void example(){
  
  TH1F *h =new TH1F("h","h",10,0,10);
  h->Fill(1.5);
  h->Fill(2.5);

  TCanvas *c = new TCanvas("c","c");
  h->GetXaxis()->SetRangeUser(0.,2.);
  h->Draw();

  TH2F *h2 = new TH2F("h2","h2",10,0,10,10,0,10);
  for(int i1=0;i1<h2->GetNbinsX();i1++){
    for(int i2=0;i2<h2->GetNbinsY();i2++){
      double xval = h2->GetXaxis()->GetBinCenter(i1+1);
      double yval = h2->GetYaxis()->GetBinCenter(i2+1);
      if( (i1+1)!=2 && (i2+1)!=3) h2->Fill(xval,yval);
    }
  }
 
  for(int i1=0;i1<h2->GetNbinsX();i1++){
    for(int i2=0;i2<h2->GetNbinsY();i2++){
      if(h2->GetBinContent(i1+1,i2+1)==0)
	h2->SetBinContent(i1+1,i2+1,-1.);
    }
  }

  TCanvas *c2 = new TCanvas("c2","c2");
  h2->DrawCopy("colz");
  
  TCanvas *c3 = new TCanvas("c3","c3");
  h2->SetContour(1);
  h2->SetContourLevel(0,0);
  h2->Draw("cont3 same");

  h2->GetXaxis()->SetRangeUser(-1.,6.);
  h2->GetYaxis()->SetRangeUser(-1.,6.);


  return;
}