TCanvas *exclusiongraph() {
   // Draw three graphs with an exclusion zone.
   //Author: Olivier Couet
   
   TCanvas *c1 = new TCanvas("c1","Exclusion graphs examples",200,10,600,400);
   c1->SetGrid();

   TMultiGraph *mg = new TMultiGraph();
   mg->SetTitle("Exclusion graphs");

   const Int_t n = 35;
   Double_t x1[n], x2[n], x3[n],x[n], y1[n], y2[n], y3[n],y[n];
   Double_t ymax1=-11111,ymax2=-11111,ymax3=-11111;
   Double_t ymin1=1111111,ymin2=1111111,ymin3=1111111;

   for (Int_t i=0;i<n;i++) {
     x1[i]  = i*0.1;
     x2[i]  = x1[i];
     x3[i]  = x1[i]+.5;
     x[i]   = x1[i];
     y1[i] = 10*sin(x1[i]);
     y2[i] = 10*cos(x1[i]);
     y3[i] = 10*sin(x1[i])-2;
     y[i]   = 0;
    
     ymax1 = ymax1 > y1[i] ? ymax1 : y1[i];
     ymax2 = ymax2 > y2[i] ? ymax2 : y2[i];
     ymax3 = ymax3 > y3[i] ? ymax3 : y3[i];
     ymin1 = ymin1 < y1[i] ? ymin1 : y1[i];
     ymin2 = ymin2 < y2[i] ? ymin2 : y2[i];
     ymin3 = ymin3 < y3[i] ? ymin3 : y3[i];
   }

   TGraph *gr1 = new TGraph(n,x1,y1);
   cout <<"real limits "<< ymin1 <<" "<<ymax1<<endl;
   cout <<"histo limits "<< gr1->GetHistogram()->GetMinimum();
   cout << gr1->GetHistogram()->GetMaximum()<<endl;
   cout <<"graph limits "<< gr1->GetMinimum();
   cout << gr1->GetMaximum()<<endl<<endl;
   gr1->SetLineColor(2);
   gr1->SetLineWidth(1504);
   gr1->SetFillStyle(3005);

   TGraph *gr2 = new TGraph(n,x2,y2);
   cout <<"real limits "<< ymin2 <<" "<<ymax2<<endl;
   cout <<"histo limits "<< gr2->GetHistogram()->GetMinimum()<<" ";
   cout << gr2->GetHistogram()->GetMaximum()<<endl;
   cout <<"graph limits "<< gr2->GetMinimum()<<" ";
   cout << gr2->GetMaximum()<<endl<<endl;
   gr2->SetLineColor(4);
   gr2->SetLineWidth(-2002);
   gr2->SetFillStyle(3004);
   gr2->SetFillColor(9);

   TGraph *gr3 = new TGraph(n,x3,y3);
   cout <<"real limits "<< ymin3 <<" "<<ymax3<<endl;
   cout <<"histo limits "<< gr3->GetHistogram()->GetMinimum()<<" ";
   cout << gr3->GetHistogram()->GetMaximum()<<endl;
   cout <<"graph limits "<< gr3->GetMinimum()<<" ";
   cout << gr3->GetMaximum()<<endl<<endl;
   gr3->SetLineColor(5);
   gr3->SetLineWidth(-802);
   gr3->SetFillStyle(3002);
   gr3->SetFillColor(2);

   TGraph *gr = new TGraph(n,x,y);
   cout <<"real limits "<< 0  <<" "<< 0 <<endl;
   cout <<"histo limits "<< gr->GetHistogram()->GetMinimum()<<" ";
   cout << gr->GetHistogram()->GetMaximum()<<endl;
   cout <<"graph limits "<< gr->GetMinimum()<<" ";
   cout << gr->GetMaximum()<<endl<<endl;

   mg->Add(gr1);
   mg->Add(gr2);
   mg->Add(gr3);
   mg->Add(gr);
   mg->Draw("AC");

   return c1;
}