ElectronMaterialMixtureConvolution.cxx

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/*
  Copyright (C) 2020-2026 CERN for the benefit of the ATLAS collaboration
*/

 
#include "TrkGaussianSumFilter/ElectronMaterialMixtureConvolution.h"
#include "TrkGaussianSumFilterUtils/GsfConstants.h"
#include "TrkGaussianSumFilterUtils/KLGaussianMixtureReduction.h"
#include "TrkGaussianSumFilterUtils/MultiComponentStateAssembler.h"
#include "TrkGaussianSumFilterUtils/MultiComponentStateCombiner.h"
 
#include "TrkParameters/ComponentParameters.h"
#include "CxxUtils/inline_hints.h"
//
#include "TrkGeometry/Layer.h"
#include "TrkGeometry/MaterialProperties.h"
#include "TrkSurfaces/PerigeeSurface.h"
 
#include <array>
namespace {
 
ATH_FLATTEN
inline void
dummyCacheElement(GsfMaterial::Combined& elem)
{
  elem.numEntries = 1;
  elem.deltaPs[0] = 0;
  elem.parameters[0] = AmgVector(5)::Zero();
  elem.covariances[0] = AmgSymMatrix(5)::Zero();
}
 
// Avoid out-of-line Eigen calls
ATH_FLATTEN
inline void
updateCacheElement(GsfMaterial::Combined& updated,
                   size_t index,
                   const AmgVector(5) & parameters,
                   const AmgSymMatrix(5) * covariance)
{
  updated.parameters[index] = parameters;
  if (covariance) {
    updated.covariances[index] += *covariance;
  } else {
    updated.covariances[index].setZero();
  }
}
 
bool
updateP(double& qOverP, double deltaP)
{
  double p = 1. / std::abs(qOverP);
  p += deltaP;
  if (p <= 0.) {
    return false;
  }
  qOverP = qOverP > 0. ? 1. / p : -1. / p;
  return true;
}
 
std::pair<const Trk::MaterialProperties*, double>
getMaterialProperties(const Trk::TrackParameters* trackParameters,
                      const Trk::Layer& layer)
{
 
  const Trk::MaterialProperties* materialProperties(layer.fullUpdateMaterialProperties(*trackParameters));
  double pathCorrection(0.);
 
  // Bail out if still no material properties can be found
  if (!materialProperties) {
    return { nullptr, 0 };
  }
  // Define the path correction
  pathCorrection =
    pathCorrection > 0.
      ? pathCorrection
      : layer.surfaceRepresentation().pathCorrection(
          trackParameters->position(), trackParameters->momentum());
 
  // The pathlength ( in mm ) is the path correction * the thickness of the
  // material
  const double pathLength = pathCorrection * materialProperties->thickness();
  return { materialProperties, pathLength };
}
 
Trk::MultiComponentState createMergedState(const GSFUtils::MergeArray& merges,
                                           std::vector<GsfMaterial::Combined>& caches,
                                           const std::vector<std::pair<size_t, size_t>>& indices,
                                           const Trk::MultiComponentState& inputState){
 
  Trk::MultiComponentStateAssembler::Cache assemblerCache;
  size_t numComponents = indices.size();
  // Gather the merges we need
  std::vector<char> isMerged(numComponents, 0);
  // Merge components "From" to components "To"
  const int returnedMerges = merges.size();
  for (int i = 0; i < returnedMerges; ++i) {
    const int mini = merges[i].To;
    const int minj = merges[i].From;
    // Get the first TP
    const size_t stateIndex = indices[mini].first;
    const size_t materialIndex = indices[mini].second;
    // Copy weight and first parameters as they are needed later on
    // for updating the covariance
    const AmgVector(5) firstParameters =
        caches[stateIndex].parameters[materialIndex];
    const double firstWeight = caches[stateIndex].weights[materialIndex];
    // Get the second TP
    const size_t stateIndex2 = indices[minj].first;
    const size_t materialIndex2 = indices[minj].second;
    // Set as merged
    isMerged[minj] = 1;
    // Update first parameters and weight
    Trk::MultiComponentStateCombiner::combineParametersWithWeight(
        caches[stateIndex].parameters[materialIndex],
        caches[stateIndex].weights[materialIndex],
        caches[stateIndex2].parameters[materialIndex2],
        caches[stateIndex2].weights[materialIndex2]);
    // Update covariance
    Trk::MultiComponentStateCombiner::combineCovWithWeight(
        firstParameters, caches[stateIndex].covariances[materialIndex],
        firstWeight, caches[stateIndex2].parameters[materialIndex2],
        caches[stateIndex2].covariances[materialIndex2],
        caches[stateIndex2].weights[materialIndex2]);
    // Reset 2nd parameters values just for clarity
    caches[stateIndex2].parameters[materialIndex2].setZero();
    caches[stateIndex2].covariances[materialIndex2].setZero();
  }
 
  // Loop over remaining unmerged components
  for (size_t i(0); i < numComponents; ++i) {
    if (isMerged[i]) {
      continue;
    }
    // Build the TP
    const size_t stateIndex = indices[i].first;
    const size_t materialIndex = indices[i].second;
    AmgVector(5)& stateVector =
        caches[stateIndex].parameters[materialIndex];
    AmgSymMatrix(5)& measuredCov =
        caches[stateIndex].covariances[materialIndex];
 
    std::unique_ptr<Trk::TrackParameters> updatedTrackParameters =
        inputState[stateIndex]
            .params->associatedSurface()
            .createUniqueTrackParameters(
                stateVector[Trk::loc1], stateVector[Trk::loc2],
                stateVector[Trk::phi], stateVector[Trk::theta],
                stateVector[Trk::qOverP], measuredCov);
 
    const double updatedWeight = caches[stateIndex].weights[materialIndex];
 
    assemblerCache.multiComponentState.push_back(
        {std::move(updatedTrackParameters), updatedWeight});
    assemblerCache.validWeightSum += updatedWeight;
  }
  return Trk::MultiComponentStateAssembler::assembledState(
      std::move(assemblerCache));
}
} // end of anonymous namespace
 
Trk::ElectronMaterialMixtureConvolution::ElectronMaterialMixtureConvolution(
  const std::string& type,
  const std::string& name,
  const IInterface* parent)
  : AthAlgTool(type, name, parent)
{
  declareInterface<IMaterialMixtureConvolution>(this);
}
 
Trk::ElectronMaterialMixtureConvolution::~ElectronMaterialMixtureConvolution() = default;
 
StatusCode
Trk::ElectronMaterialMixtureConvolution::initialize()
{
  if (m_maximumNumberOfComponents > GSFConstants::maxNumberofStateComponents) {
    ATH_MSG_FATAL("Requested MaximumNumberOfComponents > "
                  << GSFConstants::maxNumberofStateComponents);
    return StatusCode::FAILURE;
  }
 
  m_materialEffects = std::make_unique<ElectronCombinedMaterialEffects>(
    m_parameterisationFileName, m_parameterisationFileNameHighX0);
  return StatusCode::SUCCESS;
}
 
/* ==========================================
   Update with full material effects
   ========================================== */
Trk::MultiComponentState
Trk::ElectronMaterialMixtureConvolution::update(
  std::vector<GsfMaterial::Combined>& caches,
  const Trk::MultiComponentState& multiComponentState,
  const Trk::Layer& layer,
  Trk::PropDirection direction) const
{
  const double updateFactor = 1.0;
  Trk::MultiComponentState updatedMergedState = update(
    caches, multiComponentState, layer, direction, updateFactor);
 
  if (updatedMergedState.empty()) {
    return {};
  }
  MultiComponentStateHelpers::renormaliseState(updatedMergedState);
  return updatedMergedState;
}
 
/* ==========================================
   Update with pre-update material effects
========================================== */
Trk::MultiComponentState
Trk::ElectronMaterialMixtureConvolution::preUpdate(
  std::vector<GsfMaterial::Combined>& caches,
  const Trk::MultiComponentState& multiComponentState,
  const Trk::Layer& layer,
  Trk::PropDirection direction) const
{
  const double updateFactor =
      layer.preUpdateMaterialFactor(*multiComponentState.front().params, direction);
 
  Trk::MultiComponentState updatedMergedState = update(caches,
                                                       multiComponentState,
                                                       layer,
                                                       direction,
                                                       updateFactor);
  if (updatedMergedState.empty()) {
    return {};
  }
  MultiComponentStateHelpers::renormaliseState(updatedMergedState);
  return updatedMergedState;
}
 
/* ==========================================
   Update with post-update material effects
   ========================================== */
Trk::MultiComponentState
Trk::ElectronMaterialMixtureConvolution::postUpdate(
  std::vector<GsfMaterial::Combined>& caches,
  const Trk::MultiComponentState& multiComponentState,
  const Trk::Layer& layer,
  Trk::PropDirection direction) const
{
  const double updateFactor = layer.postUpdateMaterialFactor(
      *multiComponentState.front().params, direction);
 
  Trk::MultiComponentState updatedMergedState =
      update(caches, multiComponentState, layer, direction, updateFactor);
 
  if (updatedMergedState.empty()) {
    return {};
  }
  MultiComponentStateHelpers::renormaliseState(updatedMergedState);
  return updatedMergedState;
}
 
Trk::MultiComponentState
Trk::ElectronMaterialMixtureConvolution::update(
  std::vector<GsfMaterial::Combined>& caches,
  const Trk::MultiComponentState& inputState,
  const Trk::Layer& layer,
  Trk::PropDirection direction,
  double updateFactor) const
{
 
  // Check the multi-component state is populated
  if (inputState.empty()) {
    return {};
  }
  if (updateFactor < 0.01) {
    // Bail out as factor is too small to bother about
    return {};
  }
  caches.resize(inputState.size());
 
  // Fill cache and work out how many final components there should be
  size_t numComponents(0);
  for (size_t i(0); i < inputState.size(); ++i) {
    const AmgSymMatrix(5)* measuredCov = inputState[i].params->covariance();
    // If the momentum is too dont apply material effects
    if (inputState[i].params->momentum().mag() <= 250. * Gaudi::Units::MeV) {
      dummyCacheElement(caches[i]);
      updateCacheElement(caches[i], 0, inputState[i].params->parameters(), measuredCov);
      caches[i].weights[0] = inputState[i].weight;
      numComponents += caches[i].numEntries;
      continue;
    }
    // Get the material effects and store them in the cache
    std::pair<const Trk::MaterialProperties*, double> matPropPair =
        getMaterialProperties(inputState[i].params.get(), layer);
 
    if (!matPropPair.first) {
      dummyCacheElement(caches[i]);
      updateCacheElement(caches[i], 0, inputState[i].params->parameters(), measuredCov);
      caches[i].weights[0] = inputState[i].weight;
      numComponents += caches[i].numEntries;
      continue;
    }
    // Now we can compute/apply actual material effects
    // Apply the update factor
    matPropPair.second *= updateFactor;
    m_materialEffects->compute(caches[i],
                              inputState[i],
                              *matPropPair.first,
                              matPropPair.second,
                              direction);
 
    // Apply material effects to input state and store results in cache
    // We have i material caches , one for each input state.
    // Each cache has j entries. They correspond to each
    // Gausian used to describe the Bethe Heitler.
    for (size_t j(0); j < caches[i].numEntries; ++j) {
      updateCacheElement(caches[i], j, inputState[i].params->parameters(), measuredCov);
      // Adjust q/p of the (delta) Parameters
      // make sure update is good.
      if (!updateP(caches[i].parameters[j][Trk::qOverP],
                   caches[i].deltaPs[j])) {
        ATH_MSG_ERROR("Cannot update state vector momentum!!!");
        return {};
      }
      // Store component weight
      caches[i].weights[j] *= inputState[i].weight;
      // Ensure weight of component is not too small to save us from potential
      // FPE's Value. Weights are double so the min of float should
      // be small enough and should be handled
      if (caches[i].weights[j] < std::numeric_limits<float>::min()) {
        caches[i].weights[j] = std::numeric_limits<float>::min();
      }
    }
    numComponents += caches[i].numEntries;
  } // End of loop filling the cache
 
  // Fill information for  calculating which components to merge
  // In addition scan all components for covariance matrices.
  // If one component is missing its error matrix,
  // component reduction is impossible.
  //
  bool componentWithoutMeasurement = false;
  // keep track of the state component and material effects indices
  // Effectively here we have M state X N Material effects
  // MXN components.
  std::vector<std::pair<size_t, size_t>> indices{};
  indices.resize(numComponents);
  GSFUtils::Component1DArray componentsArray(numComponents);
  size_t k(0);
  for (size_t i(0); i < inputState.size(); ++i) {
    for (size_t j(0); j < caches[i].numEntries; ++j) {
      const AmgSymMatrix(5)* measuredCov = inputState[i].params->covariance();
      // Fill in infomation
      const double cov =
          measuredCov ? caches[i].covariances[j](Trk::qOverP, Trk::qOverP)
                      : -1.;
      if (!measuredCov) {
        componentWithoutMeasurement = true;
      }
      componentsArray[k].mean = caches[i].parameters[j][Trk::qOverP];
      componentsArray[k].cov = cov;
      componentsArray[k].invCov = cov > 0 ? 1. / cov : 1e10;
      componentsArray[k].weight = caches[i].weights[j];
      indices[k] = {i, j};
      ++k;
    }
  }
 
  // fallback if we have a component without measurement
  if (componentWithoutMeasurement) {
    auto* result = std::max_element(
        componentsArray.begin(), componentsArray.end(),
        [](const auto& a, const auto& b) { return a.weight < b.weight; });
    auto index = std::distance(componentsArray.begin(), result);
    const size_t stateIndex = indices[index].first;
    const size_t materialIndex = indices[index].second;
 
    AmgVector(5)& updatedStateVector = caches[stateIndex].parameters[materialIndex];
    const AmgSymMatrix(5)* measuredCov = inputState[stateIndex].params->covariance();
    std::optional<AmgSymMatrix(5)> updatedCovariance = std::nullopt;
    if (measuredCov && caches[stateIndex].covariances.size() > materialIndex) {
      updatedCovariance =
          AmgSymMatrix(5)(caches[stateIndex].covariances[materialIndex]);
    }
    std::unique_ptr<Trk::TrackParameters> updatedTrackParameters =
        inputState[stateIndex]
            .params->associatedSurface()
            .createUniqueTrackParameters(
                updatedStateVector[Trk::loc1], updatedStateVector[Trk::loc2],
                updatedStateVector[Trk::phi], updatedStateVector[Trk::theta],
                updatedStateVector[Trk::qOverP], std::move(updatedCovariance));
 
    Trk::ComponentParameters dummyCompParams = {
        std::move(updatedTrackParameters), 1.};
    Trk::MultiComponentState returnMultiState;
    returnMultiState.push_back(std::move(dummyCompParams));
    return returnMultiState;
  }
 
  //Create the state to rerurn accounting for any needed merges.
  GSFUtils::MergeArray merges;
  if (numComponents > m_maximumNumberOfComponents) {
    merges = findMerges(std::move(componentsArray), m_maximumNumberOfComponents);
  }
  auto mergedState = createMergedState(merges, caches, indices, inputState);
 
  if (mergedState.size() > m_maximumNumberOfComponents) {
    ATH_MSG_ERROR("Merging failed, target size: " << m_maximumNumberOfComponents
                                                  << " final size: "
                                                  << mergedState.size());
  }
  return mergedState;
}