Geant4  10.02
G4RandomDirection.hh
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27 // $Id: G4RandomDirection.hh 67970 2013-03-13 10:10:06Z gcosmo $
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29 //
30 // ------------------------------------------------------------
31 // GEANT 4 class header file
32 // ------------------------------------------------------------
33 // Class description:
34 //
35 // Function returning a unit 3-vector homogeneously randomised over 4pi
36 // solid angle. It can be used in any particle scattering methods
37 // instead of:
38 // z=R1, x=SQRT(1-R1*R1)*SIN(2*pi*R2), y=SQRT(1-R1*R1)*COS(2*pi*R2)
39 // providing more performant results.
40 
41 // History:
42 // 18.03.08 V. Grichine, unit radius sphere surface based algorithm
43 // ~ 2007 M. Kossov, algorithm based on 8 Quadrants technique
44 //
45 // ------------------------------------------------------------
46 #ifndef G4RANDOMDIR_HH
47 #define G4RANDOMDIR_HH
48 
49 #include <CLHEP/Units/PhysicalConstants.h>
50 
51 #include "globals.hh"
52 #include "Randomize.hh"
53 #include "G4ThreeVector.hh"
54 
56 {
57  G4double cosTheta = 2.*G4UniformRand()-1.;
58  G4double sinTheta2 = 1. - cosTheta*cosTheta;
59  if( sinTheta2 < 0.) sinTheta2 = 0.;
60  G4double sinTheta = std::sqrt(sinTheta2);
62  return G4ThreeVector(sinTheta*std::cos(phi),
63  sinTheta*std::sin(phi), cosTheta).unit();
64 }
65 
66 #endif /* G4RANDOMDIR_HH */
CLHEP::Hep3Vector G4ThreeVector
G4ThreeVector G4RandomDirection()
#define G4UniformRand()
Definition: Randomize.hh:97
static const double twopi
Definition: G4SIunits.hh:75
double G4double
Definition: G4Types.hh:76