| Geant4 Cross Reference |
1 // -*- C++ -*- 1
2 //
3 // -------------------------------------------
4 // HEP Random
5 // --- erfQ ---
6 // method implementation
7 // -------------------------------------------
8
9 // Contains methods that do not depend on larg
10 //
11 // erfQ (double x)
12
13 // ===========================================
14 // M Fischler - Created 1/26/00.
15 //
16 // ===========================================
17
18 #include "CLHEP/Random/Stat.h"
19 #include <cmath>
20
21 namespace CLHEP {
22
23 double HepStat::erfQ (double x) {
24 //
25 // erfQ is accurate to 7 places.
26 // See Numerical Recipes P 221
27 //
28
29 double t, z, erfc;
30
31 z = std::abs(x);
32 t = 1.0/(1.0+.5*z);
33
34 erfc= t*std::exp(-z*z-1.26551223+t*(1.000023
35 t*(-0.18628806+t*(0.27886807+t*(-1.13520398+
36 t*(-0.82215223+t*0.17087277 ))) ))) )));
37
38 // (The derivation of this formula should be
39
40 if ( x < 0 ) erfc = 2.0 - erfc;
41
42 return 1 - erfc;
43
44 }
45
46
47 } // namespace CLHEP
48
49