Gabriele Cosmo
80 lines
3.2 KiB
C++
80 lines
3.2 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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//
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//
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// ------------------------------------------------------------
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// GEANT 4 class header file
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// ------------------------------------------------------------
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// Class description:
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//
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// Function returning a unit 3-vector homogeneously randomised over 4pi
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// solid angle. It can be used in any particle scattering methods
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// instead of:
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// z=R1, x=SQRT(1-R1*R1)*SIN(2*pi*R2), y=SQRT(1-R1*R1)*COS(2*pi*R2)
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// providing more performant results.
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// History:
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// 19.10.17 E. Tcherniaev, use of G.Marsaglia (1972) method
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// 06.04.17 E. Tcherniaev, added G4RandomDirection(cosTheta)
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// 15.03.16 E. Tcherniaev, removed unnecessary if and unit()
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// 18.03.08 V. Grichine, unit radius sphere surface based algorithm
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// ~ 2007 M. Kossov, algorithm based on 8 Quadrants technique
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//
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// ------------------------------------------------------------
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#ifndef G4RANDOMDIR_HH
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#define G4RANDOMDIR_HH
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#include <CLHEP/Units/PhysicalConstants.h>
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#include "G4ThreeVector.hh"
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#include "Randomize.hh"
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#include "globals.hh"
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// G.Marsaglia (1972) method
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inline G4ThreeVector G4RandomDirection()
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{
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G4double u, v, b;
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do
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{
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u = 2. * G4UniformRand() - 1.;
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v = 2. * G4UniformRand() - 1.;
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b = u * u + v * v;
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} while(b > 1.);
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G4double a = 2. * std::sqrt(1. - b);
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return G4ThreeVector(a * u, a * v, 2. * b - 1.);
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}
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inline G4ThreeVector G4RandomDirection(G4double cosTheta)
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{
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G4double z = (1. - cosTheta) * G4UniformRand() + cosTheta;
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G4double rho = std::sqrt((1. + z) * (1. - z));
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G4double phi = CLHEP::twopi * G4UniformRand();
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return G4ThreeVector(rho * std::cos(phi), rho * std::sin(phi), z);
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}
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#endif /* G4RANDOMDIR_HH */
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