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 // This file is part of the Acts project.
 //
 // Copyright (C) 2016-2020 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/.
 
 #pragma once
 
 #include "Acts/Definitions/Tolerance.hpp"
 #include "Acts/EventData/detail/PrintParameters.hpp"
 #include "Acts/EventData/detail/TransformationFreeToBound.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Utilities/UnitVectors.hpp"
 #include "Acts/Utilities/detail/periodic.hpp"
 
 #include <cassert>
 #include <cmath>
 #include <memory>
 #include <type_traits>
 
 namespace Acts {
 
 /// Track parameters bound to a reference surface for a single track.
 ///
 /// @tparam particle_hypothesis_t Helper type to interpret the particle charge/momentum
 ///
 /// This is intended as a user-facing data class that adds additional accessors
 /// and charge/momentum interpretation on top of the pure parameters vector. All
 /// parameters and their corresponding covariance matrix are stored in bound
 /// parametrization. The specific definition of the local spatial parameters is
 /// defined by the associated surface.
 ///
 /// @note This class holds shared ownership on its reference surface.
 template <class particle_hypothesis_t>
 class GenericBoundTrackParameters {
  public:
   using Scalar = ActsScalar;
   using ParametersVector = BoundVector;
   using CovarianceMatrix = BoundSquareMatrix;
   using ParticleHypothesis = particle_hypothesis_t;
 
   /// Construct from a parameters vector on the surface and particle charge.
   ///
   /// @param surface Reference surface the parameters are defined on
   /// @param params Bound parameters vector
   /// @param cov Bound parameters covariance matrix
   /// @param particleHypothesis Particle hypothesis
   ///
   /// In principle, only the charge magnitude is needed her to allow unambiguous
   /// extraction of the absolute momentum. The particle charge is required as
   /// an input here to be consistent with the other constructors below that
   /// that also take the charge as an input. The charge sign is only used in
   /// debug builds to check for consistency with the q/p parameter.
   GenericBoundTrackParameters(std::shared_ptr<const Surface> surface,
                               const ParametersVector& params,
                               std::optional<CovarianceMatrix> cov,
                               ParticleHypothesis particleHypothesis)
       : m_params(params),
         m_cov(std::move(cov)),
         m_surface(std::move(surface)),
         m_particleHypothesis(std::move(particleHypothesis)) {
     assert(m_surface);
     normalizePhiTheta();
   }
 
   /// Converts a bound track parameter with a different hypothesis.
   template <typename other_particle_hypothesis_t>
   GenericBoundTrackParameters(
       const GenericBoundTrackParameters<other_particle_hypothesis_t>& other)
       : GenericBoundTrackParameters(other.referenceSurface().getSharedPtr(),
                                     other.parameters(), other.covariance(),
                                     other.particleHypothesis()) {}
 
   /// Factory to construct from four-position, direction, absolute momentum, and
   /// charge.
   ///
   /// @param surface Reference surface the parameters are defined on
   /// @param geoCtx Geometry context for the local-to-global transformation
   /// @param pos4 Track position/time four-vector
   /// @param dir Track direction three-vector; normalization is ignored
   /// @param qOverP Charge over momentum
   /// @param cov Bound parameters covariance matrix
   /// @param particleHypothesis Particle hypothesis
   /// @param tolerance Tolerance used for globalToLocal
   ///
   /// @note The returned result indicates whether the free parameters could
   /// successfully be converted to on-surface parameters.
   static Result<GenericBoundTrackParameters> create(
       std::shared_ptr<const Surface> surface, const GeometryContext& geoCtx,
       const Vector4& pos4, const Vector3& dir, Scalar qOverP,
       std::optional<CovarianceMatrix> cov,
       ParticleHypothesis particleHypothesis,
       ActsScalar tolerance = s_onSurfaceTolerance) {
     Result<BoundVector> bound = detail::transformFreeToBoundParameters(
         pos4.segment<3>(ePos0), pos4[eTime], dir, qOverP, *surface, geoCtx,
         tolerance);
 
     if (!bound.ok()) {
       return bound.error();
     }
 
     return GenericBoundTrackParameters{std::move(surface), std::move(*bound),
                                        std::move(cov),
                                        std::move(particleHypothesis)};
   }
 
   /// Parameters are not default constructible due to the charge type.
   GenericBoundTrackParameters() = delete;
   GenericBoundTrackParameters(const GenericBoundTrackParameters&) = default;
   GenericBoundTrackParameters(GenericBoundTrackParameters&&) = default;
   ~GenericBoundTrackParameters() = default;
   GenericBoundTrackParameters& operator=(const GenericBoundTrackParameters&) =
       default;
   GenericBoundTrackParameters& operator=(GenericBoundTrackParameters&&) =
       default;
 
   /// Parameters vector.
   ParametersVector& parameters() { return m_params; }
   /// Parameters vector.
   const ParametersVector& parameters() const { return m_params; }
   /// Vector of spatial impact parameters (i.e., d0 and z0)
   ActsVector<2> spatialImpactParameters() const { return m_params.head<2>(); }
   /// Vector of spatial and temporal impact parameters (i.e., d0, z0, and t)
   ActsVector<3> impactParameters() const {
     ActsVector<3> ip;
     ip.template head<2>() = m_params.template head<2>();
     ip(2) = m_params(eBoundTime);
     return ip;
   }
 
   /// Optional covariance matrix.
   std::optional<CovarianceMatrix>& covariance() { return m_cov; }
   /// Optional covariance matrix.
   const std::optional<CovarianceMatrix>& covariance() const { return m_cov; }
   /// Covariance matrix of the spatial impact parameters (i.e., of d0 and z0)
   std::optional<ActsSquareMatrix<2>> spatialImpactParameterCovariance() const {
     if (!m_cov.has_value()) {
       return std::nullopt;
     }
 
     return m_cov.value().template topLeftCorner<2, 2>();
   }
 
   /// Covariance matrix of the spatial and temporal impact parameters (i.e., of
   /// d0, z0, and t)
   std::optional<ActsSquareMatrix<3>> impactParameterCovariance() const {
     if (!m_cov.has_value()) {
       return std::nullopt;
     }
 
     ActsSquareMatrix<3> ipCov;
     ipCov.template topLeftCorner<2, 2>() =
         m_cov.value().template topLeftCorner<2, 2>();
     ipCov.template block<2, 1>(0, 2) =
         m_cov.value().template block<2, 1>(0, eBoundTime);
     ipCov.template block<1, 2>(2, 0) =
         m_cov.value().template block<1, 2>(eBoundTime, 0);
     ipCov(2, 2) = m_cov.value()(eBoundTime, eBoundTime);
     return ipCov;
   }
 
   /// Access a single parameter value identified by its index.
   ///
   /// @tparam kIndex Track parameter index
   template <BoundIndices kIndex>
   Scalar get() const {
     return m_params[kIndex];
   }
 
   /// Local spatial position two-vector.
   Vector2 localPosition() const { return m_params.segment<2>(eBoundLoc0); }
   /// Space-time position four-vector.
   ///
   /// @param[in] geoCtx Geometry context for the local-to-global
   /// transformation
   ///
   /// This uses the associated surface to transform the local position on
   /// the surface to globalcoordinates. This requires a geometry context to
   /// select the appropriate transformation and might be a computationally
   /// expensive operation.
   Vector4 fourPosition(const GeometryContext& geoCtx) const {
     Vector4 pos4;
     pos4.segment<3>(ePos0) =
         m_surface->localToGlobal(geoCtx, localPosition(), direction());
     pos4[eTime] = m_params[eBoundTime];
     return pos4;
   }
   /// Spatial position three-vector.
   ///
   /// @param[in] geoCtx Geometry context for the local-to-global
   /// transformation
   ///
   /// This uses the associated surface to transform the local position on
   /// the surface to globalcoordinates. This requires a geometry context to
   /// select the appropriate transformation and might be a computationally
   /// expensive operation.
   Vector3 position(const GeometryContext& geoCtx) const {
     return m_surface->localToGlobal(geoCtx, localPosition(), direction());
   }
   /// Time coordinate.
   Scalar time() const { return m_params[eBoundTime]; }
 
   /// Phi direction.
   Scalar phi() const { return m_params[eBoundPhi]; }
   /// Theta direction.
   Scalar theta() const { return m_params[eBoundTheta]; }
   /// Charge over momentum.
   Scalar qOverP() const { return m_params[eBoundQOverP]; }
 
   /// Unit direction three-vector, i.e. the normalized momentum
   /// three-vector.
   Vector3 direction() const {
     return makeDirectionFromPhiTheta(m_params[eBoundPhi],
                                      m_params[eBoundTheta]);
   }
   /// Absolute momentum.
   Scalar absoluteMomentum() const {
     return m_particleHypothesis.extractMomentum(m_params[eBoundQOverP]);
   }
   /// Transverse momentum.
   Scalar transverseMomentum() const {
     return std::sin(m_params[eBoundTheta]) * absoluteMomentum();
   }
   /// Momentum three-vector.
   Vector3 momentum() const { return absoluteMomentum() * direction(); }
 
   /// Particle electric charge.
   Scalar charge() const {
     return m_particleHypothesis.extractCharge(get<eBoundQOverP>());
   }
 
   /// Particle hypothesis.
   const ParticleHypothesis& particleHypothesis() const {
     return m_particleHypothesis;
   }
 
   /// Reference surface onto which the parameters are bound.
   const Surface& referenceSurface() const { return *m_surface; }
   /// Reference frame in which the local error is defined.
   ///
   /// @param[in] geoCtx Geometry context for the local-to-global
   /// transformation
   ///
   /// For planar surfaces, this is the transformation local-to-global
   /// rotation matrix. For non-planar surfaces, it is the local-to-global
   /// rotation matrix of the tangential plane at the track position.
   RotationMatrix3 referenceFrame(const GeometryContext& geoCtx) const {
     return m_surface->referenceFrame(geoCtx, position(geoCtx), momentum());
   }
 
  private:
   BoundVector m_params;
   std::optional<BoundSquareMatrix> m_cov;
   /// reference surface
   std::shared_ptr<const Surface> m_surface;
   // TODO use [[no_unique_address]] once we switch to C++20
   ParticleHypothesis m_particleHypothesis;
 
   /// Ensure phi and theta angles are within bounds.
   void normalizePhiTheta() {
     auto [phi, theta] =
         detail::normalizePhiTheta(m_params[eBoundPhi], m_params[eBoundTheta]);
     m_params[eBoundPhi] = phi;
     m_params[eBoundTheta] = theta;
   }
 
   /// Compare two bound track parameters for bitwise equality.
   ///
   /// @note Comparing track parameters for bitwise equality is not a good
   /// idea.
   ///   Depending on the context you might want to compare only the
   ///   parameter values, or compare them for compatibility instead of
   ///   equality; you might also have different (floating point) thresholds
   ///   of equality in different contexts. None of that can be handled by
   ///   this operator. Users should think really hard if this is what they
   ///   want and we might decided that we will remove this in the future.
   friend bool operator==(const GenericBoundTrackParameters& lhs,
                          const GenericBoundTrackParameters& rhs) {
     return (lhs.m_params == rhs.m_params) && (lhs.m_cov == rhs.m_cov) &&
            (lhs.m_surface == rhs.m_surface) &&
            (lhs.m_particleHypothesis == rhs.m_particleHypothesis);
   }
   /// Compare two bound track parameters for bitwise in-equality.
   friend bool operator!=(const GenericBoundTrackParameters& lhs,
                          const GenericBoundTrackParameters& rhs) {
     return !(lhs == rhs);
   }
   /// Print information to the output stream.
   friend std::ostream& operator<<(std::ostream& os,
                                   const GenericBoundTrackParameters& tp) {
     detail::printBoundParameters(
         os, tp.referenceSurface(), tp.parameters(),
         tp.covariance().has_value() ? &tp.covariance().value() : nullptr);
     return os;
   }
 };
 
 }  // namespace Acts

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