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25 //
26 /// \file eventgenerator/particleGun/src/PrimaryGeneratorAction2.cc
27 /// \brief Implementation of the PrimaryGeneratorAction2 class
28 //
29 //
30 //
31 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
32 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
33
34 #include "PrimaryGeneratorAction2.hh"
35
36 #include "PrimaryGeneratorAction.hh"
37
38 #include "G4Event.hh"
39 #include "G4ParticleDefinition.hh"
40 #include "G4ParticleGun.hh"
41 #include "G4ParticleTable.hh"
42 #include "G4PhysicalConstants.hh"
43 #include "G4SystemOfUnits.hh"
44 #include "Randomize.hh"
45
46 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
47
48 PrimaryGeneratorAction2::PrimaryGeneratorAction2(G4ParticleGun* gun) : fParticleGun(gun)
49 {
50 // energy distribution
51 //
52 InitFunction();
53 }
54
55 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
56
57 void PrimaryGeneratorAction2::GeneratePrimaries(G4Event* anEvent)
58 {
59 // uniform solid angle
60 G4double cosAlpha = 1. - 2 * G4UniformRand(); // cosAlpha uniform in [-1,+1]
61 G4double sinAlpha = std::sqrt(1. - cosAlpha * cosAlpha);
62 G4double psi = twopi * G4UniformRand(); // psi uniform in [0, 2*pi]
63 G4ThreeVector dir(sinAlpha * std::cos(psi), sinAlpha * std::sin(psi), cosAlpha);
64
65 fParticleGun->SetParticleMomentumDirection(dir);
66
67 // set energy from a tabulated distribution
68 //
69 // G4double energy = RejectAccept();
70 G4double energy = InverseCumul();
71 fParticleGun->SetParticleEnergy(energy);
72
73 // create vertex
74 //
75 fParticleGun->GeneratePrimaryVertex(anEvent);
76 }
77 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
78
79 void PrimaryGeneratorAction2::InitFunction()
80 {
81 // tabulated function
82 // Y is assumed positive, linear per segment, continuous
83 //
84 fNPoints = 16;
85 const G4double xx[] = {37 * keV, 39 * keV, 45 * keV, 51 * keV, 57 * keV, 69 * keV,
86 71 * keV, 75 * keV, 83 * keV, 91 * keV, 97 * keV, 107 * keV,
87 125 * keV, 145 * keV, 159 * keV, 160 * keV};
88
89 const G4double yy[] = {0.000, 0.077, 0.380, 2.044, 5.535, 15.077, 12.443, 14.766,
90 17.644, 18.518, 17.772, 14.776, 8.372, 3.217, 0.194, 0.000};
91
92 // copy arrays in std::vector and compute fMax
93 //
94 fX.resize(fNPoints);
95 fY.resize(fNPoints);
96 fYmax = 0.;
97 for (G4int j = 0; j < fNPoints; j++) {
98 fX[j] = xx[j];
99 fY[j] = yy[j];
100 if (fYmax < fY[j]) fYmax = fY[j];
101 };
102
103 // compute slopes
104 //
105 fSlp.resize(fNPoints);
106 for (G4int j = 0; j < fNPoints - 1; j++) {
107 fSlp[j] = (fY[j + 1] - fY[j]) / (fX[j + 1] - fX[j]);
108 };
109
110 // compute cumulative function
111 //
112 fYC.resize(fNPoints);
113 fYC[0] = 0.;
114 for (G4int j = 1; j < fNPoints; j++) {
115 fYC[j] = fYC[j - 1] + 0.5 * (fY[j] + fY[j - 1]) * (fX[j] - fX[j - 1]);
116 };
117 }
118
119 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
120
121 G4double PrimaryGeneratorAction2::RejectAccept()
122 {
123 // tabulated function
124 // Y is assumed positive, linear per segment, continuous
125 // (see Particle Data Group: pdg.lbl.gov --> Monte Carlo techniques)
126 //
127 G4double Xrndm = 0., Yrndm = 0., Yinter = -1.;
128
129 while (Yrndm > Yinter) {
130 // choose a point randomly
131 Xrndm = fX[0] + G4UniformRand() * (fX[fNPoints - 1] - fX[0]);
132 Yrndm = G4UniformRand() * fYmax;
133 // find bin
134 G4int j = fNPoints - 2;
135 while ((fX[j] > Xrndm) && (j > 0))
136 j--;
137 // compute Y(x_rndm) by linear interpolation
138 Yinter = fY[j] + fSlp[j] * (Xrndm - fX[j]);
139 };
140 return Xrndm;
141 }
142
143 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
144
145 G4double PrimaryGeneratorAction2::InverseCumul()
146 {
147 // tabulated function
148 // Y is assumed positive, linear per segment, continuous
149 // --> cumulative function is second order polynomial
150 // (see Particle Data Group: pdg.lbl.gov --> Monte Carlo techniques)
151
152 // choose y randomly
153 G4double Yrndm = G4UniformRand() * fYC[fNPoints - 1];
154 // find bin
155 G4int j = fNPoints - 2;
156 while ((fYC[j] > Yrndm) && (j > 0))
157 j--;
158 // y_rndm --> x_rndm : fYC(x) is second order polynomial
159 G4double Xrndm = fX[j];
160 G4double a = fSlp[j];
161 if (a != 0.) {
162 G4double b = fY[j] / a, c = 2 * (Yrndm - fYC[j]) / a;
163 G4double delta = b * b + c;
164 G4int sign = 1;
165 if (a < 0.) sign = -1;
166 Xrndm += sign * std::sqrt(delta) - b;
167 }
168 else if (fY[j] > 0.) {
169 Xrndm += (Yrndm - fYC[j]) / fY[j];
170 };
171 return Xrndm;
172 }
173
174 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
175