EIC code displayed by LXR master/​acts/​Core/​include/​Acts/​Propagator/​StraightLineStepper.hpp	Source navigation Diff markup Identifier search General search
	Version: master test Revert   Change

File indexing completed on 2026-11-07 09:23:01

 // 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/Definitions/Algebra.hpp"
 #include "Acts/Definitions/Direction.hpp"
 #include "Acts/Definitions/TrackParametrization.hpp"
 #include "Acts/EventData/BoundTrackParameters.hpp"
 #include "Acts/EventData/detail/CorrectedTransformationFreeToBound.hpp"
 #include "Acts/MagneticField/NullBField.hpp"
 #include "Acts/Propagator/ConstrainedStep.hpp"
 #include "Acts/Propagator/NavigationTarget.hpp"
 #include "Acts/Propagator/PropagatorTraits.hpp"
 #include "Acts/Propagator/StepperOptions.hpp"
 #include "Acts/Propagator/StepperStatistics.hpp"
 #include "Acts/Propagator/detail/SteppingHelper.hpp"
 #include "Acts/Surfaces/BoundaryTolerance.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Utilities/Intersection.hpp"
 #include "Acts/Utilities/Logger.hpp"
 #include "Acts/Utilities/MathHelpers.hpp"
 #include "Acts/Utilities/Result.hpp"
 
 #include <cmath>
 #include <stdexcept>
 #include <string>
 #include <tuple>
 
 namespace Acts {
 
 class IVolumeMaterial;
 
 /// @brief straight line stepper based on Surface intersection
 ///
 /// The straight line stepper is a simple navigation stepper
 /// to be used to navigate through the tracking geometry. It can be
 /// used for simple material mapping, navigation validation
 class StraightLineStepper final {
  public:
   /// Type alias for bound track parameters
   using BoundParameters = BoundTrackParameters;
   /// Type alias for transport jacobian matrix
   using Jacobian = BoundMatrix;
   /// Type alias for covariance matrix
   using Covariance = BoundMatrix;
   /// Type alias for magnetic field (null field for straight line propagation)
   using BField = NullBField;
 
   struct Config {};
 
   /// Configuration options for straight line propagation.
   struct Options : public StepperPlainOptions {
     /// Constructor from geometry and magnetic field contexts
     /// @param gctx The geometry context
     /// @param mctx The magnetic field context
     Options(const GeometryContext& gctx, const MagneticFieldContext& mctx)
         : StepperPlainOptions(gctx, mctx) {}
 
     /// Set plain stepper options
     /// @param options The plain options to set
     void setPlainOptions(const StepperPlainOptions& options) {
       static_cast<StepperPlainOptions&>(*this) = options;
     }
   };
 
   /// State for track parameter propagation
   ///
   struct State {
     /// Constructor from the initial bound track parameters
     ///
     /// @param [in] optionsIn The options for the stepper
     ///
     /// @note the covariance matrix is copied when needed
     explicit State(const Options& optionsIn) : options(optionsIn) {}
 
     /// Configuration options for the stepper
     Options options;
 
     /// Jacobian from local to the global frame
     BoundToFreeMatrix jacToGlobal = BoundToFreeMatrix::Zero();
 
     /// Pure transport jacobian part from runge kutta integration
     FreeMatrix jacTransport = FreeMatrix::Identity();
 
     /// The propagation derivative
     FreeVector derivative = FreeVector::Zero();
 
     /// Internal free vector parameters
     FreeVector pars = FreeVector::Zero();
 
     /// Particle hypothesis
     ParticleHypothesis particleHypothesis = ParticleHypothesis::pion();
 
     /// Covariance matrix for track parameter uncertainties, set if the
     /// covariance is transported
     std::optional<Covariance> cov;
 
     /// accumulated path length state
     double pathAccumulated = 0.;
 
     /// Total number of performed steps
     std::size_t nSteps = 0;
 
     /// adaptive step size of the runge-kutta integration
     ConstrainedStep stepSize;
 
     /// Previous step size for overstep estimation (ignored for straight line
     /// stepper)
     double previousStepSize = 0.;
 
     /// Statistics of the stepper
     StepperStatistics statistics;
   };
 
   /// Create a stepper state from propagation options
   /// @param options The propagation options
   /// @return A new stepper state initialized with the provided options
   State makeState(const Options& options) const;
 
   /// Initialize the stepper state from bound track parameters
   /// @param state The stepper state to initialize
   /// @param par The bound track parameters to initialize from
   void initialize(State& state, const BoundParameters& par) const;
 
   /// Initialize the stepper state from bound parameters and components
   /// @param state The stepper state to initialize
   /// @param boundParams The bound parameter vector
   /// @param cov Optional covariance matrix
   /// @param particleHypothesis The particle hypothesis (mass, charge, etc.)
   /// @param surface The reference surface
   void initialize(State& state, const BoundVector& boundParams,
                   const std::optional<BoundMatrix>& cov,
                   ParticleHypothesis particleHypothesis,
                   const Surface& surface) const;
 
   /// Get the field for the stepping, this gives back a zero field
   /// @return Always returns zero magnetic field vector for straight-line propagation
   Result<Vector3> getField(State& /*state*/, const Vector3& /*pos*/) const {
     // get the field from the cell
     return Result<Vector3>::success({0., 0., 0.});
   }
 
   /// Current global geometric curvature d(direction)/ds in inverse length.
   /// Unchanged under propagation reversal; reflects current momentum and field.
   /// @param state Stepping state; the field cache may be updated
   /// @return Curvature vector, or a field lookup error
   Result<Vector3> curvature([[maybe_unused]] State& state) const {
     return Result<Vector3>::success(Vector3::Zero());
   }
 
   /// Global particle position accessor
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return Current global position vector
   Vector3 position(const State& state) const {
     return state.pars.template segment<3>(eFreePos0);
   }
 
   /// Momentum direction accessor
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return Current normalized direction vector
   Vector3 direction(const State& state) const {
     return state.pars.template segment<3>(eFreeDir0);
   }
 
   /// QoP direction accessor
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return Charge over momentum (q/p) value
   double qOverP(const State& state) const { return state.pars[eFreeQOverP]; }
 
   /// Absolute momentum accessor
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return Absolute momentum magnitude
   double absoluteMomentum(const State& state) const {
     return particleHypothesis(state).extractMomentum(qOverP(state));
   }
 
   /// Momentum accessor
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return Current momentum vector
   Vector3 momentum(const State& state) const {
     return absoluteMomentum(state) * direction(state);
   }
 
   /// Charge access
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return Electric charge of the particle
   double charge(const State& state) const {
     return particleHypothesis(state).extractCharge(qOverP(state));
   }
 
   /// Particle hypothesis
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return Reference to the particle hypothesis used
   const ParticleHypothesis& particleHypothesis(const State& state) const {
     return state.particleHypothesis;
   }
 
   /// Time access
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return The time coordinate from the free parameters vector
   double time(const State& state) const { return state.pars[eFreeTime]; }
 
   /// Update surface status
   ///
   /// This method intersects the provided surface and update the navigation
   /// step estimation accordingly (hence it changes the state). It also
   /// returns the status of the intersection to trigger onSurface in case
   /// the surface is reached.
   ///
   /// @param [in,out] state The stepping state (thread-local cache)
   /// @param [in] surface The surface provided
   /// @param [in] index The surface intersection index
   /// @param [in] navDir The navigation direction
   /// @param [in] boundaryTolerance The boundary check for this status update
   /// @param [in] surfaceTolerance Surface tolerance used for intersection
   /// @param [in] stype The step size type to be set
   /// @param [in] logger A logger instance
   /// @param curvature Global geometric curvature for the crossing estimate
   /// @return Status of the intersection indicating whether surface was reached
   IntersectionStatus updateSurfaceStatus(
       State& state, const Surface& surface, std::uint8_t index,
       Direction navDir, const BoundaryTolerance& boundaryTolerance,
       double surfaceTolerance, ConstrainedStep::Type stype,
       const Logger& logger = getDummyLogger(),
       const Vector3& curvature = Vector3::Zero()) const {
     return detail::updateSingleSurfaceStatus<StraightLineStepper>(
         *this, state, surface, index, navDir, boundaryTolerance,
         surfaceTolerance, stype, logger, curvature);
   }
 
   /// Update step size
   ///
   /// It checks the status to the reference surface & updates
   /// the step size accordingly
   ///
   /// @param state [in,out] The stepping state (thread-local cache)
   /// @param target [in] The NavigationTarget
   /// @param direction [in] The propagation direction
   /// @param stype [in] The step size type to be set
   void updateStepSize(State& state, const NavigationTarget& target,
                       Direction direction, ConstrainedStep::Type stype) const {
     static_cast<void>(direction);
     double stepSize = target.pathLength();
     updateStepSize(state, stepSize, stype);
   }
 
   /// Update step size - explicitly with a double
   ///
   /// @param state [in,out] The stepping state (thread-local cache)
   /// @param stepSize [in] The step size value
   /// @param stype [in] The step size type to be set
   void updateStepSize(State& state, double stepSize,
                       ConstrainedStep::Type stype) const {
     state.previousStepSize = state.stepSize.value();
     state.stepSize.update(stepSize, stype);
   }
 
   /// Get the step size
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @param stype [in] The step size type to be returned
   /// @return Current step size for the specified constraint type
   double getStepSize(const State& state, ConstrainedStep::Type stype) const {
     return state.stepSize.value(stype);
   }
 
   /// Release the Step size
   ///
   /// @param [in,out] state The stepping state (thread-local cache)
   /// @param [in] stype The step size type to be released
   void releaseStepSize(State& state, ConstrainedStep::Type stype) const {
     state.stepSize.release(stype);
   }
 
   /// Output the Step Size - single component
   ///
   /// @param state [in,out] The stepping state (thread-local cache)
   /// @return String representation of the current step size
   std::string outputStepSize(const State& state) const {
     return state.stepSize.toString();
   }
 
   /// Get the step size constraints
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return The step size constraints
   const ConstrainedStep& stepSize(const State& state) const {
     return state.stepSize;
   }
 
   /// Get the stepper statistics
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return The statistics since the last initialization
   const StepperStatistics& statistics(const State& state) const {
     return state.statistics;
   }
 
   /// Get the path length
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return The path length since the last initialization
   double pathLength(const State& state) const { return state.pathAccumulated; }
 
   /// Check if the state carries a covariance
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return True if the covariance is transported
   bool hasCovariance(const State& state) const { return state.cov.has_value(); }
 
   /// Get the covariance at the anchor
   ///
   /// The anchor is the frame of the last initialization, transport or update.
   ///
   /// @param state [in] The stepping state (thread-local cache)
   /// @return The covariance at the anchor, or no value if the state does not
   ///         carry a covariance
   const std::optional<Covariance>& covariance(const State& state) const {
     return state.cov;
   }
 
   /// Set the covariance at the anchor
   ///
   /// The state must already carry a covariance, because the stepper only
   /// transports the Jacobian while it has one.
   ///
   /// @param [in,out] state The stepping state (thread-local cache)
   /// @param [in] covariance The new covariance at the anchor
   /// @throws std::logic_error if the state does not carry a covariance
   void setCovariance(State& state, const Covariance& covariance) const {
     if (!state.cov.has_value()) {
       throw std::logic_error(
           "Cannot set the covariance of a state without a covariance");
     }
     state.cov = covariance;
   }
 
   /// Get the bound parameters at the current position
   ///
   /// The parameters carry the covariance at the anchor if the state has one.
   ///
   /// @note It does not check if the state is on @p surface or anchored on it
   ///
   /// @param [in] state The stepping state (thread-local cache)
   /// @param [in] surface The surface of the parameters
   /// @return The bound parameters, or a failure if the position cannot be
   ///         expressed on @p surface
   Result<BoundParameters> boundParameters(const State& state,
                                           const Surface& surface) const;
 
   /// @brief If necessary fill additional members needed for
   /// transportToCurvilinear
   ///
   /// Compute path length derivatives in case they have not been computed
   /// yet, which is the case if no step has been executed yet.
   ///
   /// @param [in, out] state The stepping state (thread-local cache)
   /// @return true if nothing is missing after this call, false otherwise.
   bool prepareCurvilinearState(State& state) const {
     // test whether the accumulated path has still its initial value.
     if (state.pathAccumulated != 0) {
       return true;
     }
 
     // dr/ds :
     state.derivative.template head<3>() = direction(state);
     // dt / ds
     state.derivative(eFreeTime) = fastHypot(
         1., state.particleHypothesis.mass() / absoluteMomentum(state));
     // d (dr/ds) / ds : == 0
     state.derivative.template segment<3>(4) = Acts::Vector3::Zero().transpose();
     // d qop / ds  == 0
     state.derivative(eFreeQOverP) = 0.;
 
     return true;
   }
 
   /// Get the curvilinear parameters at the current position
   ///
   /// The parameters carry the covariance at the anchor if the state has one.
   ///
   /// @param [in] state The stepping state (thread-local cache)
   /// @return The curvilinear parameters
   BoundParameters curvilinearParameters(const State& state) const;
 
   /// Method to update a stepper state to the some parameters
   ///
   /// This anchors the state on @p surface.
   ///
   /// @param [in,out] state State object that will be updated
   /// @param [in] freeParams Free parameters that will be written into @p state
   /// @param [in] boundParams Corresponding bound parameters used to update jacToGlobal in @p state
   /// @param [in] covariance Covariance that will be written into @p state if
   ///                        the state carries a covariance
   /// @param [in] surface The surface used to update the jacToGlobal
   void update(State& state, const FreeVector& freeParams,
               const BoundVector& boundParams, const Covariance& covariance,
               const Surface& surface) const;
 
   /// Method to update the stepper state
   ///
   /// @param [in,out] state State object that will be updated
   /// @param [in] uposition the updated position
   /// @param [in] udirection the updated direction
   /// @param [in] qop the updated qop value
   /// @param [in] time the updated time value
   void update(State& state, const Vector3& uposition, const Vector3& udirection,
               double qop, double time) const;
 
   /// Transport the covariance to the curvilinear frame at the current position
   ///
   /// This anchors the state on the curvilinear frame. Without a covariance
   /// the state does not change.
   ///
   /// @param [in,out] state State of the stepper
   /// @return The jacobian from the previous anchor to the curvilinear frame
   Jacobian transportToCurvilinear(State& state) const;
 
   /// Transport the covariance to a surface at the current position
   ///
   /// This anchors the state on @p surface. Without a covariance the state
   /// does not change. The state must be on @p surface, and it stays unchanged
   /// if it is not.
   ///
   /// @param [in,out] state State of the stepper
   /// @param [in] surface The surface to transport the covariance to
   /// @param [in] freeToBoundCorrection Correction for non-linearity effect during transform from free to bound
   /// @return The jacobian from the previous anchor to @p surface, or a failure
   ///         if the state is not on @p surface
   Result<Jacobian> transportToBound(
       State& state, const Surface& surface,
       const FreeToBoundCorrection& freeToBoundCorrection =
           FreeToBoundCorrection(false)) const;
 
   /// Perform a straight line propagation step
   ///
   /// @param [in,out] state State of the stepper
   /// @param propDir is the direction of propagation
   /// @param material is the optional volume material we are stepping through.
   //         This is simply ignored if `nullptr`.
   /// @return the result of the step
   ///
   /// @note The state contains the desired step size. It can be negative during
   ///       backwards track propagation.
   Result<double> step(State& state, Direction propDir,
                       const IVolumeMaterial* material) const {
     static_cast<void>(material);
 
     // use the adjusted step size
     const auto h = state.stepSize.value() * propDir;
     const auto m = state.particleHypothesis.mass();
     const auto p = absoluteMomentum(state);
     // time propagates along distance as 1/b = sqrt(1 + m²/p²)
     const auto dtds = fastHypot(1, m / p);
     // Update the track parameters according to the equations of motion
     Vector3 dir = direction(state);
     state.pars.template segment<3>(eFreePos0) += h * dir;
     state.pars[eFreeTime] += h * dtds;
 
     // Propagate the jacobian
     if (state.cov.has_value()) {
       // The step transport matrix in global coordinates
       FreeMatrix D = FreeMatrix::Identity();
       D.block<3, 3>(0, 4) = SquareMatrix<3>::Identity() * h;
       // Extend the calculation by the time propagation
       // d(t)/d(q/p) = h m^2 (q/p) / (q^2 dt/ds), with the q^2 folded into p
       // via p = |q| / |q/p|.
       D(3, 7) = h * m * m / (p * p * state.pars[eFreeQOverP] * dtds);
       // Set the derivative factor the time
       state.derivative(3) = dtds;
       // Update jacobian and derivative
       state.jacTransport = D * state.jacTransport;
       state.derivative.template head<3>() = dir;
     }
 
     // state the path length
     state.pathAccumulated += h;
     ++state.nSteps;
 
     ++state.statistics.nAttemptedSteps;
     ++state.statistics.nSuccessfulSteps;
     if (propDir != Direction::fromScalarZeroAsPositive(h)) {
       ++state.statistics.nReverseSteps;
     }
     state.statistics.pathLength += h;
     state.statistics.absolutePathLength += std::abs(h);
 
     return h;
   }
 };
 
 template <>
 struct SupportsBoundParameters<StraightLineStepper> : public std::true_type {};
 
 }  // namespace Acts

This page was automatically generated by the 2.3.7 LXR engine. The LXR team