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24 // 24 //
25 // G4ModifiedMidpoint implementation 25 // G4ModifiedMidpoint implementation
26 // 26 //
27 // Author: Dmitry Sorokin, Google Summer of Co 27 // Author: Dmitry Sorokin, Google Summer of Code 2016
28 // Supervision: John Apostolakis, CERN 28 // Supervision: John Apostolakis, CERN
29 // ------------------------------------------- 29 // --------------------------------------------------------------------
30 30
31 #include "G4ModifiedMidpoint.hh" 31 #include "G4ModifiedMidpoint.hh"
32 #include "G4FieldUtils.hh" 32 #include "G4FieldUtils.hh"
33 33
34 using namespace field_utils; 34 using namespace field_utils;
35 35
36 G4ModifiedMidpoint::G4ModifiedMidpoint( G4Equa 36 G4ModifiedMidpoint::G4ModifiedMidpoint( G4EquationOfMotion* equation,
37 G4int 37 G4int nvar, G4int steps )
38 : fEquation(equation), fnvar(nvar), fsteps(s 38 : fEquation(equation), fnvar(nvar), fsteps(steps)
39 { 39 {
40 if (nvar <= 0) 40 if (nvar <= 0)
41 { 41 {
42 G4Exception("G4ModifiedMidpoint::G4Modifie 42 G4Exception("G4ModifiedMidpoint::G4ModifiedMidpoint()",
43 "GeomField0002", FatalExceptio 43 "GeomField0002", FatalException,
44 "Invalid number of variables; 44 "Invalid number of variables; must be greater than zero!");
45 } 45 }
46 } 46 }
47 47
48 void G4ModifiedMidpoint::DoStep( const G4doubl 48 void G4ModifiedMidpoint::DoStep( const G4double yIn[], const G4double dydyIn[],
49 G4double yOut 49 G4double yOut[], G4double hstep) const
50 { 50 {
51 G4double y0[G4FieldTrack::ncompSVEC]; 51 G4double y0[G4FieldTrack::ncompSVEC];
52 G4double y1[G4FieldTrack::ncompSVEC]; 52 G4double y1[G4FieldTrack::ncompSVEC];
53 G4double yTemp[G4FieldTrack::ncompSVEC]; 53 G4double yTemp[G4FieldTrack::ncompSVEC];
54 setValue(yIn, Value1D::LabTime, y0, y1, yTem 54 setValue(yIn, Value1D::LabTime, y0, y1, yTemp, yOut);
55 55
56 G4double dydx[G4FieldTrack::ncompSVEC]; 56 G4double dydx[G4FieldTrack::ncompSVEC];
57 57
58 const G4double h = hstep / fsteps; 58 const G4double h = hstep / fsteps;
59 const G4double h2 = 2 * h; 59 const G4double h2 = 2 * h;
60 60
61 // y1 = yIn + h * dydx 61 // y1 = yIn + h * dydx
62 // 62 //
63 for (G4int i = 0; i < fnvar; ++i) 63 for (G4int i = 0; i < fnvar; ++i)
64 { 64 {
65 y1[i] = yIn[i] + h * dydyIn[i]; 65 y1[i] = yIn[i] + h * dydyIn[i];
66 } 66 }
67 67
68 fEquation->RightHandSide(y1, dydx); 68 fEquation->RightHandSide(y1, dydx);
69 69
70 copy(y0, yIn); 70 copy(y0, yIn);
71 71
72 // general step 72 // general step
73 // yTemp = y1; y1 = y0 + h2 * dydx; y0 = yTe 73 // yTemp = y1; y1 = y0 + h2 * dydx; y0 = yTemp
74 // 74 //
75 for (G4int i = 1; i < fsteps; ++i) 75 for (G4int i = 1; i < fsteps; ++i)
76 { 76 {
77 copy(yTemp, y1); 77 copy(yTemp, y1);
78 for (G4int j = 0; j < fnvar; ++j) 78 for (G4int j = 0; j < fnvar; ++j)
79 { 79 {
80 y1[j] = y0[j] + h2 * dydx[j]; 80 y1[j] = y0[j] + h2 * dydx[j];
81 } 81 }
82 copy(y0, yTemp); 82 copy(y0, yTemp);
83 83
84 fEquation->RightHandSide(y1, dydx); 84 fEquation->RightHandSide(y1, dydx);
85 } 85 }
86 86
87 // last step 87 // last step
88 // yOut = 0.5 * (y0 + y1 + h * dydx) 88 // yOut = 0.5 * (y0 + y1 + h * dydx)
89 // 89 //
90 for (G4int i = 0; i < fnvar; ++i) 90 for (G4int i = 0; i < fnvar; ++i)
91 { 91 {
92 yOut[i] = 0.5 * (y0[i] + y1[i] + h * dydx[ 92 yOut[i] = 0.5 * (y0[i] + y1[i] + h * dydx[i]);
93 } 93 }
94 } 94 }
95 95
96 void G4ModifiedMidpoint::DoStep( const G4doubl 96 void G4ModifiedMidpoint::DoStep( const G4double yIn[], const G4double dydxIn[],
97 G4double yOut[], G4 97 G4double yOut[], G4double hstep, G4double yMid[],
98 G4double derivs[][G 98 G4double derivs[][G4FieldTrack::ncompSVEC]) const
99 { 99 {
100 G4double y0[G4FieldTrack::ncompSVEC]; 100 G4double y0[G4FieldTrack::ncompSVEC];
101 G4double y1[G4FieldTrack::ncompSVEC]; 101 G4double y1[G4FieldTrack::ncompSVEC];
102 G4double yTemp[G4FieldTrack::ncompSVEC]; 102 G4double yTemp[G4FieldTrack::ncompSVEC];
103 setValue(yIn, Value1D::LabTime, y0, y1, yTem 103 setValue(yIn, Value1D::LabTime, y0, y1, yTemp, yMid, yOut);
104 104
105 const G4double h = hstep / fsteps; 105 const G4double h = hstep / fsteps;
106 const G4double h2 = 2 * h; 106 const G4double h2 = 2 * h;
107 107
108 // y0 = yIn 108 // y0 = yIn
109 copy(y0, yIn); 109 copy(y0, yIn);
110 110
111 // y1 = y0 + h * dydx 111 // y1 = y0 + h * dydx
112 for (G4int i = 0; i < fnvar; ++i) 112 for (G4int i = 0; i < fnvar; ++i)
113 { 113 {
114 y1[i] = y0[i] + h * dydxIn[i]; 114 y1[i] = y0[i] + h * dydxIn[i];
115 } 115 }
116 116
117 // result of first step already gives approx 117 // result of first step already gives approximation
118 // at the center of the interval 118 // at the center of the interval
119 // 119 //
120 if(fsteps == 2) 120 if(fsteps == 2)
121 { 121 {
122 copy(yMid, y1); 122 copy(yMid, y1);
123 } 123 }
124 124
125 fEquation->RightHandSide(y1, derivs[0]); 125 fEquation->RightHandSide(y1, derivs[0]);
126 126
127 // general step 127 // general step
128 // yTemp = y1; y1 = y0 + h2 * dydx; y0 = yTe 128 // yTemp = y1; y1 = y0 + h2 * dydx; y0 = yTemp
129 // 129 //
130 for (G4int i = 1; i < fsteps; ++i) 130 for (G4int i = 1; i < fsteps; ++i)
131 { 131 {
132 copy(yTemp, y1); 132 copy(yTemp, y1);
133 for (G4int j = 0; j < fnvar; ++j) 133 for (G4int j = 0; j < fnvar; ++j)
134 { 134 {
135 y1[j] = y0[j] + h2 * derivs[i-1][j]; 135 y1[j] = y0[j] + h2 * derivs[i-1][j];
136 } 136 }
137 copy(y0, yTemp); 137 copy(y0, yTemp);
138 138
139 // save approximation at the center of the 139 // save approximation at the center of the interval
140 if(i == fsteps / 2 - 1 ) 140 if(i == fsteps / 2 - 1 )
141 { 141 {
142 copy(yMid, y1); 142 copy(yMid, y1);
143 } 143 }
144 144
145 fEquation->RightHandSide(y1, derivs[i]); 145 fEquation->RightHandSide(y1, derivs[i]);
146 } 146 }
147 147
148 // last step 148 // last step
149 // yOut = 0.5 * (y0 + y1 + h * dydx) 149 // yOut = 0.5 * (y0 + y1 + h * dydx)
150 // 150 //
151 for (G4int i = 0; i < fnvar; ++i) 151 for (G4int i = 0; i < fnvar; ++i)
152 { 152 {
153 yOut[i] = 0.5 * (y0[i] + y1[i] + h * deriv 153 yOut[i] = 0.5 * (y0[i] + y1[i] + h * derivs[fsteps-1][i]);
154 } 154 }
155 } 155 }
156 156
157 void G4ModifiedMidpoint::copy(G4double dst[], 157 void G4ModifiedMidpoint::copy(G4double dst[], const G4double src[]) const
158 { 158 {
159 std::memcpy(dst, src, sizeof(G4double) * fnv 159 std::memcpy(dst, src, sizeof(G4double) * fnvar);
160 } 160 }
161 161