void graph10000() {
   Double_t x[20000];
   Double_t y[20000];
   for (int i=0; i<20000; i++) {
      x[i]=i/5000.;
      y[i]=sin(i/5000.)*gRandom->Rndm();
   }
   TGraph *gr1=new TGraph(9999, x, y);
   TCanvas* c1=new TCanvas("c9999", "c9999");
   gr1->Draw("ALP");

   TGraph *gr2=new TGraph(20000, x, y);
   TCanvas* c2=new TCanvas("c20000", "c20000");
   gr2->Draw("ALP");
   
}