GammaFun.C File Reference

Detailed Description

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

#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->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",800,700);

   c1->Divide(2,2);

   c1->cd(1);
   gPad->SetGrid();

   //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 functions 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();
   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();

   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();
   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();
}

Author

Magdalena Slawinska

Definition in file GammaFun.C.