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25 //
26 // G4ConstRK4
27 //
28 // class description:
29 //
30 // G4ConstRK4 performs the integration of one step with error calculation
31 // in constant magnetic field. The integration method is the same as in
32 // ClassicalRK4. The field value is assumed constant for the step.
33 // This field evaluation is called only once per step.
34 // G4ConstRK4 can be used only for magnetic fields.
35
36 // Created: J.Apostolakis, T.Nikitina - 18.09.2008
37 // -------------------------------------------------------------------
38 #ifndef G4CONSTRK4_HH
39 #define G4CONSTRK4_HH
40
41 #include "G4MagErrorStepper.hh"
42 #include "G4EquationOfMotion.hh"
43 #include "G4Mag_EqRhs.hh"
44
45 class G4ConstRK4 : public G4MagErrorStepper
46 {
47 public:
48
49 G4ConstRK4(G4Mag_EqRhs* EquationMotion, G4int numberOfStateVariables=8);
50 ~G4ConstRK4() override;
51
52 G4ConstRK4(const G4ConstRK4&) = delete;
53 G4ConstRK4& operator=(const G4ConstRK4&) = delete;
54 // Copy constructor and assignment operator not allowed
55
56 void Stepper( const G4double y[],
57 const G4double dydx[],
58 G4double h,
59 G4double yout[],
60 G4double yerr[] ) override;
61 void DumbStepper( const G4double yIn[],
62 const G4double dydx[],
63 G4double h,
64 G4double yOut[] ) override ;
65 G4double DistChord() const override;
66
67 inline void RightHandSideConst(const G4double y[],
68 G4double dydx[] ) const;
69
70 inline void GetConstField(const G4double y[], G4double Field[]);
71
72 G4int IntegratorOrder() const override { return 4; }
73
74 private:
75
76 G4ThreeVector fInitialPoint, fMidPoint, fFinalPoint;
77 // Data stored in order to find the chord
78 G4double *dydxm, *dydxt, *yt; // scratch space - not state
79 G4double *yInitial, *yMiddle, *dydxMid, *yOneStep;
80 G4Mag_EqRhs* fEq = nullptr;
81 G4double Field[3];
82 };
83
84 // Inline methods
85
86 inline void G4ConstRK4::RightHandSideConst(const G4double y[],
87 G4double dydx[] ) const
88 {
89
90 G4double momentum_mag_square = y[3]*y[3] + y[4]*y[4] + y[5]*y[5];
91 G4double inv_momentum_magnitude = 1.0 / std::sqrt( momentum_mag_square );
92
93 G4double cof = fEq->FCof()*inv_momentum_magnitude;
94
95 dydx[0] = y[3]*inv_momentum_magnitude; // (d/ds)x = Vx/V
96 dydx[1] = y[4]*inv_momentum_magnitude; // (d/ds)y = Vy/V
97 dydx[2] = y[5]*inv_momentum_magnitude; // (d/ds)z = Vz/V
98
99 dydx[3] = cof*(y[4]*Field[2] - y[5]*Field[1]) ; // Ax = a*(Vy*Bz - Vz*By)
100 dydx[4] = cof*(y[5]*Field[0] - y[3]*Field[2]) ; // Ay = a*(Vz*Bx - Vx*Bz)
101 dydx[5] = cof*(y[3]*Field[1] - y[4]*Field[0]) ; // Az = a*(Vx*By - Vy*Bx)
102 }
103
104 inline void G4ConstRK4::GetConstField(const G4double y[], G4double B[])
105 {
106 G4double PositionAndTime[4];
107
108 PositionAndTime[0] = y[0];
109 PositionAndTime[1] = y[1];
110 PositionAndTime[2] = y[2];
111 // Global Time
112 PositionAndTime[3] = y[7];
113 fEq -> GetFieldValue(PositionAndTime, B);
114 }
115
116 #endif
117