void shadeGraph() {
   TCanvas *c1 = new TCanvas("c1","A Simple Graph Example",200,10,700,500);

   c1->SetGrid();
   c1->DrawFrame(0,0,2.2,12);
   
   const Int_t n = 20;
   Double_t x[n], y[n],ymax[n];
   Int_t i;
   for (i=0;i<n;i++) {
     x[i] = 0.1+i*0.1;
     y[i] = 9*sin(x[i]+0.15);
     ymax[i] = y[i] + 0.3;
   }
   TGraph *gr      = new TGraph(n,x,y);
   TGraph *grshade = new TGraph(2*n);
   for (i=0;i<n;i++) {
      grshade->SetPoint(i,x[i],ymax[i]);
      grshade->SetPoint(n+i,x[n-i-1],y[n-i-1]);
   }
   grshade->SetFillStyle(3013);
   grshade->SetFillColor(kBlue);
   grshade->Draw("f");
   gr->Draw("C");
}