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1 //
2 // ********************************************************************
3 // * License and Disclaimer *
4 // * *
5 // * The Geant4 software is copyright of the Copyright Holders of *
6 // * the Geant4 Collaboration. It is provided under the terms and *
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15 // * use. Please see the license in the file LICENSE and URL above *
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17 // * *
18 // * This code implementation is the result of the scientific and *
19 // * technical work of the GEANT4 collaboration. *
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24 // ********************************************************************
25 //
26 //
27 //
28 //
29 // ------------------------------------------------------------
30 // GEANT 4 class header file
31 // ------------------------------------------------------------
32 // Class description:
33 //
34 // Function returning a unit 3-vector homogeneously randomised over 4pi
35 // solid angle. It can be used in any particle scattering methods
36 // instead of:
37 // z=R1, x=SQRT(1-R1*R1)*SIN(2*pi*R2), y=SQRT(1-R1*R1)*COS(2*pi*R2)
38 // providing more performant results.
39
40 // History:
41 // 19.10.17 E. Tcherniaev, use of G.Marsaglia (1972) method
42 // 06.04.17 E. Tcherniaev, added G4RandomDirection(cosTheta)
43 // 15.03.16 E. Tcherniaev, removed unnecessary if and unit()
44 // 18.03.08 V. Grichine, unit radius sphere surface based algorithm
45 // ~ 2007 M. Kossov, algorithm based on 8 Quadrants technique
46 //
47 // ------------------------------------------------------------
48 #ifndef G4RANDOMDIR_HH
49 #define G4RANDOMDIR_HH
50
51 #include <CLHEP/Units/PhysicalConstants.h>
52
53 #include "G4ThreeVector.hh"
54 #include "Randomize.hh"
55 #include "globals.hh"
56
57 // G.Marsaglia (1972) method
58 inline G4ThreeVector G4RandomDirection()
59 {
60 G4double u, v, b;
61 do
62 {
63 u = 2. * G4UniformRand() - 1.;
64 v = 2. * G4UniformRand() - 1.;
65 b = u * u + v * v;
66 } while(b > 1.);
67 G4double a = 2. * std::sqrt(1. - b);
68 return G4ThreeVector(a * u, a * v, 2. * b - 1.);
69 }
70
71 inline G4ThreeVector G4RandomDirection(G4double cosTheta)
72 {
73 G4double z = (1. - cosTheta) * G4UniformRand() + cosTheta;
74 G4double rho = std::sqrt((1. + z) * (1. - z));
75 G4double phi = CLHEP::twopi * G4UniformRand();
76 return G4ThreeVector(rho * std::cos(phi), rho * std::sin(phi), z);
77 }
78
79 #endif /* G4RANDOMDIR_HH */
80