#include <TGraph.h>
#include <TMultiGraph.h>
#include <TCanvas.h>
#include <TLegend.h>
#include <TROOT.h>
#include <TStyle.h>


void Example(){

TGraph *g1 = new TGraph();
TGraph *g2 = new TGraph();
TGraph *g3 = new TGraph();
	
TCanvas *ccc = new TCanvas();

Int_t i;
for(i=0;i<10;i++){
	g1->SetPoint(i,i,i%3);
	
	g2->SetPoint(i,i,i%4);
	
	g3->SetPoint(i,i,i%2);
	
	}

  ccc->Clear();
  g1->SetMarkerStyle(20);
  g2->SetMarkerStyle(21);
  g3->SetMarkerStyle(22);

	
  g1->SetMarkerColor(2);
  g2->SetMarkerColor(3);
  g3->SetMarkerColor(4);

  TLegend * leg = new TLegend(0.6,0.85,0.95,1);
  leg->AddEntry(g1,"1");
  leg->AddEntry(g2,"1");
  leg->AddEntry(g3,"3");

TMultiGraph *ggg = new TMultiGraph("Esempio","Esempio");

ggg->Add(g1);
ggg->Add(g2);
ggg->Add(g3);

TF1 *ppp = new TF1("ppp","pol0");

gStyle->SetOptFit(1111);

ggg->SetTitle("Esempio");

ggg->Draw("AP");

ggg->Fit(ppp,"V");
//uncomment this to see th workaround I used
/*
char stt[80];
sprintf(stt,"Chisquare/NDF: %f/%d",ppp->GetChisquare(),ppp->GetNDF());

leg->AddEntry(ppp,stt);

leg->Draw();
*/
}