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 // This file is part of the ACTS project.
 //
 // Copyright (C) 2016 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 https://mozilla.org/MPL/2.0/.
 
 #pragma once
 
 #include "Acts/MagneticField/MagneticFieldProvider.hpp"
 #include "Acts/Utilities/AnnealingUtility.hpp"
 #include "Acts/Utilities/Logger.hpp"
 #include "Acts/Utilities/Result.hpp"
 #include "Acts/Vertexing/AMVFInfo.hpp"
 #include "Acts/Vertexing/ImpactPointEstimator.hpp"
 #include "Acts/Vertexing/TrackAtVertex.hpp"
 #include "Acts/Vertexing/TrackLinearizer.hpp"
 #include "Acts/Vertexing/Vertex.hpp"
 #include "Acts/Vertexing/VertexingError.hpp"
 #include "Acts/Vertexing/VertexingOptions.hpp"
 
 #include <algorithm>
 
 namespace Acts {
 
 /// @class AdaptiveMultiVertexFitter
 /// @brief Implements an adaptive multi-vertex fitter as described
 ///   in detail in Section 5.3.5 in:
 ///   Ref. (1): CERN-THESIS-2010-027, Author: Piacquadio, Giacinto:
 ///   `Identification of b-jets and investigation of the discovery potential
 ///   of a Higgs boson in the WH−−>lvbb¯ channel with the ATLAS experiment`
 ///
 class AdaptiveMultiVertexFitter {
  public:
   /// @brief The fitter state
   struct State {
     /// Constructor for multi-vertex fitter state
     /// @param field Magnetic field provider for track extrapolation
     /// @param magContext Magnetic field context for field evaluations
     State(const MagneticFieldProvider& field,
           const Acts::MagneticFieldContext& magContext)
         : ipState{field.makeCache(magContext)},
           fieldCache(field.makeCache(magContext)) {}
 
     /// Vertex collection to be fitted
     std::vector<Vertex*> vertexCollection;
 
     /// Annealing state for thermodynamic track weighting
     AnnealingUtility::State annealingState;
 
     /// Impact point estimator state for track parameter calculations
     ImpactPointEstimator::State ipState;
 
     /// Magnetic field cache for field evaluations during fitting
     MagneticFieldProvider::Cache fieldCache;
 
     /// Map storing vertex information for each vertex in the fit
     /// @todo Does this have to be a mutable pointer?
     std::map<Vertex*, VertexInfo> vtxInfoMap;
 
     /// Multimap connecting tracks to their associated vertices
     std::multimap<InputTrack, Vertex*> trackToVerticesMultiMap;
 
     /// Map storing track-at-vertex information for each track-vertex pair
     std::map<std::pair<InputTrack, Vertex*>, TrackAtVertex> tracksAtVerticesMap;
 
     /// Adds a vertex to trackToVerticesMultiMap
     /// @param vtx Vertex to add to the multimap with its associated tracks
     void addVertexToMultiMap(Vertex& vtx) {
       for (auto trk : vtxInfoMap[&vtx].trackLinks) {
         trackToVerticesMultiMap.emplace(trk, &vtx);
       }
     }
 
     /// Removes a vertex from trackToVerticesMultiMap
     /// @param vtx Vertex to remove from the multimap along with its track associations
     void removeVertexFromMultiMap(Vertex& vtx) {
       for (auto iter = trackToVerticesMultiMap.begin();
            iter != trackToVerticesMultiMap.end();) {
         if (iter->second == &vtx) {
           iter = trackToVerticesMultiMap.erase(iter);
         } else {
           ++iter;
         }
       }
     }
 
     /// Remove a vertex from the vertex collection
     /// @param vtxToRemove Vertex to remove from the collection
     /// @param logger Logger for diagnostic messages
     /// @return Result indicating success or failure of the removal operation
     Result<void> removeVertexFromCollection(Vertex& vtxToRemove,
                                             const Logger& logger) {
       auto it = std::ranges::find(vertexCollection, &vtxToRemove);
       // Check if the value was found before erasing
       if (it == vertexCollection.end()) {
         ACTS_ERROR("vtxToRemove is not part of vertexCollection.");
         return VertexingError::ElementNotFound;
       }
       // Erase the element if found
       vertexCollection.erase(it);
       return {};
     }
   };
 
   struct Config {
     /// @brief Config constructor
     ///
     /// @param est ImpactPointEstimator
     explicit Config(ImpactPointEstimator est) : ipEst(std::move(est)) {}
 
     // ImpactPointEstimator
     ImpactPointEstimator ipEst;
 
     /// Annealing tool used for a thermodynamic annealing scheme for the
     /// track weight factors in such a way that with high temperature values
     /// (at the beginning) only a slight preference is given to tracks
     /// compatible with the estimated vertex position. With lower temperatures
     /// the weighting get stricter such that all incompatible tracks will be
     /// dropped at the end while keeping all compatible tracks with a weight=1.
     ///   Ref. (1): CERN-THESIS-2010-027, Author: Piacquadio, Giacinto:
     ///   `Identification of b-jets and investigation of the discovery potential
     ///   of a Higgs boson in the WH−−>lvbb¯ channel with the ATLAS experiment`
     AnnealingUtility annealingTool;
 
     // Number of max iterations
     unsigned int maxIterations{30};
 
     // Max distance to linearization point allowed
     // without relinearization
     double maxDistToLinPoint{0.5};
 
     // Minimum track weight needed for track to be considered
     double minWeight{0.0001};
 
     // Max relative shift of vertex during one iteration
     double maxRelativeShift{0.01};
 
     // Do smoothing after multivertex fit
     bool doSmoothing{false};
 
     // Use time information when calculating the vertex compatibility
     bool useTime{false};
 
     // Function to extract parameters from InputTrack
     InputTrack::Extractor extractParameters;
 
     TrackLinearizer trackLinearizer;
   };
 
   /// @brief Constructor for user-defined InputTrack_t type !=
   /// BoundTrackParameters
   ///
   /// @param cfg Configuration object
   /// object
   /// @param logger The logging instance
   explicit AdaptiveMultiVertexFitter(
       Config cfg, std::unique_ptr<const Logger> logger = getDefaultLogger(
                       "AdaptiveMultiVertexFitter", Logging::INFO));
 
   /// @brief Adds a new vertex to an existing multi-vertex fit.
   /// 1. The 3D impact parameters are calculated for all tracks associated
   /// with newVertex.
   /// 2. A list of all vertices that are connected with newVertex via shared
   /// tracks is created. It also considers indirect connections (e.g., vertex A
   /// which shares a track with vertex B which, in turn, shares a track with
   /// newVertex).
   /// 3. The multivertex fit is performed for all vertices on said list.
   ///
   /// @param state Fitter state
   /// @param newVertices Vertex to be added to fit
   /// @param vertexingOptions Vertexing options
   ///
   /// @return Result<void> object
   Result<void> addVtxToFit(State& state,
                            const std::vector<Vertex*>& newVertices,
                            const VertexingOptions& vertexingOptions) const;
 
   /// @brief Performs a simultaneous fit of all vertices in
   /// state.vertexCollection
   ///
   /// @param state Fitter state
   /// @param vertexingOptions Vertexing options
   ///
   /// @return Result<void> object
   Result<void> fit(State& state,
                    const VertexingOptions& vertexingOptions) const;
 
  private:
   /// Configuration object
   const Config m_cfg;
 
   /// Logging instance
   std::unique_ptr<const Logger> m_logger;
 
   /// Private access to logging instance
   const Logger& logger() const { return *m_logger; }
 
   /// @brief Tests if vertex is already in list of vertices or not
   ///
   /// @param vtx Vertex to test
   /// @param verticesVec Vector of vertices to search
   ///
   /// @return True if vtx is already in verticesVec
   bool isAlreadyInList(Vertex* vtx,
                        const std::vector<Vertex*>& verticesVec) const;
 
   /// @brief 1) Calls ImpactPointEstimator::estimate3DImpactParameters
   /// for all tracks that are associated with vtx (i.e., all elements
   /// of the trackLinks vector in the VertexInfo of vtx).
   /// 2) Saves the 3D impact parameters in the VertexInfo of vtx.
   ///
   /// @param state Vertex fitter state
   /// @param vtx Vertex object
   /// @param vertexingOptions Vertexing options
   Result<void> prepareVertexForFit(
       State& state, Vertex* vtx,
       const VertexingOptions& vertexingOptions) const;
 
   /// @brief Sets the vertexCompatibility for all TrackAtVertex objects
   /// at the current vertex
   ///
   /// @param state Fitter state
   /// @param currentVtx Current vertex
   /// @param vertexingOptions Vertexing options
   Result<void> setAllVertexCompatibilities(
       State& state, Vertex* currentVtx,
       const VertexingOptions& vertexingOptions) const;
 
   /// @brief Sets weights to the track according to Eq.(5.46) in Ref.(1)
   ///  and updates the vertices by calling the VertexUpdater
   ///
   /// @param state Fitter state
   /// @param vertexingOptions Vertexing options
   Result<void> setWeightsAndUpdate(
       State& state, const VertexingOptions& vertexingOptions) const;
 
   /// @brief Collects the compatibility values of the track `trk`
   /// wrt to all of its associated vertices
   ///
   /// @param state Fitter state
   /// @param trk Track
   ///
   /// @return Vector of compatibility values
   std::vector<double> collectTrackToVertexCompatibilities(
       State& state, const InputTrack& trk) const;
 
   /// @brief Determines if any vertex position has shifted more than
   /// m_cfg.maxRelativeShift in the last iteration
   ///
   /// @param state Fitter state
   ///
   /// @return False if at least one shift was larger than maxRelativeShift
   bool checkSmallShift(State& state) const;
 
   /// @brief Updates tracks for current vertex with knowledge
   /// of current vertex position
   ///
   /// @param state Fitter state
   void doVertexSmoothing(State& state) const;
 
   /// @brief Logs vertices in state.vertexCollection and associated tracks
   ///
   /// @param state Fitter state
   /// @param geoContext Geometry context
   void logDebugData(const State& state,
                     const GeometryContext& geoContext) const;
 };
 
 }  // namespace Acts

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