mathcoreSpecFunc.C

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/// \file
/// \ingroup tutorial_math
/// \notebook
/// Example macro describing how to use the special mathematical functions
/// taking full advantage of the precision and speed of the C99 compliant
/// environments. To execute the macro type in:
///
/// ~~~{.cpp}
/// root[0] .x mathcoreSpecFunc.C
/// ~~~
///
/// It will create two canvases:
///
///   1. one with the representation of the tgamma, lgamma, erf and erfc functions
///   2. one with the relative difference between the old ROOT versions and the
///      C99 implementation (on obsolete platform+compiler combinations which are
///      not C99 compliant it will call the original ROOT implementations, hence
///      the difference will be 0)
///
/// The naming and numbering of the functions is taken from
/// [Matt Austern, (Draft) Technical Report on Standard Library Extensions, N1687=04-0127, September 10, 2004](A HREF="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1687.pdf")
///
/// \macro_image
/// \macro_code
///
/// \author Andras Zsenei
 
#include "TF1.h"
#include "TSystem.h"
#include "TCanvas.h"
 
void mathcoreSpecFunc() {
 
   TF1 *f1a = new TF1("f1a","ROOT::Math::tgamma(x)",0,20);
   TF1 *f1b = new TF1("f1b","abs((ROOT::Math::tgamma(x)-TMath::Gamma(x))/ROOT::Math::tgamma(x))",0,20);
 
   TF1 *f2a = new TF1("f2a","ROOT::Math::lgamma(x)",0,100);
   TF1 *f2b = new TF1("f2b","abs((ROOT::Math::lgamma(x)-TMath::LnGamma(x))/ROOT::Math::lgamma(x))",0,100);
 
   TF1 *f3a = new TF1("f3a","ROOT::Math::erf(x)",0,5);
   TF1 *f3b = new TF1("f3b","abs((ROOT::Math::erf(x)-TMath::Erf(x))/ROOT::Math::erf(x))",0,5);
 
   TF1 *f4a = new TF1("f4a","ROOT::Math::erfc(x)",0,5);
   TF1 *f4b = new TF1("f4b","abs((ROOT::Math::erfc(x)-TMath::Erfc(x))/ROOT::Math::erfc(x))",0,5);
 
 
   TCanvas *c1 = new TCanvas("c1","c1",800,600);
 
   f1a->SetLineColor(kBlue);
   f1b->SetLineColor(kBlue);
   f2a->SetLineColor(kBlue);
   f2b->SetLineColor(kBlue);
   f3a->SetLineColor(kBlue);
   f3b->SetLineColor(kBlue);
   f4a->SetLineColor(kBlue);
   f4b->SetLineColor(kBlue);
 
   c1->Divide(2,2);
 
   c1->cd(1);
   f1a->Draw();
   c1->cd(2);
   f2a->Draw();
   c1->cd(3);
   f3a->Draw();
   c1->cd(4);
   f4a->Draw();
 
 
   TCanvas *c2 = new TCanvas("c2","c2",800,600);
 
   c2->Divide(2,2);
 
   c2->cd(1);
   f1b->Draw();
   c2->cd(2);
   f2b->Draw();
   c2->cd(3);
   f3b->Draw();
   c2->cd(4);
   f4b->Draw();
 
}