergeEvent(const EventContext& /*ctx*/) {
  ATH_MSG_DEBUG( "mergeEvent" );
  if(m_nBkgEventsReadSoFar+1<m_nInputMcEventColls) {
    ATH_MSG_WARNING( "mergeEvent: Expected " << m_nInputMcEventColls << " subevents, but only saw " << m_nBkgEventsReadSoFar+1 << "! The job will probably crash now..." );
    return StatusCode::FAILURE;
  }
 
  //Remove empty copies of GenEvents
  if(m_compressOutputCollection) CHECK( compressOutputMcEventCollection() );
 
  if(m_backgroundClassificationMap.size()!=m_pOvrlMcEvColl->size()) {
    ATH_MSG_WARNING( "There are " << m_pOvrlMcEvColl->size() << " GenEvents in the McEventCollection, but " << m_backgroundClassificationMap.size() << " entries in the classification map." );
  }
  //Sort the GenEvents in the output McEventCollection according to background classification
 
  std::sort(m_pOvrlMcEvColl->begin(), m_pOvrlMcEvColl->end(), GenEventSorter(m_backgroundClassificationMap));
  ATH_MSG_DEBUG("Sorted McEventCollection OK.");
  if(msgLvl(MSG::DEBUG)) { printDetailsOfMergedMcEventCollection(); }
 
  if(m_pOvrlMcEvColl->at(0)->event_number()!=-2)
    {
      ATH_MSG_FATAL("Signal GenEvent is not first in the list! Something has gone wrong during the GenEvent sorting!");
      return StatusCode::FAILURE;
    }
  //Restore original event number
  m_pOvrlMcEvColl->at(0)->set_event_number(m_signal_event_number);
 
  return StatusCode::SUCCESS;
}
void MergeMcEventCollTool::printDetailsOfMergedMcEventCollection() const {
  if (! m_pOvrlMcEvColl->empty()) {
    ATH_MSG_INFO ( "$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$" );
    ATH_MSG_INFO ( "INTIME("<<int(INTIME)<<"), OUTOFTIME("<<int(OUTOFTIME)<<"), RESTOFMB("<<int(RESTOFMB)<<"), CAVERN("<<int(CAVERN)<<"), NOPUTYPE("<<int(NOPUTYPE)<<")" );
    ATH_MSG_INFO ( "Current OUTPUT GenEvent: " );
    auto outputEventItr = m_pOvrlMcEvColl->cbegin();
    while(outputEventItr!=m_pOvrlMcEvColl->cend()) {
      const int signal_process_id(HepMC::signal_process_id((*outputEventItr))), event_number((*outputEventItr)->event_number()), separator_hack(HepMC::mpi((*outputEventItr)));
      const IndexKey key(makekey(signal_process_id,event_number,separator_hack));
      const auto event = m_backgroundClassificationMap.find(key);
      if (event == m_backgroundClassificationMap.end()) continue;
      ATH_MSG_INFO ( "GenEvent #"<<event_number<<", signal_process_id="<<signal_process_id<<", category="<<event->second<<", number of Vertices="<<(*outputEventItr)->vertices_size() );
      ++outputEventItr;
    }
    ATH_MSG_INFO ( "$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$" );
  }
  return;
}
 
StatusCode MergeMcEventCollTool::processFirstSubEvent(const McEventCollection *pMcEvtColl) {
  StatusCode sc(StatusCode::FAILURE);
  //Assumes the first sub-event is the signal event
  m_pOvrlMcEvColl = new McEventCollection(*pMcEvtColl);
  m_signal_event_number = m_pOvrlMcEvColl->at(0)->event_number();
  m_pOvrlMcEvColl->at(0)->set_event_number(-2); //Set this to zero for the purposes of sorting. (restore after sorting).
#ifdef HEPMC3
  m_pOvrlMcEvColl->at(0)->add_attribute("BunchCrossingTime",std::make_shared<HepMC3::IntAttribute>(0));
  m_pOvrlMcEvColl->at(0)->add_attribute("PileUpType",std::make_shared<HepMC3::IntAttribute>(0));
#endif
  updateClassificationMap(HepMC::signal_process_id(m_pOvrlMcEvColl->at(0)), m_pOvrlMcEvColl->at(0)->event_number(), 0,- 1, true);
  m_newevent=false; //Now the McEventCollection and classification map are not empty this should be set to false.
  ATH_MSG_DEBUG( "execute: copied original event McEventCollection" );
  const unsigned int nBackgroundMcEventCollections(m_nInputMcEventColls-1); // -1 for original event
  // -> reserve enough space
  unsigned int outCollSize(m_pOvrlMcEvColl->size());
  if(!m_onlySaveSignalTruth) { outCollSize += nBackgroundMcEventCollections; }
  outCollSize += NOPUTYPE-1; // Adding room for the spacers
  m_pOvrlMcEvColl->resize(outCollSize);
  if(!m_onlySaveSignalTruth) { ATH_MSG_DEBUG ( "Number of input SubEvents = " << m_nInputMcEventColls ); }
  ATH_MSG_DEBUG ( "Total Size of Output McEventCollection = " << outCollSize );
 
  //now place the "separator" GenEvents. This is a hack used by clients to find/double-check where the GenEvents
  //of a given type start in the overlay McEventCollection.
 
  // For example if intime and cavern saving is enabled i.e.
  // Configurable          Variable in code         Example Value
  // SaveInTimeMinBias     m_saveType[INTIME]       true
  // SaveOutOfTimeMinBias  m_saveType[OUTOFTIME]    false
  // SaveRestOfMinBias     m_saveType[RESTOFMB]     false
  // SaveCavernBackground  m_saveType[CAVERN]       true
  //If we have two input GenEvents the output collection would look like
  //SIGNAL, INTIME0, INTIME1, SEPARATOR, SEPARATOR, SEPARATOR, CAVERN0, CAVERN1
  unsigned int currentMcEventCollectionIndex(1);
  ATH_MSG_DEBUG ( "Event Type: SIGNAL Starts at Position 0" );
  for (int type(OUTOFTIME); type<NOPUTYPE; ++type) {
    //if a type is enabled leave room to insert the events of that type, otherwise place separator immediately after
    currentMcEventCollectionIndex += 1;
    m_pOvrlMcEvColl->at(currentMcEventCollectionIndex-1) = HepMC::newGenEvent(0, -1); //pid 0 & event_number -1 flags this GenEvent as SEPARATOR
    HepMC::set_mpi(m_pOvrlMcEvColl->at(currentMcEventCollectionIndex-1),type);
    updateClassificationMap(0, -1, type, type, true);
    ATH_MSG_DEBUG ( "Placing Separator for Type: "<<type<<" at Posistion: " << currentMcEventCollectionIndex-1 );
  }
  m_startingIndexForBackground=currentMcEventCollectionIndex;
  m_nBkgEventsReadSoFar=0; //number of input events/eventcolls read so far. Used to build index of output GenEvent in ovrl McEvColl
  sc = evtStore()->record(m_pOvrlMcEvColl, m_truthCollOutputKey);//**BIG TEST**//sc=StatusCode::SUCCESS;
  ATH_MSG_DEBUG( "Starting loop on Background events ... " );
 
  return sc;
}
 
bool MergeMcEventCollTool::isTruthFiltertedMcEventCollection(const McEventCollection *pMcEvtColl) const {
  const HepMC::GenEvent* currentBackgroundEvent = *(pMcEvtColl->begin());
#ifdef HEPMC3
  if (currentBackgroundEvent->particles().size()!=1) return false;
  if (currentBackgroundEvent->particles().at(0)->pdg_id()==999) return true;
#else
  if (currentBackgroundEvent->particles_size()!=1) return false;
  if ((*(currentBackgroundEvent->particles_begin()))->pdg_id()==999) return true;
#endif
  return false;
}
 
StatusCode MergeMcEventCollTool::processEvent(const McEventCollection *pMcEvtColl, const double currentEventTime, const int currentBkgEventIndex, int pileupType) {
  ATH_MSG_VERBOSE ( "processEvent()" );
  if(m_newevent) return processFirstSubEvent(pMcEvtColl);
 
  if (pMcEvtColl->empty() || m_onlySaveSignalTruth) {
    ++m_nBkgEventsReadSoFar;
    return StatusCode::SUCCESS;
  }
  //GenEvt is there
 
  //Examine the properties of the GenEvent - if it looks like a TruthFiltered background event (contains a Geantino?!) 
  //then save the whole event as below, otherwise do the usual classification.
  if(isTruthFiltertedMcEventCollection(pMcEvtColl)) {
    if ( processTruthFilteredEvent(pMcEvtColl,  currentEventTime, currentBkgEventIndex, pileupType).isSuccess() ) {
      ++m_nBkgEventsReadSoFar;
      return StatusCode::SUCCESS;
    }
    else {
      ATH_MSG_ERROR ("Failed to process a Truth Filtered GenEvent.");
    }
  }
  else {
    if ( processUnfilteredEvent(pMcEvtColl,  currentEventTime, currentBkgEventIndex, pileupType).isSuccess() ) {
      ++m_nBkgEventsReadSoFar;
      return StatusCode::SUCCESS;
    }
    else {
      ATH_MSG_ERROR ("Failed to process an Unfiltered GenEvent.");
    }
  }
  //If we make it here something has gone wrong.
  ++m_nBkgEventsReadSoFar;
  return StatusCode::FAILURE;
}
 
StatusCode MergeMcEventCollTool::saveHeavyIonInfo(const McEventCollection *pMcEvtColl)
{
  if (m_pOvrlMcEvColl->at(0)->heavy_ion()) return StatusCode::SUCCESS;
  if (pMcEvtColl->at(0)->heavy_ion())
    {
//It should be clarified if ne wants to get a copy or the content
#ifdef HEPMC3
     HepMC::GenHeavyIonPtr hinew=std::make_shared<HepMC::GenHeavyIon>(*(pMcEvtColl->at(0)->heavy_ion()));
     m_pOvrlMcEvColl->at(0)->set_heavy_ion(std::move(hinew));
#else
      m_pOvrlMcEvColl->at(0)->set_heavy_ion(*(pMcEvtColl->at(0)->heavy_ion()));
#endif
    }
  return StatusCode::SUCCESS;
}
 
StatusCode MergeMcEventCollTool::processTruthFilteredEvent(const McEventCollection *pMcEvtColl, const double currentEventTime, const int currentBkgEventIndex, int pileupType) {
  //insert the GenEvent into the overlay McEventCollection.
  ATH_MSG_VERBOSE ( "processTruthFilteredEvent(): Event Type: " << pileupType );
  ATH_CHECK(this->saveHeavyIonInfo(pMcEvtColl));
  m_pOvrlMcEvColl->at(m_startingIndexForBackground+m_nBkgEventsReadSoFar)=new HepMC::GenEvent(**(pMcEvtColl->begin()));
  HepMC::GenEvent& currentBackgroundEvent(*(m_pOvrlMcEvColl->at(m_startingIndexForBackground+m_nBkgEventsReadSoFar)));
  HepMC::fillBarcodesAttribute(&currentBackgroundEvent);
#ifdef HEPMC3
  const int bunchCrossingTime=static_cast<int>(currentEventTime);
  currentBackgroundEvent.add_attribute("BunchCrossingTime",std::make_shared<HepMC3::IntAttribute>(bunchCrossingTime));
  currentBackgroundEvent.add_attribute("PileUpType",std::make_shared<HepMC3::IntAttribute>(pileupType));
#endif
 
  currentBackgroundEvent.set_event_number(currentBkgEventIndex);
  puType currentGenEventClassification(RESTOFMB);
  if ( std::abs(currentEventTime)<51.0 ) {
    currentGenEventClassification = ( std::abs(currentEventTime)<1.0 ) ? INTIME : OUTOFTIME;
  }
  updateClassificationMap(HepMC::signal_process_id(currentBackgroundEvent),
                          currentBackgroundEvent.event_number(),
                          0, currentGenEventClassification, true);
  return StatusCode::SUCCESS;
}
 
StatusCode MergeMcEventCollTool::processUnfilteredEvent(const McEventCollection *pMcEvtColl, const double currentEventTime, const int currentBkgEventIndex, int pileupType) {
  ATH_MSG_VERBOSE ( "processUnfilteredEvent() Event Type: " << pileupType );
  ATH_CHECK(this->saveHeavyIonInfo(pMcEvtColl));
  const HepMC::GenEvent& currentBackgroundEvent(**(pMcEvtColl->begin()));         //background event
  //handle the slimming case
  HepMC::GenVertexPtr  pCopyOfGenVertex{nullptr};
  int  spi = HepMC::signal_process_id(currentBackgroundEvent);
#ifdef HEPMC3
  if ( HepMC::signal_process_vertex(&currentBackgroundEvent) ) pCopyOfGenVertex = std::make_shared<HepMC3::GenVertex> ( HepMC::signal_process_vertex(&currentBackgroundEvent)->data() );
  //insert the GenEvent into the overlay McEventCollection.
  //for configs with pile-up truth, also need to propagate barcodes to GenEvent
  HepMC::GenEvent* evt = m_onlySaveSignalTruth ? new HepMC::GenEvent() : new HepMC::GenEvent(currentBackgroundEvent);
  const int bunchCrossingTime=static_cast<int>(currentEventTime);
  evt->add_attribute("BunchCrossingTime",std::make_shared<HepMC3::IntAttribute>(bunchCrossingTime));
  evt->add_attribute("PileUpType",std::make_shared<HepMC3::IntAttribute>(pileupType));
  //AV Not sure if one should add the vertex here
  evt->set_event_number(currentBkgEventIndex);
  evt->add_vertex(pCopyOfGenVertex);
  HepMC::set_signal_process_vertex(evt,pCopyOfGenVertex);
  HepMC::set_signal_process_id(evt,spi);
  m_pOvrlMcEvColl->at(m_startingIndexForBackground+m_nBkgEventsReadSoFar) =  evt;
  updateClassificationMap(spi, currentBkgEventIndex, 0, RESTOFMB, true);
 
  unsigned int nCollisionVerticesFound(0);
  //loop over vertices in Background GenEvent
  ATH_MSG_VERBOSE( "Starting a vertex loop ... " );
  auto currentVertexIter = currentBackgroundEvent.vertices().begin();
  auto endOfCurrentListOfVertices = currentBackgroundEvent.vertices().end();
#else
  if ( HepMC::signal_process_vertex(&currentBackgroundEvent) ) pCopyOfGenVertex = new HepMC::GenVertex ( *currentBackgroundEvent.signal_process_vertex() );
  //insert the GenEvent into the overlay McEventCollection.
  m_pOvrlMcEvColl->at(m_startingIndexForBackground+m_nBkgEventsReadSoFar) = new HepMC::GenEvent(spi, currentBkgEventIndex, pCopyOfGenVertex );
  updateClassificationMap(spi, currentBkgEventIndex, 0, RESTOFMB, true);
 
  unsigned int nCollisionVerticesFound(0);
  //loop over vertices in Background GenEvent
  ATH_MSG_VERBOSE( "Starting a vertex loop ... " );
  auto currentVertexIter = currentBackgroundEvent.vertices_begin();
  auto endOfCurrentListOfVertices = currentBackgroundEvent.vertices_end();
#endif
  for (; currentVertexIter != endOfCurrentListOfVertices; ++currentVertexIter) {
    const auto&  pCurrentVertex=*currentVertexIter;
    HepMC::GenVertexPtr  pCopyOfVertexForClassification[NOPUTYPE];
    for (int type(INTIME); type<NOPUTYPE; ++type) pCopyOfVertexForClassification[type]=(HepMC::GenVertexPtr )nullptr;
 
    //check for collision vertices for in-time events
    bool isCollisionVertex(false);
    if(m_addBackgroundCollisionVertices && nCollisionVerticesFound<2 && currentEventTime==0.0) {
      isCollisionVertex=isInitialCollisionVertex(pCurrentVertex);
      if(isCollisionVertex) ++nCollisionVerticesFound;
    }
 
    //loop over outgoing particles in the current GenVertex keeping those not classified as NOPUTYPE
    ATH_MSG_VERBOSE( "Starting an outgoing particle loop ... " );
    for (const HepMC::ConstGenParticlePtr& currentVertexParticle: *pCurrentVertex){
      ATH_MSG_VERBOSE( "Found a particle at location " << std::hex << currentVertexParticle << std::dec  << " with PDG ID = " << currentVertexParticle->pdg_id() );
      HepMC::ConstGenVertexPtr  pCurrentParticleProductionVertex = currentVertexParticle->production_vertex();
      puType particleClassification(classifyVertex(currentVertexParticle, pCurrentParticleProductionVertex,currentEventTime));
      //hack to keep the complete vertex information for the interaction vertices of in-time background events
      if(isCollisionVertex && NOPUTYPE==particleClassification) {
        particleClassification=INTIME;
      }
      //add particle to appropriate vertex
      if (particleClassification<NOPUTYPE && m_saveType[particleClassification]) {
        if (!pCopyOfVertexForClassification[particleClassification]) {
          pCopyOfVertexForClassification[particleClassification] =HepMC::newGenVertexPtr(pCurrentVertex->position());
          ATH_MSG_VERBOSE( "Added bkg vertex " << pCopyOfVertexForClassification[particleClassification] << " at position " <<  pCopyOfVertexForClassification[particleClassification] << " for pu type = " << particleClassification );
        }
#ifdef HEPMC3
        pCopyOfVertexForClassification[particleClassification]->add_particle_out(std::make_shared<HepMC3::GenParticle>(currentVertexParticle->data()));
#else
        pCopyOfVertexForClassification[particleClassification]->add_particle_out( new HepMC::GenParticle(*currentVertexParticle) );
#endif
        ATH_MSG_VERBOSE( "Added bkg particle at location " << std::hex << currentVertexParticle << std::dec << " with PDG ID = " << currentVertexParticle->pdg_id() );
      }
    } //particle loop
    if (m_saveType[INTIME] && pCopyOfVertexForClassification[INTIME]) {
#ifdef HEPMC3
 for (const auto& currentVertexParticle:  pCurrentVertex->particles_in()) {
        pCopyOfVertexForClassification[INTIME]->add_particle_in (std::make_shared<HepMC3::GenParticle>(currentVertexParticle->data()));
      }
#else
      HepMC::GenVertex::particles_in_const_iterator currentVertexParticleIter(pCurrentVertex->particles_in_const_begin());
      const HepMC::GenVertex::particles_in_const_iterator endOfListOfParticlesFromCurrentVertex(pCurrentVertex->particles_in_const_end());
      for (; currentVertexParticleIter != endOfListOfParticlesFromCurrentVertex; ++currentVertexParticleIter) {
        pCopyOfVertexForClassification[INTIME]->add_particle_in ( new HepMC::GenParticle(**currentVertexParticleIter) );
      }
#endif
    }
    //keep vertices with outgoing particles
    for (int type(INTIME); type<NOPUTYPE; ++type) {
      if (!pCopyOfVertexForClassification[type]) continue;
      int n_particles_out=pCopyOfVertexForClassification[type]->particles_out_size();
      if (m_saveType[type] && (n_particles_out > 0) ) {
        updateClassificationMap(spi, currentBkgEventIndex, 0, type, false);
      }
    }
  } //vertex loop
 
  return StatusCode::SUCCESS;
}
 
bool MergeMcEventCollTool::isInitialCollisionVertex(const HepMC::ConstGenVertexPtr&  pCurrentVertex) const {
//AV: The olde version was too generator specific. 
#ifdef HEPMC3
  for (const auto& pCurrentVertexParticle: pCurrentVertex->particles_in()) {
#else
  auto currentVertexParticleIter = pCurrentVertex->particles_in_const_begin();
  auto  endOfListOfParticlesFromCurrentVertex = pCurrentVertex->particles_in_const_end();
  for( ;currentVertexParticleIter != endOfListOfParticlesFromCurrentVertex; ++currentVertexParticleIter ) {
    auto pCurrentVertexParticle = *currentVertexParticleIter;
#endif
    if (MC::isBeam(pCurrentVertexParticle)) return true;
  }
  return false;
}
 
MergeMcEventCollTool::puType MergeMcEventCollTool::classifyVertex(const HepMC::ConstGenParticlePtr&  pCurrentVertexParticle, const HepMC::ConstGenVertexPtr&  pCurrentParticleProductionVertex, double currentEventTime) {
  //=======================================================================
  //handle the slimming case
  //=======================================================================
  puType particleClassification(NOPUTYPE);
  if ( pCurrentParticleProductionVertex ) {
    //throw away unstable particles and particles outside eta cut
    if ( m_keepUnstable || MC::isSimStable(pCurrentVertexParticle) ) {
      if ( std::abs(pCurrentParticleProductionVertex->position().z()) < m_zRange ) {
        const float xi((pCurrentParticleProductionVertex->position()).x());
        const float yi((pCurrentParticleProductionVertex->position()).y());
        if ( !m_doSlimming || ( (xi*xi + yi*yi < m_r2Range) && (pCurrentVertexParticle->momentum().perp() > m_ptMin) ) ) {
          const double eta(pCurrentVertexParticle->momentum().pseudoRapidity());
          if ( !m_doSlimming || (std::abs(eta) <= m_absEtaMax) ) {
            const bool currentEventIsInTime((m_lowTimeToKeep<=currentEventTime) && (currentEventTime<=m_highTimeToKeep));
            if ( currentEventIsInTime ) {
              // cout << "the Time is " << currentEventTime << std::endl;
              if ( 0.0==currentEventTime ) {
                particleClassification=INTIME;
              }
              else if (std::abs(eta) <= m_absEtaMax_outOfTime) {
                particleClassification=OUTOFTIME;
              }
              else {
                particleClassification=RESTOFMB;
              }
            }
            else {
              particleClassification=RESTOFMB;
            }
          } // r2 && eta cut
        } // ptmin cut
      } // zrange cut
      else {
        // select cavern events
        double mass(pCurrentVertexParticle->momentum().m());
        if ( mass < 0.0 ) { mass = 0.0; }
        const double kineticEnergy(pCurrentVertexParticle->momentum().e() - mass);
        if ( !m_doSlimming || ( (kineticEnergy > m_minKinE) && (MC::charge(pCurrentVertexParticle->pdg_id()) != 0) ) ) {
          particleClassification=CAVERN;
        }
      } // zrange cut
    } // keep unstable
  } // pCurrentParticleProductionVertex is not NULL
  return particleClassification;
}
 
StatusCode MergeMcEventCollTool::compressOutputMcEventCollection() {
  int currentClassification=int(INTIME);
  if (! m_pOvrlMcEvColl->empty()) {
    DataVector<HepMC::GenEvent>::iterator outputEventItr(m_pOvrlMcEvColl->begin());
    while(outputEventItr!=m_pOvrlMcEvColl->end()) { //as end may change
      const int signal_process_id(HepMC::signal_process_id((*outputEventItr))),event_number((*outputEventItr)->event_number());
      //Check for separators
      if(signal_process_id==0 && event_number==-1) {
        ++outputEventItr;
        ++currentClassification;
        continue;
      }
      if((*outputEventItr)->vertices_empty()) {
        //Delete empty GenEvent
        outputEventItr=m_pOvrlMcEvColl->erase(outputEventItr);
        ATH_MSG_VERBOSE( "compressOutputMcEventCollection() Removed Empty GenEvent #" << event_number << ", signal_process_id(" << signal_process_id << "), category = " << currentClassification);
        continue;
      }
      ++outputEventItr;
    }
  }
  return StatusCode::SUCCESS;
}
 
void MergeMcEventCollTool::updateClassificationMap(int signal_process_id, int event_number, int separator_hack, int classification, bool firstUpdateForThisEvent=false)
{
  if(m_newevent && !m_backgroundClassificationMap.empty()) {
    ATH_MSG_ERROR( "updateClassidificationMap: GenEvent #" << event_number << ", signal_process_id(" << signal_process_id << "), category = " << classification );
    ATH_MSG_ERROR ("Failed to clear background classification map! Size = "<< m_backgroundClassificationMap.size());
    m_backgroundClassificationMap.clear();
  }
  if(-1==classification && !m_newevent) {
    ATH_MSG_ERROR( "updateClassidificationMap: GenEvent #" << event_number << ", signal_process_id(" << signal_process_id << "), category = " << classification );
    ATH_MSG_FATAL ("Should only ever be one signal event in the background classification map! Bailing out.");
  }
  // Check for separators
  IndexKey key(makekey(signal_process_id,event_number));
  //Check for Separator GenEvents
  if(signal_process_id==0 && event_number==-1) {
    key=makekey(separator_hack,event_number);
  }
  ATH_MSG_VERBOSE( "updateClassidificationMap: GenEvent #" << event_number << ", signal_process_id(" << signal_process_id << "), category = " << classification << ", key = " << key);
  const PileUpBackgroundMap::iterator event(m_backgroundClassificationMap.find(key));
  if(event!=m_backgroundClassificationMap.end()) {
    if(firstUpdateForThisEvent) {
      ATH_MSG_ERROR( "updateClassidificationMap: Repeated KEY! "<< key <<". Previous category = " << event->second );
    }
    else {
      ATH_MSG_DEBUG( "updateClassidificationMap: Updating category for existing key "<< key <<". Previous category = " << event->second << ", new category = " << classification );
    }
    if(int(RESTOFMB)!=event->second) {
      if(event->second<=classification) return;
    }
  }
  m_backgroundClassificationMap[key]=classification;
  return;
}