G4BorisScheme.hh

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// G4BorisScheme
//
// Class description:
//
// Implementation of the Boris algorithm for advancing 
// charged particles in an electromagnetic field.
 
// Author: Divyansh Tiwari, Google Summer of Code 2022
// Supervision: John Apostolakis,Renee Fatemi, Soon Yung Jun
// --------------------------------------------------------------------
#ifndef G4BORIS_SCHEME_HH
#define G4BORIS_SCHEME_HH
 
class G4EquationOfMotion;
 
#include "G4Types.hh"
 
 
// class G4EqMagElectricField;
 
// #include "G4FieldTrack.hh"
 
#include <CLHEP/Units/PhysicalConstants.h>
 
class G4BorisScheme
{
  public:
 
    G4BorisScheme() = default;
    G4BorisScheme( // G4EqMagElectricField
       G4EquationOfMotion* equation,
                        G4int nvar = 6);
   ~G4BorisScheme() = default;
 
    void DoStep( G4double restMass, G4double charge, const G4double yIn[], 
                 G4double yOut[], G4double hstep) const;
 
  protected:
    // Used to implement the 'DoStep' method above
    void UpdatePosition(const G4double restMass, const G4double charge, const G4double yIn[],
                 G4double yOut[], G4double hstep) const;
 
    void UpdateVelocity(const G4double restMass, const G4double charge, const G4double yIn[],
                 G4double yOut[], G4double hstep) const;
 
  public: 
    // - Methods using the Boris Scheme Stepping to estimate integration error
    void StepWithErrorEstimate(const G4double yIn[], G4double restMass, G4double charge, G4double hstep,
                               G4double yOut[], G4double yErr[]) const;
      // Use two half-steps (comparing to a full step) to obtain output and error estimate
 
   void StepWithMidAndErrorEstimate(const G4double yIn[], G4double restMass, G4double charge, G4double hstep,
                               G4double yMid[], G4double yOut[], G4double yErr[]) const;
      // Same, and also return mid-point evaluation
 
    // Auxiliary method
    inline G4EquationOfMotion* GetEquationOfMotion();
    // inline void SetEquationOfMotion(G4EquationOfMotion* equation);  // Un-needed, dangerous
 
    inline G4int GetNumberOfVariables() const;
   
  private:
 
    void copy(G4double dst[], const G4double src[]) const;
 
  private:
 
    G4EquationOfMotion* fEquation = nullptr;
    G4int fnvar = 8;
    static constexpr G4double c_l = CLHEP::c_light/CLHEP::m*CLHEP::second;
};
 
#include "G4BorisScheme.icc"
#endif