void example_TEfficiency2D() {

    //canvas only needed for the documentation
//  auto c1 = new TCanvas("c1","",600,400);


  double xbins[] = {0., 1. , 3,  7, 15 };
  double ybins[] = {0., 5,  20 };
  auto hpass = new TH2D("pass","passed events",4,xbins,2,ybins);
  auto htot = new TH2D("pass","total events",4,xbins,2,ybins);
 
  
  bool bPassed;
  TF2 f2("f2","xygaus",0,100,0,100);
  f2.SetParameters(1,0,5,0,4);
  double x,y; 
  for(int i=0; i<1000; ++i)
  {

     f2.GetRandom2(x,y); 
     auto t = gRandom->Rndm();

     if (t < .5) hpass->Fill(x,y);
     htot->Fill(x,y); 

  }

  auto c1 = new TCanvas();
  c1->Divide(1,2);
  c1->cd(1);
  hpass->Draw("COLZ");
  c1->cd(2);
  htot->Draw("COLZ");

  TEfficiency* pEff = new TEfficiency(*hpass,*htot);


  pEff->SetStatisticOption(TEfficiency::kBBayesian);
  pEff->SetConfidenceLevel(0.68);

  auto c2 = new TCanvas();
  pEff->Draw("EY");
  c2->Update(); // needed to get the painted histogram
  auto heff = pEff->GetPaintedHistogram();
  heff->SetMinimum(0.0);
  c2->Update();
  c2->Draw();

 }