void gminus () {
   c1 = new TCanvas("c1","A Simple Graph Example",200,10,700,500);
   c1->SetGrid();
   c1->SetTopMargin(0.15);
   
   const Int_t n = 20;
   Double_t x[n], y[n];
   for (Int_t i=0;i<n;i++) {
     x[i] = -i*0.5;
     y[i] = -2+10*sin(x[i]+0.2);
   }
   gr = new TGraph(n,y,x);
   gr->SetMarkerStyle(21);
   gr->SetTitle("a rotated graph");
   gr->Draw("ACP");
   TH1 *frame = gr->GetHistogram();
   gr->GetXaxis()->SetLabelOffset(99);
   gr->GetYaxis()->SetLabelOffset(99);
   c1->Update();
   
   //draw an axis at the right side
   TGaxis *ar = new TGaxis(gPad->GetUxmax(),gPad->GetUymin(),
         gPad->GetUxmax(), gPad->GetUymax(),
         gPad->GetUymin(), gPad->GetUymax(),510,"+L");
   ar->Draw();
   ar->SetTitle("the right axis title");
   ar->CenterTitle();      
   //draw an axis at the top
   TGaxis *at = new TGaxis(gPad->GetUxmin(),gPad->GetUymax(),
         gPad->GetUxmax(), gPad->GetUymax(),
         gPad->GetUxmin(), gPad->GetUxmax(),510,"-");
   at->Draw();
   at->SetTitle("the top axis title");
   at->CenterTitle();      
}