| Geant4 Cross Reference |
1 // 1
2 // *******************************************
3 // * License and Disclaimer
4 // *
5 // * The Geant4 software is copyright of th
6 // * the Geant4 Collaboration. It is provided
7 // * conditions of the Geant4 Software License
8 // * LICENSE and available at http://cern.ch/
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10 // *
11 // * Neither the authors of this software syst
12 // * institutes,nor the agencies providing fin
13 // * work make any representation or warran
14 // * regarding this software system or assum
15 // * use. Please see the license in the file
16 // * for the full disclaimer and the limitatio
17 // *
18 // * This code implementation is the result
19 // * technical work of the GEANT4 collaboratio
20 // * By using, copying, modifying or distri
21 // * any work based on the software) you ag
22 // * use in resulting scientific publicati
23 // * acceptance of all terms of the Geant4 Sof
24 // *******************************************
25 //
26 //
27 //
28 //
29 // -------------------------------------------
30 // GEANT 4 class header file
31 // -------------------------------------------
32 // Class description:
33 //
34 // G4Poisson is the C++ implementation of the
35 // for the generation of Poisson distributed r
36 // adapted to invoke HepRandom from CLHEP for
37 // GPOISS is recognized to be a faster algorit
38 // accurate output, than the algorithm adopted
39
40 // -------------------------------------------
41 #ifndef G4POISSON_HH
42 #define G4POISSON_HH
43
44 #include <CLHEP/Units/PhysicalConstants.h>
45
46 #include "G4Exp.hh"
47 #include "G4Types.hh"
48 #include "Randomize.hh"
49
50 inline G4long G4Poisson(G4double mean)
51 {
52 G4long number = 0;
53 const G4int border = 16;
54 const G4double limit = 2e9;
55
56 if(mean <= border)
57 {
58 G4double position = G4UniformRand();
59 G4double poissonValue = G4Exp(-mean);
60 G4double poissonSum = poissonValue;
61
62 while(poissonSum <= position)
63 {
64 ++number;
65 poissonValue *= mean / number;
66 poissonSum += poissonValue;
67 }
68 return number;
69 } // the case of mean <= 16
70
71 G4double t = std::sqrt(-2. * std::log(G4Unif
72 std::cos(2. * CLHEP::pi * G4Uni
73 G4double value = mean + t * std::sqrt(mean)
74 if(value < 0.)
75 {
76 return 0;
77 }
78 return (value >= limit) ? G4long(limit) : G4
79 }
80
81 #endif /* G4POISSON_HH */
82