l = w::model.createNLL(*d,NumCPU(2)) ;
    RooAbsReal* pll = nll->createProfile(w::a) ;
    RooPlot* framea = w::a.frame(Title("Profile likelihood in parameter a")) ;
    pll->plotOn(framea) ;

    <b>// Construct 2D cumulative distribution function from p.d.f.</b>
    RooAbsReal* cdfxy = w::model.createCdf(RooArgSet(w::x,w::y),ScanNoCdf()) ;
    TH2* hhcdf = cdfxy->createHistogram("x,y",40,40) ;
    hhcdf->SetLineColor(kRed) ;

    TCanvas* c = new TCanvas("c","c",650,650) ;  c->Divide(2,2) ;
    c->cd(1) 