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24 //
25 // Helper namespace field_utils implementation
26 //
27 // Author: Dmitry Sorokin, Google Summer of Code 2017
28 // Supervision: John Apostolakis, CERN
29 // --------------------------------------------------------------------
30
31 #include "G4FieldUtils.hh"
32
33 #include "G4SystemOfUnits.hh"
34 #include "G4PhysicalConstants.hh"
35
36 namespace field_utils {
37
38 G4double absoluteError(const G4double y[],
39 const G4double yError[],
40 G4double hstep)
41 {
42 const G4double momentum2 = getValue2(y, Value3D::Momentum);
43 const G4double invMomentum2 = 1.0 / momentum2;
44 const G4double positionError2 = getValue2(yError, Value3D::Position);
45 const G4double momentumError2 = getValue2(yError, Value3D::Momentum);
46 const G4double relativeMomentumError2 = momentumError2 * invMomentum2;
47
48 return std::max(std::sqrt(positionError2),
49 std::sqrt(relativeMomentumError2) * hstep);
50 }
51
52 G4double relativeError2(const G4double y[],
53 const G4double yerr[],
54 G4double h,
55 G4double eps_rel_max)
56 {
57 G4double errmax_sq;
58
59 G4double inv_eps_vel_sq = 1.0 / (eps_rel_max * eps_rel_max);
60 G4double errvel_sq = 0.0; // square of momentum vector difference
61
62 G4double eps_pos = eps_rel_max * h;
63 G4double inv_eps_pos_sq = 1.0 / (eps_pos * eps_pos);
64
65 // Evaluate accuracy
66 //
67 G4double errpos_sq = getValue2(yerr, Value3D::Position);
68 errpos_sq *= inv_eps_pos_sq; // Scale relative to required tolerance
69
70 // Accuracy for momentum
71 //
72 G4double magvel_sq = getValue2(y, Value3D::Momentum);
73 G4double sumerr_sq = getValue2(yerr, Value3D::Momentum);
74 if (magvel_sq > 0.0)
75 {
76 errvel_sq = sumerr_sq / magvel_sq;
77 }
78 else
79 {
80 G4Exception("field_utils::relativeError","Field001",
81 JustWarning, "found case of zero momentum");
82 errvel_sq = sumerr_sq;
83 }
84 errvel_sq *= inv_eps_vel_sq;
85 errmax_sq = std::max(errpos_sq, errvel_sq);
86
87 return errmax_sq;
88 }
89
90 G4double relativeError(const G4double y[],
91 const G4double yError[],
92 const G4double h,
93 const G4double errorTolerance)
94 {
95 return std::sqrt(relativeError2(y, yError, h, errorTolerance));
96 }
97
98 void copy(G4double dst[], const G4double src[], std::size_t size)
99 {
100 std::memcpy(dst, src, sizeof(G4double) * size);
101 }
102
103
104 G4double inverseCurvatureRadius(G4double particleCharge,
105 G4double momentum,
106 G4double BField)
107 {
108 return -c_light * particleCharge * BField / momentum;
109 }
110
111 } // field_utils
112
113