TrackTruthLookup.cxx

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/*
  Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
*/
 
#include "TrackTruthLookup.h"
#include "AthContainers/ConstAccessor.h"
 
namespace IDPVM {
// Utility function to get the linked truth particle from a track.
// Taken directly from InDetPhysValLargeD0Tool.cxx
  const xAOD::TruthParticle*
  getTruthPointer(const xAOD::TrackParticle& track) {
    using ElementTruthLink_t = ElementLink<xAOD::TruthParticleContainer>;
    const xAOD::TruthParticle* result(nullptr);
 
    // Check whether truthParticleLink exists.
    static const SG::ConstAccessor<ElementTruthLink_t> truthParticleLinkAcc("truthParticleLink");
    if (truthParticleLinkAcc.isAvailable(track)) {
      // If so, get linked xAOD::TruthParticle.
      const ElementTruthLink_t ptruthContainer =
        truthParticleLinkAcc(track);
      if (ptruthContainer.isValid()) {
        result = *ptruthContainer;
      }
    }
    return result;
  }
 
  std::vector<const xAOD::TrackParticle*>
  TrackTruthLookup::getTracks(const xAOD::TruthParticle* truth) const {
    // C++ try-catch blocks are zero-cost if no exception is thrown, so
    // performance should be unaffected by this check.
    try {
      return m_mapTruth.at(truth);
    } catch (const std::out_of_range& oor) {
      throw std::out_of_range(
              "Truth particle was not found in lookup map. Did you remember to call TrackTruthLookup::cache?");
    }
  }
 
  const xAOD::TruthParticle*
  TrackTruthLookup::getTruth(const xAOD::TrackParticle* track) const {
    // C++ try-catch blocks are zero-cost if no exception is thrown, so
    // performance should be unaffected by this check.
    try {
      return m_mapTrack.at(track);
    } catch (const std::out_of_range& oor) {
      throw std::out_of_range(
              "Track particle was not found in lookup map. Did you remember to call TrackTruthLookup::cache?");
    }
  }
 
  void
  TrackTruthLookup::cacheTracks(const xAOD::TrackParticleContainer* trackParticles) {
    // Cache all track particles.
    for (const xAOD::TrackParticle* track : *trackParticles) {
      const xAOD::TruthParticle* truth = getTruthPointer(*track);
 
      // Store pointer, even if null.
      m_mapTrack[track] = truth;
 
      // Store link in reverse direction as well, to avoid O(N^2) complexity.
      if (truth) {
        if (!contains(truth)) {
          // New truth particle; initialise vector.
          m_mapTruth[truth] = {
            track
          };
        } else {
          // Existing truth particle; append vector.
          m_mapTruth[truth].push_back(track);
        }
      }
    }
     }
 
  void
  TrackTruthLookup::cacheTruth(const xAOD::TruthParticleContainer* truthParticles) {
    // Cache remaining truth particles.
    for (const xAOD::TruthParticle* truth : *truthParticles) {
      if (!contains(truth)) {
        m_mapTruth[truth] = {};
      }
    }
     }
 
  void
  TrackTruthLookup::cacheTruth(const std::vector<const xAOD::TruthParticle*>* truthParticlesVec) {
    // Cache remaining truth particles.
    for (const xAOD::TruthParticle* truth : *truthParticlesVec) {
      if (!contains(truth)) {
        m_mapTruth[truth] = {};
      }
    }
     }
 
  void
  TrackTruthLookup::cache(const xAOD::TrackParticleContainer* trackParticles,
                          const xAOD::TruthParticleContainer* truthParticles) {
    // Clear existing cache.
    clear();
    cacheTracks(trackParticles);
    cacheTruth(truthParticles);
 }
 
  void
  TrackTruthLookup::cache(const xAOD::TrackParticleContainer* trackParticles,
                          const std::vector<const xAOD::TruthParticle*>* truthParticlesVec) {
    // Clear existing cache.
    clear();
    cacheTracks(trackParticles);
    cacheTruth(truthParticlesVec);
 }
} // namespace