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>> 1 // $Id:$
1 // -*- C++ -*- 2 // -*- C++ -*-
2 // 3 //
3 // ------------------------------------------- 4 // -----------------------------------------------------------------------
4 // HEP Random 5 // HEP Random
5 // --- erfQ --- 6 // --- erfQ ---
6 // method implementation 7 // method implementation file
7 // ------------------------------------------- 8 // -----------------------------------------------------------------------
8 9
9 // Contains methods that do not depend on larg 10 // Contains methods that do not depend on large tables.
10 // 11 //
11 // erfQ (double x) 12 // erfQ (double x)
12 13
13 // =========================================== 14 // =======================================================================
14 // M Fischler - Created 1/26/00. 15 // M Fischler - Created 1/26/00.
15 // 16 //
16 // =========================================== 17 // =======================================================================
17 18
18 #include "CLHEP/Random/Stat.h" 19 #include "CLHEP/Random/Stat.h"
19 #include <cmath> 20 #include <cmath>
20 21
21 namespace CLHEP { 22 namespace CLHEP {
22 23
23 double HepStat::erfQ (double x) { 24 double HepStat::erfQ (double x) {
24 // 25 //
25 // erfQ is accurate to 7 places. 26 // erfQ is accurate to 7 places.
26 // See Numerical Recipes P 221 27 // See Numerical Recipes P 221
27 // 28 //
28 29
29 double t, z, erfc; 30 double t, z, erfc;
30 31
31 z = std::abs(x); 32 z = std::abs(x);
32 t = 1.0/(1.0+.5*z); 33 t = 1.0/(1.0+.5*z);
33 34
34 erfc= t*std::exp(-z*z-1.26551223+t*(1.000023 35 erfc= t*std::exp(-z*z-1.26551223+t*(1.00002368+t*(0.37409196+t*(0.09678418+
35 t*(-0.18628806+t*(0.27886807+t*(-1.13520398+ 36 t*(-0.18628806+t*(0.27886807+t*(-1.13520398+t*(1.48851587+
36 t*(-0.82215223+t*0.17087277 ))) ))) ))); 37 t*(-0.82215223+t*0.17087277 ))) ))) )));
37 38
38 // (The derivation of this formula should be 39 // (The derivation of this formula should be obvious.)
39 40
40 if ( x < 0 ) erfc = 2.0 - erfc; 41 if ( x < 0 ) erfc = 2.0 - erfc;
41 42
42 return 1 - erfc; 43 return 1 - erfc;
43 44
44 } 45 }
45 46
46 47
47 } // namespace CLHEP 48 } // namespace CLHEP
48 49
49 50