// NLL vs Chi2 fits
fitgen3()
{
  // Setup a model
  RooRealVar x("x","x",-10,10) ;
  RooRealVar mx("mx","mx",0,-0.5,0.5) ;
  RooRealVar sx("sx","sx",3,2.5,3.5) ;
  RooGaussian gx("gx","gx",x,mx,sx) ;

  RooRealVar y("y","y",-10,10) ;
  RooRealVar my("my","my",0,-0.5,0.5) ;
  RooRealVar sy("sy","sy",3,1,10) ;
  RooGaussian gy("gy","gy",y,my,sy) ;

  RooProdPdf f("f","f",RooArgSet(gx,gy)) ;

  // Generate a toy dataset
  RooDataSet* d = f.generate(RooArgSet(x,y),10000) ;

  // Bin dataset
  x.setFitBins(15) ;
  y.setFitBins(15) ;
  RooDataHist* db = new RooDataHist("db","db",RooArgSet(x,y),*d) ;

  // Construct binned likelihood
  RooNLLVar nll("nll","nll",f,*db) ;
  
  // Start Minuit session on NLL
  RooMinuit m(nll) ;
  m.migrad() ;
  m.hesse() ;
  RooFitResult* r1 = m.save() ;

  // Construct Chi2
  RooChi2Var chi2("chi2","chi2",f,*db) ;

  // Start Minuit session on Chi2
  RooMinuit m2(chi2) ;
  m2.migrad() ;
  m2.hesse() ;
  RooFitResult* r2 = m2.save() ;

  // Print results 
  cout << "result of binned likelihood fit" << endl ;
  r1->Print("v") ;
  cout << "result of chi2 fit" << endl ;
  r2->Print("v") ;
}