source: trunk/source/global/HEPRandom/include/G4RandomDirection.hh @ 835

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// $Id: G4RandomDirection.hh,v 1.3 2006/06/29 19:00:47 gunter Exp $
// GEANT4 tag $Name: geant4-09-01-patch-02 $
//
// 
// ------------------------------------------------------------
//      GEANT 4 class header file 
// ------------------------------------------------------------
// Class description:
//
// Funtion returning a unit 3-vector homogeneously randomised over 4pi
// solid angle. It can be used in any particle scattering methods
// instead of:
//   z=R1, x=SQRT(1-R1*R1)*SIN(2*pi*R2), y=SQRT(1-R1*R1)*COS(2*pi*R2)
// providing more performant results.
// ------------------------------------------------------------
#ifndef G4RANDOMDIR_HH
#define G4RANDOMDIR_HH

#include "globals.hh"
#include "Randomize.hh"
#include "G4ThreeVector.hh"

inline G4ThreeVector G4RandomDirection()
{
  // Randomization in one of 8 Quadrants (x>0, y>0, z>0)
  //
  G4double x=G4UniformRand(), y=G4UniformRand(), z=G4UniformRand();
  G4double r2= x*x+y*y+z*z;
  while(r2>1.||r2<.000001)
  {
    x = G4UniformRand(); y = G4UniformRand(); z = G4UniformRand();
    r2=x*x+y*y+z*z;
  }
  G4double r=std::sqrt(r2), quad=G4UniformRand();

  if(quad>0.5)
  {
    if(quad>0.75)
    {
      if(quad>0.875)    return G4ThreeVector(-x/r,-y/r,-z/r);
      else              return G4ThreeVector(-x/r,-y/r, z/r);
    }
    else
    {
      if(quad>0.625)    return G4ThreeVector(-x/r, y/r,-z/r);
      else              return G4ThreeVector(-x/r, y/r, z/r);
    }
  }
  else
  {
    if(quad>0.25)
    {
      if(quad>0.375)    return G4ThreeVector( x/r,-y/r,-z/r);
      else              return G4ThreeVector( x/r,-y/r, z/r);
    }
    else if(quad>0.125) return G4ThreeVector( x/r, y/r,-z/r);
  }
  return                       G4ThreeVector( x/r, y/r, z/r);
}

#endif  /* G4RANDOMDIR_HH */