G4RandomDirection.hh

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00027 // $Id$
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00029 // 
00030 // ------------------------------------------------------------
00031 //      GEANT 4 class header file 
00032 // ------------------------------------------------------------
00033 // Class description:
00034 //
00035 // Function returning a unit 3-vector homogeneously randomised over 4pi
00036 // solid angle. It can be used in any particle scattering methods
00037 // instead of:
00038 //   z=R1, x=SQRT(1-R1*R1)*SIN(2*pi*R2), y=SQRT(1-R1*R1)*COS(2*pi*R2)
00039 // providing more performant results.
00040 
00041 // History:
00042 //    18.03.08 V. Grichine, unit radius sphere surface based algorithm
00043 //      ~ 2007 M. Kossov, algorithm based on 8 Quadrants technique
00044 //
00045 // ------------------------------------------------------------
00046 #ifndef G4RANDOMDIR_HH
00047 #define G4RANDOMDIR_HH
00048 
00049 #include <CLHEP/Units/PhysicalConstants.h>
00050 
00051 #include "globals.hh"
00052 #include "Randomize.hh"
00053 #include "G4ThreeVector.hh"
00054 
00055 inline G4ThreeVector G4RandomDirection()
00056 {
00057   G4double cosTheta  = 2.*G4UniformRand()-1.;
00058   G4double sinTheta2 = 1. - cosTheta*cosTheta;
00059   if( sinTheta2 < 0.)  sinTheta2 = 0.;
00060   G4double sinTheta  = std::sqrt(sinTheta2); 
00061   G4double phi       = CLHEP::twopi*G4UniformRand();
00062   return G4ThreeVector(sinTheta*std::cos(phi),
00063                        sinTheta*std::sin(phi), cosTheta).unit(); 
00064 }
00065 
00066 #endif  /* G4RANDOMDIR_HH */

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