GammaFun.C: Example showing the usage of the major special math functions (gamma, beta, erf) in ROOT

// Example showing the usage of the major special math functions  (gamma, beta, erf)  in ROOT
// To execute the macro type in:
//
// root[0]: .x GammaFun.C 
//
// It will create one canvas with the representation 
//of the tgamma, lgamma, beta, erf and erfc functions

//
//  Author: Magdalena Slawinska

#include "TMath.h"
#include "TF1.h"
#include "TF2.h"
#include "TSystem.h"
#include "TCanvas.h"
#include "TStyle.h"
#include "TPaveLabel.h"
#include "TAxis.h"
#include "TH1.h" 

void GammaFun() {

gSystem->Load("libMathCore");

gStyle->SetPalette(1);
gStyle->SetOptStat(0);


TF1 *f1a = new TF1("Gamma(x)","ROOT::Math::tgamma(x)",-2,5);
TF1 *f2a = new TF1("f2a","ROOT::Math::lgamma(x)",0,10);
TF2 *f3a = new TF2("Beta(x)","ROOT::Math::beta(x, y)",0,0.1, 0, 0.1);
TF1 *f4a = new TF1("erf(x)","ROOT::Math::erf(x)",0,5);
TF1 *f4b = new TF1("erfc(x)","ROOT::Math::erfc(x)",0,5);

TCanvas *c1 = new TCanvas("c1", "Gamma and related functions",1000,750);

c1->SetFillColor(17);
c1->Divide(2,2);


c1->cd(1);
gPad->SetGrid();
gPad->SetFrameFillColor(19);
 
//setting the title in a label style
TPaveLabel *p1 = new TPaveLabel(.1,.90 , (.1+.50),(.90+.10) ,"ROOT::Math::tgamma(x)", "NDC");
p1->SetFillColor(0);
p1->SetTextFont(22);
p1->SetTextColor(kBlack);

//setting graph 
// draw axis first (use TH1 to draw the frame)
TH1F * h = new TH1F("htmp","",500,-2,5);
h->SetMinimum(-20);
h->SetMaximum(20);
h->GetXaxis()->SetTitleSize(0.06);
h->GetXaxis()->SetTitleOffset(.7);
h->GetXaxis()->SetTitle("x");

h->Draw(); 

// draw the funcitions 3 times in the separate ranges to avoid singularities 
f1a->SetLineWidth(2);
f1a->SetLineColor(kBlue);

f1a->SetRange(-2,-1);
f1a->DrawCopy("same");

f1a->SetRange(-1,0);
f1a->DrawCopy("same");

f1a->SetRange(0,5);
f1a->DrawCopy("same");


p1->Draw();

c1->cd(2);
gPad->SetGrid();
gPad->SetFrameFillColor(19);
TPaveLabel *p2 = new TPaveLabel(.1,.90 , (.1+.50),(.90+.10) ,"ROOT::Math::lgamma(x)", "NDC");
   p2->SetFillColor(0);
   p2->SetTextFont(22);
   p2->SetTextColor(kBlack);
f2a->SetLineColor(kBlue);
f2a->SetLineWidth(2);
f2a->GetXaxis()->SetTitle("x");
f2a->GetXaxis()->SetTitleSize(0.06);
f2a->GetXaxis()->SetTitleOffset(.7);
f2a->SetTitle("");
f2a->Draw();
 p2->Draw();

c1->cd(3);
gPad->SetGrid();
gPad->SetFrameFillColor(19);

TPaveLabel *p3 = new TPaveLabel(.1,.90 , (.1+.50),(.90+.10) ,"ROOT::Math::beta(x, y)", "NDC");
   p3->SetFillColor(0);
   p3->SetTextFont(22);
   p3->SetTextColor(kBlack);
f3a->SetLineWidth(2);
f3a->GetXaxis()->SetTitle("x");
f3a->GetXaxis()->SetTitleOffset(1.2);
f3a->GetXaxis()->SetTitleSize(0.06);
f3a->GetYaxis()->SetTitle("y");
f3a->GetYaxis()->SetTitleSize(0.06);
f3a->GetYaxis()->SetTitleOffset(1.5);
f3a->SetTitle("");
 f3a->Draw("surf1");//option for a 3-dim plot
p3->Draw();

c1->cd(4);
gPad->SetGrid();
gPad->SetFrameFillColor(19);
TPaveLabel *p4 = new TPaveLabel(.1,.90 , (.1+.50),(.90+.10) ,"erf(x) and erfc(x)", "NDC");
   p4->SetFillColor(0);
   p4->SetTextFont(22);
   p4->SetTextColor(kBlack);
f4a->SetTitle("erf(x) and erfc(x)");
f4a->SetLineWidth(2);
f4b->SetLineWidth(2);
f4a->SetLineColor(kBlue);
f4b->SetLineColor(kRed);
f4a->GetXaxis()->SetTitleSize(.06);
f4a->GetXaxis()->SetTitleOffset(.7);
f4a->GetXaxis()->SetTitle("x");
f4a->Draw();
 f4b->Draw("same");//option for a multiple graph plot
f4a->SetTitle("");
p4->Draw();

c1->Update();
 c1->cd();


}