CopyEventWeight.cxx

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/*
  Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
*/
 
#ifndef XAOD_ANALYSIS
 
#include "EvgenProdTools/CopyEventWeight.h"
#include "StoreGate/WriteDecorHandle.h"
#include "EventInfo/EventInfo.h"
#include "EventInfo/EventType.h"
 
CopyEventWeight::CopyEventWeight(const std::string& name, ISvcLocator* svcLoc)
  : GenBase(name, svcLoc)
{
}
 
StatusCode CopyEventWeight::initialize()
{
  ATH_CHECK(GenBase::initialize());
  ATH_CHECK(m_mcWeightsKey.initialize());
  return StatusCode::SUCCESS;
}
 
StatusCode CopyEventWeight::execute(const EventContext& ctx) {
  // Check that the collection isn't empty
  const size_t nEvents = events_const(ctx)->size();
  if (nEvents == 0) {
    ATH_MSG_WARNING("McEventCollection is empty");
    return StatusCode::SUCCESS;
  }
 
  // Get the event info/type object to be filled
  const EventInfo* pInputEvt(nullptr);
  CHECK(evtStore()->retrieve(pInputEvt));
  assert(pInputEvt);
  EventType* eventType = const_cast<EventType*>(pInputEvt->event_type());
 
  // Copy weights into EventInfo
  const size_t nw = event_const(ctx)->weights().size();
  if (nw == 0) ATH_MSG_WARNING("EVENT WEIGHT ARRAY EMPTY");
  std::vector<float> weights;
  for (size_t iw = 0; iw < nw; ++iw) {
    ATH_MSG_DEBUG("COPYING EVENT WEIGHT " << iw << "/" << nw << ": " << event_const(ctx)->weights()[iw]);
    eventType->set_mc_event_weight(event_const(ctx)->weights()[iw], iw, nw);
    weights.push_back(event_const(ctx)->weights()[iw]);
  }
 
  SG::WriteDecorHandle<xAOD::EventInfo,std::vector<float>> mcWeights(m_mcWeightsKey, ctx);
  mcWeights(0) = std::move(weights);
 
  // Post-hoc debug printouts
  ATH_MSG_DEBUG("Copied HepMC signal event weight(s) to EventInfo");
  if (nEvents > 1) ATH_MSG_DEBUG("Ignored event weights of " << nEvents-1 << "bkg events");
 
  return StatusCode::SUCCESS;
}
 
#endif