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Reference Guide
MnMachinePrecision.cxx
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1// @(#)root/minuit2:$Id$
2// Authors: M. Winkler, F. James, L. Moneta, A. Zsenei 2003-2005
3
4/**********************************************************************
5 * *
6 * Copyright (c) 2005 LCG ROOT Math team, CERN/PH-SFT *
7 * *
8 **********************************************************************/
9
11#include "Minuit2/MnTiny.h"
12
13namespace ROOT {
14
15 namespace Minuit2 {
16
17
19 fEpsMac(4.0E-7),
20 fEpsMa2(2.*sqrt(4.0E-7)) {
21
22 //determine machine precision
23 /*
24 char e[] = {"e"};
25 fEpsMac = 8.*dlamch_(e);
26 fEpsMa2 = 2.*sqrt(fEpsMac);
27 */
28
29 // std::cout<<"machine precision eps: "<<Eps()<<std::endl;
30
31 MnTiny mytiny;
32
33 //calculate machine precision
34 double epstry = 0.5;
35 double epsbak = 0.;
36 volatile double epsp1 = 0.; // allow to run this method with fast-math
37 double one = 1.0;
38 for(int i = 0; i < 100; i++) {
39 epstry *= 0.5;
40 epsp1 = one + epstry;
41 epsbak = mytiny(epsp1);
42 if(epsbak < epstry) {
43 fEpsMac = 8.*epstry;
44 fEpsMa2 = 2.*sqrt(fEpsMac);
45 break;
46 }
47 }
48
49}
50
51 } // namespace Minuit2
52
53} // namespace ROOT
double sqrt(double)
VSD Structures.
Definition: StringConv.hxx:21