{
    gSystem->Load("libRooFit");
    using namespace RooFit;

    // data as TH1 and then RooDataHist
    TH1F *h1 = new TH1F("h1","h1",100,0,10);
    for(int i = 0; i < 10000; i++)
        h1->Fill(gRandom->Gaus(5,1));

    RooRealVar  x("x","x",0,10);
    RooDataHist dhist("dhist","dhist",x,h1);

    // build RooHistPdf and RooGaussian
    // from RooDataHist
    RooHistPdf  hpdf("hpdf","hpdf",x,dhist);

    RooRealVar  m("m","m",0,10);
    RooRealVar  s("s","s",0,10);
    RooGaussian gaus("gaus","gaus",x,m,s);
    gaus.fitTo(dhist);

    // generate toy MC
    RooDataSet *d1000 = gaus.generate(x,1000);

    // draw things so that I feel happy
    // with what I've done
    RooPlot *frame = x.frame();
    d1000->plotOn(frame);
    hpdf.plotOn(frame);
    gaus.plotOn(frame,LineColor(kRed));
    frame->Draw();

    // ask pdfs for NLL given the toy MC
    cout << "hpdf.createNLL(*d1000).getVal(): " <<
        hpdf.createNLL(*d1000).getVal() << endl;

    cout << "gaus.createNLL(*d1000).getVal(): " <<
        gaus.createNLL(*d1000).getVal() << endl;
}