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25 //
26 // G4BFieldIntegrationDriver implementation
27 //
28 // Specialized integration driver for pure magnetic field
29 //
30 // Author: D.Sorokin
31 // --------------------------------------------------------------------
32
33 #include "G4BFieldIntegrationDriver.hh"
34
35 #include "G4FieldTrack.hh"
36 #include "G4FieldUtils.hh"
37 #include "G4Exception.hh"
38 #include "G4PhysicalConstants.hh"
39 #include "G4SystemOfUnits.hh"
40 #include "templates.hh"
41
42
43 namespace {
44
45 G4Mag_EqRhs* toMagneticEquation(G4EquationOfMotion* equation)
46 {
47 auto e = dynamic_cast<G4Mag_EqRhs*>(equation);
48
49 if (e == nullptr)
50 {
51 G4Exception("G4BFieldIntegrationDriver::G4BFieldIntegrationDriver",
52 "GeomField0003", FatalErrorInArgument,
53 "Works only with G4Mag_EqRhs");
54 }
55
56 return e;
57 }
58
59 } // namespace
60
61
62 G4BFieldIntegrationDriver::G4BFieldIntegrationDriver(
63 std::unique_ptr<G4VIntegrationDriver> smallStepDriver,
64 std::unique_ptr<G4VIntegrationDriver> largeStepDriver)
65 : fSmallStepDriver(std::move(smallStepDriver)),
66 fLargeStepDriver(std::move(largeStepDriver)),
67 fCurrDriver(fSmallStepDriver.get()),
68 fEquation(toMagneticEquation(fCurrDriver->GetEquationOfMotion()))
69 {
70 if (fSmallStepDriver->GetEquationOfMotion()
71 != fLargeStepDriver->GetEquationOfMotion())
72 {
73 G4Exception("G4BFieldIntegrationDriver Constructor:",
74 "GeomField1001", FatalException, "different EoM");
75 }
76 }
77
78 G4double G4BFieldIntegrationDriver::AdvanceChordLimited(G4FieldTrack& yCurrent,
79 G4double stepMax,
80 G4double epsStep,
81 G4double chordDistance)
82 {
83 const G4double radius = CurvatureRadius(yCurrent);
84
85 G4VIntegrationDriver* driver = nullptr;
86 if (chordDistance < 2 * radius)
87 {
88 stepMax = std::min(stepMax, twopi * radius);
89 driver = fSmallStepDriver.get();
90 ++fSmallDriverSteps;
91 } else
92 {
93 driver = fLargeStepDriver.get();
94 ++fLargeDriverSteps;
95 }
96
97 if (driver != fCurrDriver)
98 {
99 driver->OnComputeStep();
100 }
101
102 fCurrDriver = driver;
103
104 return fCurrDriver->AdvanceChordLimited(yCurrent, stepMax,
105 epsStep, chordDistance);
106 }
107
108 void
109 G4BFieldIntegrationDriver::SetEquationOfMotion(G4EquationOfMotion* equation)
110 {
111 fEquation = toMagneticEquation(equation);
112 fSmallStepDriver->SetEquationOfMotion(equation);
113 fLargeStepDriver->SetEquationOfMotion(equation);
114 }
115
116 G4double
117 G4BFieldIntegrationDriver::CurvatureRadius(const G4FieldTrack& track) const
118 {
119 G4double field[G4Field::MAX_NUMBER_OF_COMPONENTS];
120
121 GetFieldValue(track, field);
122
123 const G4double Bmag2 = field[0] * field[0]
124 + field[1] * field[1]
125 + field[2] * field[2] ;
126 if (Bmag2 == 0.0 )
127 {
128 return DBL_MAX;
129 }
130
131 const G4double momentum2 = track.GetMomentum().mag2();
132 const G4double fCof_inv = eplus / std::abs(fEquation->FCof());
133
134 return std::sqrt(momentum2 / Bmag2) * fCof_inv;
135 }
136
137 void
138 G4BFieldIntegrationDriver::GetFieldValue(const G4FieldTrack& track,
139 G4double Field[] ) const
140 {
141 G4ThreeVector pos= track.GetPosition();
142 G4double positionTime[4]= { pos.x(), pos.y(), pos.z(),
143 track.GetLabTimeOfFlight() } ;
144
145 fEquation->GetFieldValue(positionTime, Field);
146 }
147
148 void G4BFieldIntegrationDriver::PrintStatistics() const
149 {
150 const auto totSteps = fSmallDriverSteps + fLargeDriverSteps;
151 const auto toFraction = [&](double value) { return value / totSteps * 100; };
152
153 G4cout << "============= G4BFieldIntegrationDriver statistics ===========\n"
154 << "total steps " << totSteps << " "
155 << "smallDriverSteps " << toFraction(fSmallDriverSteps) << " "
156 << "largeDriverSteps " << toFraction(fLargeDriverSteps) << "\n"
157 << "======================================\n";
158 }
159