{
   TCanvas *c1 = new TCanvas("c1","A Simple Graph Example",200,10,700,500);
   Double_t x[100], y[100];
   Int_t n = 20;
   for (Int_t i=0;i<n;i++) {
     x[i] = i*0.1;
     y[i] = 10*sin(x[i]+0.2);
   }
   gr = new TGraph(n,x,y);
   gr->SetBit(TGraph::kNotEditable);
   gr->Draw("AC*");

   float xx[2] = {0.3, 1.0};
   float yy[2] = {2, 8};
   TPolyLine *line = new TPolyLine(2, xx, yy);
   line->Draw();
   return c1;
}