include/Geant4/G4BorisScheme.hh

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0024 //
0025 // G4BorisScheme
0026 //
0027 // Class description:
0028 //
0029 // Implementation of the Boris algorithm for advancing
0030 // charged particles in an electromagnetic field.
0031
0032 // Author: Divyansh Tiwari (CERN, Google Summer of Code 2022), 05.11.2022
0033 // Supervision: John Apostolakis (CERN), Renee Fatemi, Soon Yung Jun (FNAL)
0034 // --------------------------------------------------------------------
0035 #ifndef G4BORIS_SCHEME_HH
0036 #define G4BORIS_SCHEME_HH
0037
0038 #include "G4Types.hh"
0039
0040 #include <CLHEP/Units/PhysicalConstants.h>
0041
0042 class G4EquationOfMotion;
0043
0044 /**
0045  * @brief The G4BorisScheme class implements of the Boris algorithm for
0046  * advancing charged particles in an electromagnetic field.
0047  */
0048
0049 class G4BorisScheme
0050 {
0051   public:
0052
0053     /**
0054      * Default Constructor.
0055      */
0056     G4BorisScheme() = default;
0057
0058     /**
0059      * Constructor for the equation of motion.
0060      *  @param[in] equation Pointer to the equation of motion algorithm.
0061      *  @param[in] nvar The number of integration variables.
0062      */
0063     G4BorisScheme( G4EquationOfMotion* equation, G4int nvar = 6 );
0064
0065     /**
0066      * Default Destructor.
0067      */
0068     ~G4BorisScheme() = default;
0069
0070     /**
0071      * Does one step, updating velocity and position.
0072      *  @param[in] restMass Particle mass.
0073      *  @param[in] charge Particle charge.
0074      *  @param[in] yIn Initial position.
0075      *  @param[out] yOut Updated position.
0076      *  @param[in] hstep Proposed step.
0077      */
0078     void DoStep(G4double restMass, G4double charge, const G4double yIn[],
0079                 G4double yOut[], G4double hstep) const;
0080
0081     /**
0082      * Adopts the Boris Scheme Stepping to estimate the integration error.
0083      * Uses two half-steps (comparing to a full step) to obtain output and
0084      * error estimate.
0085      *  @param[in] yIn Initial position.
0086      *  @param[in] restMass Particle mass.
0087      *  @param[in] charge Particle charge.
0088      *  @param[in] hstep Proposed step.
0089      *  @param[out] yOut Updated position.
0090      *  @param[out] yErr The estimated error.
0091      */
0092     void StepWithErrorEstimate(const G4double yIn[], G4double restMass,
0093                                G4double charge, G4double hstep,
0094                                G4double yOut[], G4double yErr[]) const;
0095
0096     /**
0097      * Adopts the Boris Scheme Stepping to estimate the integration error.
0098      * Uses two half-steps (comparing to a full step) to obtain output and
0099      * error estimate. Same as above, but also returns the mid-point evaluation.
0100      *  @param[in] yIn Initial position.
0101      *  @param[in] restMass Particle mass.
0102      *  @param[in] charge Particle charge.
0103      *  @param[in] hstep Proposed step.
0104      *  @param[out] yMid tThe mid-point evaluation.
0105      *  @param[out] yOut Updated position.
0106      *  @param[out] yErr The estimated error.
0107      */
0108     void StepWithMidAndErrorEstimate(const G4double yIn[], G4double restMass,
0109                                      G4double charge, G4double hstep,
0110                     G4double yMid[], G4double yOut[], G4double yErr[]) const;
0111
0112     /**
0113      * Auxiliary methods returning a pointer to the equation of motion
0114      * and the number of integration variables.
0115      */
0116     inline G4EquationOfMotion* GetEquationOfMotion() const;
0117     inline G4int GetNumberOfVariables() const;
0118
0119   private:
0120
0121     /**
0122      * Internal methods for updating position and velocity, used in DoStep().
0123      */
0124     void UpdatePosition(const G4double restMass, const G4double charge,
0125                         const G4double yIn[], G4double yOut[], G4double hstep) const;
0126     void UpdateVelocity(const G4double restMass, const G4double charge,
0127                         const G4double yIn[], G4double yOut[], G4double hstep) const;
0128
0129     /**
0130      * Utility to mem-copy 'src' array data to 'dst'.
0131      */
0132     void copy(G4double dst[], const G4double src[]) const;
0133
0134   private:
0135
0136     G4EquationOfMotion* fEquation = nullptr;
0137     G4int fnvar = 8;
0138     static constexpr G4double c_l = CLHEP::c_light/CLHEP::m*CLHEP::second;
0139 };
0140
0141 #include "G4BorisScheme.icc"
0142
0143 #endif