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25 //
26 // G4HelixExplicitEuler implementation
27 //
28 // Helix Explicit Euler: x_1 = x_0 + helix(h)
29 // with helix(h) being a helix piece of length h.
30 // Most simple approach for solving linear differential equations.
31 // Take the current derivative and add it to the current position.
32 //
33 // Author: W.Wander <wwc@mit.edu>, 12.09.1997
34 // -------------------------------------------------------------------
35
36 #include "G4HelixExplicitEuler.hh"
37 #include "G4PhysicalConstants.hh"
38 #include "G4ThreeVector.hh"
39
40 G4HelixExplicitEuler::G4HelixExplicitEuler(G4Mag_EqRhs* EqRhs)
41 : G4MagHelicalStepper(EqRhs)
42 {
43 }
44
45 G4HelixExplicitEuler::~G4HelixExplicitEuler() = default;
46
47 void G4HelixExplicitEuler::Stepper( const G4double yInput[], // [7]
48 const G4double*,
49 G4double Step,
50 G4double yOut[], // [7]
51 G4double yErr[] )
52 {
53 // Estimation of the Stepping Angle
54 //
55 G4ThreeVector Bfld;
56 MagFieldEvaluate(yInput, Bfld);
57
58 const G4int nvar = 6 ;
59 G4double yTemp[8], yIn[8] ;
60 G4ThreeVector Bfld_midpoint;
61
62 // Saving yInput because yInput and yOut can be aliases for same array
63 //
64 for(G4int i=0; i<nvar; ++i)
65 {
66 yIn[i] = yInput[i];
67 }
68
69 G4double h = Step * 0.5;
70
71 // Do full step and two half steps
72 //
73 G4double yTemp2[7];
74 AdvanceHelix(yIn, Bfld, h, yTemp2,yTemp);
75 MagFieldEvaluate(yTemp2, Bfld_midpoint) ;
76 AdvanceHelix(yTemp2, Bfld_midpoint, h, yOut);
77 SetAngCurve(GetAngCurve() * 2);
78
79 // Error estimation
80 //
81 for(G4int i=0; i<nvar; ++i)
82 {
83 yErr[i] = yOut[i] - yTemp[i];
84 }
85 }
86
87 G4double G4HelixExplicitEuler::DistChord() const
88 {
89 // Implementation : must check whether h/R > 2 pi !!
90 // If( h/R < pi) use G4LineSection::DistLine
91 // Else DistChord=R_helix
92 //
93 G4double distChord;
94 G4double Ang_curve=GetAngCurve();
95
96
97 if(Ang_curve<=pi)
98 {
99 distChord=GetRadHelix()*(1-std::cos(0.5*Ang_curve));
100 }
101 else if(Ang_curve<twopi)
102 {
103 distChord=GetRadHelix()*(1+std::cos(0.5*(twopi-Ang_curve)));
104 }
105 else
106 {
107 distChord=2.*GetRadHelix();
108 }
109
110 return distChord;
111 }
112
113 void G4HelixExplicitEuler::DumbStepper( const G4double yIn[],
114 G4ThreeVector Bfld,
115 G4double h,
116 G4double yOut[] )
117 {
118 AdvanceHelix(yIn, Bfld, h, yOut);
119 }
120