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 // This file is part of the Acts project.
 //
 // Copyright (C) 2019-2023 CERN for the benefit of the Acts project
 //
 // This Source Code Form is subject to the terms of the Mozilla Public
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 #include "Acts/Vertexing/AdaptiveMultiVertexFitter.hpp"
 
 #include "Acts/Surfaces/PerigeeSurface.hpp"
 #include "Acts/Vertexing/KalmanVertexUpdater.hpp"
 #include "Acts/Vertexing/VertexingError.hpp"
 
 Acts::Result<void> Acts::AdaptiveMultiVertexFitter::fit(
     State& state, const VertexingOptions& vertexingOptions) const {
   // Reset annealing tool
   state.annealingState = AnnealingUtility::State();
 
   // Boolean indicating whether any of the vertices has moved more than
   // m_cfg.maxRelativeShift during the last iteration. We will keep iterating
   // until the equilibrium (i.e., the lowest temperature) is reached in
   // the annealing procedure and isSmallShift is true (or until the maximum
   // number of iterations is exceeded).
   bool isSmallShift = true;
 
   // Number of iterations counter
   unsigned int nIter = 0;
 
   // Start iterating
   while (nIter < m_cfg.maxIterations &&
          (!state.annealingState.equilibriumReached || !isSmallShift)) {
     // Initial loop over all vertices in state.vertexCollection
     for (auto vtx : state.vertexCollection) {
       VertexInfo& vtxInfo = state.vtxInfoMap[vtx];
       vtxInfo.relinearize = false;
       // Store old position of vertex, i.e. seed position
       // in case of first iteration or position determined
       // in previous iteration afterwards
       vtxInfo.oldPosition = vtx->fullPosition();
 
       // Calculate the x-y-distance between the current vertex position
       // and the linearization point of the tracks. If it is too large,
       // we relinearize the tracks and recalculate their 3D impact
       // parameters.
       ActsVector<2> xyDiff = vtxInfo.oldPosition.template head<2>() -
                              vtxInfo.linPoint.template head<2>();
       if (xyDiff.norm() > m_cfg.maxDistToLinPoint) {
         // Set flag for relinearization
         vtxInfo.relinearize = true;
         // Recalculate the track impact parameters at the current vertex
         // position
         auto prepareVertexResult =
             prepareVertexForFit(state, vtx, vertexingOptions);
         if (!prepareVertexResult.ok()) {
           // Print vertices and associated tracks if logger is in debug mode
           if (logger().doPrint(Logging::DEBUG)) {
             logDebugData(state, vertexingOptions.geoContext);
           }
           return prepareVertexResult.error();
         }
       }
 
       // Check if we use the constraint during the vertex fit
       if (state.vtxInfoMap[vtx].constraint.fullCovariance() !=
           SquareMatrix4::Zero()) {
         const Acts::Vertex& constraint = state.vtxInfoMap[vtx].constraint;
         vtx->setFullPosition(constraint.fullPosition());
         vtx->setFitQuality(constraint.fitQuality());
         vtx->setFullCovariance(constraint.fullCovariance());
       } else if (vtx->fullCovariance() == SquareMatrix4::Zero()) {
         return VertexingError::NoCovariance;
       }
 
       // Set vertexCompatibility for all TrackAtVertex objects
       // at the current vertex
       auto setCompatibilitiesResult =
           setAllVertexCompatibilities(state, vtx, vertexingOptions);
       if (!setCompatibilitiesResult.ok()) {
         // Print vertices and associated tracks if logger is in debug mode
         if (logger().doPrint(Logging::DEBUG)) {
           logDebugData(state, vertexingOptions.geoContext);
         }
         return setCompatibilitiesResult.error();
       }
     }  // End loop over vertex collection
 
     // Recalculate all track weights and update vertices
     auto setWeightsResult = setWeightsAndUpdate(state, vertexingOptions);
     if (!setWeightsResult.ok()) {
       // Print vertices and associated tracks if logger is in debug mode
       if (logger().doPrint(Logging::DEBUG)) {
         logDebugData(state, vertexingOptions.geoContext);
       }
       return setWeightsResult.error();
     }
 
     // Cool the system down, i.e., reduce the temperature parameter. At lower
     // temperatures, outlying tracks are downweighted more.
     if (!state.annealingState.equilibriumReached) {
       m_cfg.annealingTool.anneal(state.annealingState);
     }
 
     isSmallShift = checkSmallShift(state);
     ++nIter;
   }
   // Multivertex fit is finished
 
   // Check if smoothing is required
   if (m_cfg.doSmoothing) {
     doVertexSmoothing(state);
   }
 
   return {};
 }
 
 Acts::Result<void> Acts::AdaptiveMultiVertexFitter::addVtxToFit(
     State& state, Vertex& newVertex,
     const VertexingOptions& vertexingOptions) const {
   if (state.vtxInfoMap[&newVertex].trackLinks.empty()) {
     ACTS_ERROR(
         "newVertex does not have any associated tracks (i.e., its trackLinks "
         "are empty).")
     return VertexingError::EmptyInput;
   }
 
   std::vector<Vertex*> verticesToFit = {&newVertex};
 
   // List of vertices added in last iteration
   std::vector<Vertex*> lastIterAddedVertices = {&newVertex};
   // List of vertices added in current iteration
   std::vector<Vertex*> currentIterAddedVertices;
 
   // Fill verticesToFit with vertices that are connected to newVertex (via
   // tracks and/or other vertices).
   while (!lastIterAddedVertices.empty()) {
     for (auto& lastIterAddedVertex : lastIterAddedVertices) {
       // Loop over all tracks at lastIterAddedVertex
       const std::vector<InputTrack>& trks =
           state.vtxInfoMap[lastIterAddedVertex].trackLinks;
       for (const auto& trk : trks) {
         // Range of vertices that are associated with trk. The range is
         // represented via its bounds: begin refers to the first iterator of the
         // range; end refers to the iterator after the last iterator of the
         // range.
         auto [begin, end] = state.trackToVerticesMultiMap.equal_range(trk);
 
         for (auto it = begin; it != end; ++it) {
           // it->first corresponds to trk, it->second to one of its associated
           // vertices
           auto vtxToFit = it->second;
           // Add vertex to the fit if it is not already included
           if (!isAlreadyInList(vtxToFit, verticesToFit)) {
             verticesToFit.push_back(vtxToFit);
 
             // Collect vertices that were added this iteration
             if (vtxToFit != lastIterAddedVertex) {
               currentIterAddedVertices.push_back(vtxToFit);
             }
           }
         }  // End for loop over range of associated vertices
       }    // End loop over trackLinks
     }      // End loop over lastIterAddedVertices
 
     lastIterAddedVertices = currentIterAddedVertices;
     currentIterAddedVertices.clear();
   }  // End while loop
 
   state.vertexCollection = verticesToFit;
 
   // Save the 3D impact parameters of all tracks associated with newVertex.
   auto res = prepareVertexForFit(state, &newVertex, vertexingOptions);
   if (!res.ok()) {
     // Print vertices and associated tracks if logger is in debug mode
     if (logger().doPrint(Logging::DEBUG)) {
       logDebugData(state, vertexingOptions.geoContext);
     }
     return res.error();
   }
 
   // Perform fit on all added vertices
   auto fitRes = fit(state, vertexingOptions);
   if (!fitRes.ok()) {
     return fitRes.error();
   }
 
   return {};
 }
 
 bool Acts::AdaptiveMultiVertexFitter::isAlreadyInList(
     Vertex* vtx, const std::vector<Vertex*>& vertices) const {
   return std::find(vertices.begin(), vertices.end(), vtx) != vertices.end();
 }
 
 Acts::Result<void> Acts::AdaptiveMultiVertexFitter::prepareVertexForFit(
     State& state, Vertex* vtx, const VertexingOptions& vertexingOptions) const {
   // Vertex info object
   auto& vtxInfo = state.vtxInfoMap[vtx];
   // Vertex seed position
   const Vector3& seedPos = vtxInfo.seedPosition.template head<3>();
 
   // Loop over all tracks at the vertex
   for (const auto& trk : vtxInfo.trackLinks) {
     auto res = m_cfg.ipEst.estimate3DImpactParameters(
         vertexingOptions.geoContext, vertexingOptions.magFieldContext,
         m_cfg.extractParameters(trk), seedPos, state.ipState);
     if (!res.ok()) {
       return res.error();
     }
     // Save 3D impact parameters of the track
     vtxInfo.impactParams3D.emplace(trk, res.value());
   }
   return {};
 }
 
 Acts::Result<void> Acts::AdaptiveMultiVertexFitter::setAllVertexCompatibilities(
     State& state, Vertex* vtx, const VertexingOptions& vertexingOptions) const {
   VertexInfo& vtxInfo = state.vtxInfoMap[vtx];
 
   // Loop over all tracks that are associated with vtx and estimate their
   // compatibility
   for (const auto& trk : vtxInfo.trackLinks) {
     auto& trkAtVtx = state.tracksAtVerticesMap.at(std::make_pair(trk, vtx));
     // Recover from cases where linearization point != 0 but
     // more tracks were added later on
     if (vtxInfo.impactParams3D.find(trk) == vtxInfo.impactParams3D.end()) {
       auto res = m_cfg.ipEst.estimate3DImpactParameters(
           vertexingOptions.geoContext, vertexingOptions.magFieldContext,
           m_cfg.extractParameters(trk),
           VectorHelpers::position(vtxInfo.linPoint), state.ipState);
       if (!res.ok()) {
         return res.error();
       }
       // Set impactParams3D for current trackAtVertex
       vtxInfo.impactParams3D.emplace(trk, res.value());
     }
     // Set compatibility with current vertex
     Acts::Result<double> compatibilityResult(0.);
     if (m_cfg.useTime) {
       compatibilityResult = m_cfg.ipEst.getVertexCompatibility(
           vertexingOptions.geoContext, &(vtxInfo.impactParams3D.at(trk)),
           vtxInfo.oldPosition);
     } else {
       Acts::Vector3 vertexPosOnly =
           VectorHelpers::position(vtxInfo.oldPosition);
       compatibilityResult = m_cfg.ipEst.getVertexCompatibility(
           vertexingOptions.geoContext, &(vtxInfo.impactParams3D.at(trk)),
           vertexPosOnly);
     }
 
     if (!compatibilityResult.ok()) {
       return compatibilityResult.error();
     }
     trkAtVtx.vertexCompatibility = *compatibilityResult;
   }
   return {};
 }
 
 Acts::Result<void> Acts::AdaptiveMultiVertexFitter::setWeightsAndUpdate(
     State& state, const VertexingOptions& vertexingOptions) const {
   for (auto vtx : state.vertexCollection) {
     VertexInfo& vtxInfo = state.vtxInfoMap[vtx];
 
     if (vtxInfo.relinearize) {
       vtxInfo.linPoint = vtxInfo.oldPosition;
     }
 
     const std::shared_ptr<PerigeeSurface> vtxPerigeeSurface =
         Surface::makeShared<PerigeeSurface>(
             VectorHelpers::position(vtxInfo.linPoint));
 
     for (const auto& trk : vtxInfo.trackLinks) {
       auto& trkAtVtx = state.tracksAtVerticesMap.at(std::make_pair(trk, vtx));
 
       // Set trackWeight for current track
       trkAtVtx.trackWeight = m_cfg.annealingTool.getWeight(
           state.annealingState, trkAtVtx.vertexCompatibility,
           collectTrackToVertexCompatibilities(state, trk));
 
       if (trkAtVtx.trackWeight > m_cfg.minWeight) {
         // Check if track is already linearized and whether we need to
         // relinearize
         if (!trkAtVtx.isLinearized || vtxInfo.relinearize) {
           auto result = m_cfg.trackLinearizer(
               m_cfg.extractParameters(trk), vtxInfo.linPoint[3],
               *vtxPerigeeSurface, vertexingOptions.geoContext,
               vertexingOptions.magFieldContext, state.fieldCache);
           if (!result.ok()) {
             return result.error();
           }
 
           trkAtVtx.linearizedState = *result;
           trkAtVtx.isLinearized = true;
         }
         // Update the vertex with the new track. The second template
         // argument corresponds to the number of fitted vertex dimensions
         // (i.e., 3 if we only fit spatial coordinates and 4 if we also fit
         // time).
         KalmanVertexUpdater::updateVertexWithTrack(*vtx, trkAtVtx,
                                                    m_cfg.useTime ? 4 : 3);
       } else {
         ACTS_VERBOSE("Track weight too low. Skip track.");
       }
     }  // End loop over tracks at vertex
     ACTS_VERBOSE("New vertex position: " << vtx->fullPosition().transpose());
   }  // End loop over vertex collection
 
   return {};
 }
 
 std::vector<double>
 Acts::AdaptiveMultiVertexFitter::collectTrackToVertexCompatibilities(
     State& state, const InputTrack& trk) const {
   // Compatibilities of trk wrt all of its associated vertices
   std::vector<double> trkToVtxCompatibilities;
 
   // Range of vertices that are associated with trk. The range is
   // represented via its bounds: begin refers to the first iterator of the
   // range; end refers to the iterator after the last iterator of the range.
   auto [begin, end] = state.trackToVerticesMultiMap.equal_range(trk);
   // Allocate space in memory for the vector of compatibilities
   trkToVtxCompatibilities.reserve(std::distance(begin, end));
 
   for (auto it = begin; it != end; ++it) {
     // it->first corresponds to trk, it->second to one of its associated
     // vertices
     trkToVtxCompatibilities.push_back(
         state.tracksAtVerticesMap.at(std::make_pair(trk, it->second))
             .vertexCompatibility);
   }
 
   return trkToVtxCompatibilities;
 }
 
 bool Acts::AdaptiveMultiVertexFitter::checkSmallShift(State& state) const {
   for (auto* vtx : state.vertexCollection) {
     Vector3 diff =
         state.vtxInfoMap[vtx].oldPosition.template head<3>() - vtx->position();
     const SquareMatrix3& vtxCov = vtx->covariance();
     double relativeShift = diff.dot(vtxCov.inverse() * diff);
     if (relativeShift > m_cfg.maxRelativeShift) {
       return false;
     }
   }
   return true;
 }
 
 void Acts::AdaptiveMultiVertexFitter::doVertexSmoothing(State& state) const {
   for (const auto vtx : state.vertexCollection) {
     for (const auto& trk : state.vtxInfoMap[vtx].trackLinks) {
       auto& trkAtVtx = state.tracksAtVerticesMap.at(std::make_pair(trk, vtx));
       if (trkAtVtx.trackWeight > m_cfg.minWeight) {
         // Update the new track under the assumption that it originates at the
         // vertex. The second template argument corresponds to the number of
         // fitted vertex dimensions (i.e., 3 if we only fit spatial coordinates
         // and 4 if we also fit time).
         KalmanVertexUpdater::updateTrackWithVertex(trkAtVtx, *vtx,
                                                    m_cfg.useTime ? 4 : 3);
       }
     }
   }
 }
 
 void Acts::AdaptiveMultiVertexFitter::logDebugData(
     const State& state, const Acts::GeometryContext& geoContext) const {
   ACTS_DEBUG("Encountered an error when fitting the following "
              << state.vertexCollection.size() << " vertices:");
   for (std::size_t vtxInd = 0; vtxInd < state.vertexCollection.size();
        ++vtxInd) {
     auto vtx = state.vertexCollection[vtxInd];
     ACTS_DEBUG("Position of " << vtxInd << ". vertex seed:\n"
                               << state.vtxInfoMap.at(vtx).seedPosition);
     ACTS_DEBUG("Position of said vertex after the last fitting step:\n"
                << state.vtxInfoMap.at(vtx).oldPosition);
     ACTS_DEBUG("Associated tracks:");
     const auto& trks = state.vtxInfoMap.at(vtx).trackLinks;
     for (std::size_t trkInd = 0; trkInd < trks.size(); ++trkInd) {
       const auto& trkAtVtx =
           state.tracksAtVerticesMap.at(std::make_pair(trks[trkInd], vtx));
       const auto& trkParams = m_cfg.extractParameters(trkAtVtx.originalParams);
       ACTS_DEBUG(trkInd << ". track parameters:\n" << trkParams.parameters());
       ACTS_DEBUG(trkInd << ". track covariance matrix:\n"
                         << trkParams.covariance().value());
       ACTS_DEBUG("Origin of corresponding reference surface:\n"
                  << trkParams.referenceSurface().center(geoContext));
     }
   }
 }

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