{
    using namespace RooFit;
    using namespace RooStats;
    
    RooRealVar x("x","dummy obs",0.,1.);
    RooUniform pdf_x("pdf_x","dummy pdf of x",x);
    
    RooRealVar s("s","# of signal",0.,10.);
    RooRealVar b("b","# of background",3.2,0.,10.);
    RooAddPdf pdf_splusb("pdf_splusb","total PDF",RooArgList(pdf_x,pdf_x),RooArgList(s,b));
    
    RooUniform prior_s("prior_s","prior for signal",s);
    RooGaussian prior_b("prior_b","priot for background",b,RooConst(3.2),RooConst(1.4));
    RooProdPdf model("model","constrained model",pdf_splusb,prior_b);
    
    RooWorkspace wspace("wspace");
    ModelConfig cfg(&wspace);
    cfg.SetPdf(model);
    cfg.SetParametersOfInterest(s);
    cfg.SetPriorPdf(prior_s);
    cfg.SetNuisanceParameters(b);
    
    RooPlot *frame = s.frame();
    for (int n=0; n<=4; n++) {
        RooRealVar nevt("nevt","# of observed event",n);
        RooDataSet data("data","data",RooArgSet(x,nevt),WeightVar("nevt"));
        data.add(RooArgSet(x),n);
        
        BayesianCalculator bcalc(data,cfg);
        RooAbsPdf *posterior = bcalc.GetPosteriorPdf();
        posterior->plotOn(frame, LineColor(kRed+n),LineWidth(3));
    }
    frame->Draw();
}