G4RandomDirection.hh

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// $Id$
//
// 
// ------------------------------------------------------------
//      GEANT 4 class header file 
// ------------------------------------------------------------
// Class description:
//
// Function 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.

// History:
//    18.03.08 V. Grichine, unit radius sphere surface based algorithm
//      ~ 2007 M. Kossov, algorithm based on 8 Quadrants technique
//
// ------------------------------------------------------------
#ifndef G4RANDOMDIR_HH
#define G4RANDOMDIR_HH

#include <CLHEP/Units/PhysicalConstants.h>

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

inline G4ThreeVector G4RandomDirection()
{
  G4double cosTheta  = 2.*G4UniformRand()-1.;
  G4double sinTheta2 = 1. - cosTheta*cosTheta;
  if( sinTheta2 < 0.)  sinTheta2 = 0.;
  G4double sinTheta  = std::sqrt(sinTheta2); 
  G4double phi       = CLHEP::twopi*G4UniformRand();
  return G4ThreeVector(sinTheta*std::cos(phi),
                       sinTheta*std::sin(phi), cosTheta).unit(); 
}

#endif  /* G4RANDOMDIR_HH */