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1 // 1 //
2 // ******************************************* 2 // ********************************************************************
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4 // * 4 // * *
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17 // * 17 // * *
18 // * This code implementation is the result 18 // * This code implementation is the result of the scientific and *
19 // * technical work of the GEANT4 collaboratio 19 // * technical work of the GEANT4 collaboration. *
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24 // ******************************************* 24 // ********************************************************************
25 // 25 //
26 // 26 //
>> 27 // $Id: G4RandomDirection.hh 106707 2017-10-20 08:30:31Z gcosmo $
27 // 28 //
28 // << 29 //
29 // ------------------------------------------- 30 // ------------------------------------------------------------
30 // GEANT 4 class header file << 31 // GEANT 4 class header file
31 // ------------------------------------------- 32 // ------------------------------------------------------------
32 // Class description: 33 // Class description:
33 // 34 //
34 // Function returning a unit 3-vector homogene 35 // Function returning a unit 3-vector homogeneously randomised over 4pi
35 // solid angle. It can be used in any particle 36 // solid angle. It can be used in any particle scattering methods
36 // instead of: 37 // instead of:
37 // z=R1, x=SQRT(1-R1*R1)*SIN(2*pi*R2), y=SQR 38 // 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 // providing more performant results.
39 40
40 // History: 41 // History:
41 // 19.10.17 E. Tcherniaev, use of G.Marsagl 42 // 19.10.17 E. Tcherniaev, use of G.Marsaglia (1972) method
42 // 06.04.17 E. Tcherniaev, added G4RandomDi 43 // 06.04.17 E. Tcherniaev, added G4RandomDirection(cosTheta)
43 // 15.03.16 E. Tcherniaev, removed unnecess 44 // 15.03.16 E. Tcherniaev, removed unnecessary if and unit()
44 // 18.03.08 V. Grichine, unit radius sphere 45 // 18.03.08 V. Grichine, unit radius sphere surface based algorithm
45 // ~ 2007 M. Kossov, algorithm based on 8 46 // ~ 2007 M. Kossov, algorithm based on 8 Quadrants technique
46 // 47 //
47 // ------------------------------------------- 48 // ------------------------------------------------------------
48 #ifndef G4RANDOMDIR_HH 49 #ifndef G4RANDOMDIR_HH
49 #define G4RANDOMDIR_HH 50 #define G4RANDOMDIR_HH
50 51
51 #include <CLHEP/Units/PhysicalConstants.h> 52 #include <CLHEP/Units/PhysicalConstants.h>
52 53
53 #include "G4ThreeVector.hh" <<
54 #include "Randomize.hh" <<
55 #include "globals.hh" 54 #include "globals.hh"
>> 55 #include "Randomize.hh"
>> 56 #include "G4ThreeVector.hh"
56 57
57 // G.Marsaglia (1972) method 58 // G.Marsaglia (1972) method
58 inline G4ThreeVector G4RandomDirection() 59 inline G4ThreeVector G4RandomDirection()
59 { 60 {
60 G4double u, v, b; 61 G4double u, v, b;
61 do << 62 do {
62 { << 63 u = 2.*G4UniformRand() - 1.;
63 u = 2. * G4UniformRand() - 1.; << 64 v = 2.*G4UniformRand() - 1.;
64 v = 2. * G4UniformRand() - 1.; << 65 b = u*u + v*v;
65 b = u * u + v * v; << 66 } while (b > 1.);
66 } while(b > 1.); << 67 G4double a = 2.*std::sqrt(1. - b);
67 G4double a = 2. * std::sqrt(1. - b); << 68 return G4ThreeVector(a*u, a*v, 2.*b - 1.);
68 return G4ThreeVector(a * u, a * v, 2. * b - <<
69 } 69 }
70 70
71 inline G4ThreeVector G4RandomDirection(G4doubl 71 inline G4ThreeVector G4RandomDirection(G4double cosTheta)
72 { 72 {
73 G4double z = (1. - cosTheta) * G4UniformRa << 73 G4double z = (1. - cosTheta)*G4UniformRand() + cosTheta;
74 G4double rho = std::sqrt((1. + z) * (1. - z) << 74 G4double rho = std::sqrt((1.+z)*(1.-z));
75 G4double phi = CLHEP::twopi * G4UniformRand( << 75 G4double phi = CLHEP::twopi*G4UniformRand();
76 return G4ThreeVector(rho * std::cos(phi), rh << 76 return G4ThreeVector(rho*std::cos(phi), rho*std::sin(phi), z);
77 } 77 }
78 78
79 #endif /* G4RANDOMDIR_HH */ << 79 #endif /* G4RANDOMDIR_HH */
80 80