G4RandomDirection.hh

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// $Id: G4RandomDirection.hh 97527 2016-06-03 14:59:04Z gcosmo $
//
// 
// ------------------------------------------------------------
//      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:
//    15.03.16 E. Tcherniaev, removed unnecessary if and unit()
//    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 z   = 2.*G4UniformRand() - 1.;  // z = cos(theta)
  G4double rho = std::sqrt((1.+z)*(1.-z)); // rho = sqrt(1-z*z)
  G4double phi = CLHEP::twopi*G4UniformRand();
  return G4ThreeVector(rho*std::cos(phi), rho*std::sin(phi), z);
}

#endif  /* G4RANDOMDIR_HH */