include/Geant4/G4ConstRK4.hh

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0025 //
0026 // G4ConstRK4
0027 //
0028 // class description:
0029 //
0030 // G4ConstRK4 performs the integration of one step with error calculation
0031 // in constant magnetic field. The integration method is the same as in
0032 // ClassicalRK4. The field value is assumed constant for the step.
0033 // This field evaluation is called only once per step.
0034 // G4ConstRK4 can be used only for magnetic fields.
0035
0036 // Created: J.Apostolakis, T.Nikitina - 18.09.2008
0037 // -------------------------------------------------------------------
0038 #ifndef G4CONSTRK4_HH
0039 #define G4CONSTRK4_HH
0040
0041 #include "G4MagErrorStepper.hh"
0042 #include "G4EquationOfMotion.hh"
0043 #include "G4Mag_EqRhs.hh"
0044
0045 class G4ConstRK4 : public G4MagErrorStepper
0046 {
0047    public:
0048
0049      G4ConstRK4(G4Mag_EqRhs* EquationMotion, G4int numberOfStateVariables=8);
0050     ~G4ConstRK4() override;
0051
0052      G4ConstRK4(const G4ConstRK4&) = delete;
0053      G4ConstRK4& operator=(const G4ConstRK4&) = delete;
0054        // Copy constructor and assignment operator not allowed
0055
0056      void Stepper( const G4double y[],
0057                    const G4double dydx[],
0058                          G4double h,
0059                          G4double yout[],
0060                          G4double yerr[]  ) override;
0061      void DumbStepper( const G4double yIn[],
0062                        const G4double dydx[],
0063                              G4double h,
0064                              G4double yOut[] ) override ;
0065      G4double DistChord() const override;
0066
0067      inline void  RightHandSideConst(const G4double y[],
0068                                            G4double dydx[] ) const;
0069
0070      inline void  GetConstField(const G4double y[], G4double Field[]);
0071
0072      G4int IntegratorOrder() const override { return 4; }
0073
0074    private:
0075
0076      G4ThreeVector fInitialPoint, fMidPoint, fFinalPoint;
0077      // Data stored in order to find the chord
0078      G4double *dydxm, *dydxt, *yt; // scratch space - not state
0079      G4double *yInitial, *yMiddle, *dydxMid, *yOneStep;
0080      G4Mag_EqRhs* fEq = nullptr;
0081      G4double Field[3];
0082 };
0083
0084 // Inline methods
0085
0086 inline void G4ConstRK4::RightHandSideConst(const G4double y[],
0087                                                  G4double dydx[] ) const
0088 {
0089
0090   G4double momentum_mag_square = y[3]*y[3] + y[4]*y[4] + y[5]*y[5];
0091   G4double inv_momentum_magnitude = 1.0 / std::sqrt( momentum_mag_square );
0092
0093   G4double cof = fEq->FCof()*inv_momentum_magnitude;
0094
0095   dydx[0] = y[3]*inv_momentum_magnitude;       //  (d/ds)x = Vx/V
0096   dydx[1] = y[4]*inv_momentum_magnitude;       //  (d/ds)y = Vy/V
0097   dydx[2] = y[5]*inv_momentum_magnitude;       //  (d/ds)z = Vz/V
0098
0099   dydx[3] = cof*(y[4]*Field[2] - y[5]*Field[1]) ;   // Ax = a*(Vy*Bz - Vz*By)
0100   dydx[4] = cof*(y[5]*Field[0] - y[3]*Field[2]) ;   // Ay = a*(Vz*Bx - Vx*Bz)
0101   dydx[5] = cof*(y[3]*Field[1] - y[4]*Field[0]) ;   // Az = a*(Vx*By - Vy*Bx)
0102 }
0103
0104 inline void G4ConstRK4::GetConstField(const G4double y[], G4double B[])
0105 {
0106   G4double PositionAndTime[4];
0107
0108   PositionAndTime[0] = y[0];
0109   PositionAndTime[1] = y[1];
0110   PositionAndTime[2] = y[2];
0111   // Global Time
0112   PositionAndTime[3] = y[7];
0113   fEq -> GetFieldValue(PositionAndTime, B);
0114 }
0115
0116 #endif