void ProdModel()
{

RooRealVar x("x","x",0,6); 
RooRealVar y("y","y",3.95,4.05); 
RooRealVar a0("a0","a0",.60);
RooRealVar a1("a1","a1",0.50);

// Create f(y)
RooPolyVar fy("fy","fy",y,RooArgSet(a0,a1)) ;
// Create CB(x,f(y),s,alpha,n)
RooCBShape model("model","Crystal ball with shifting mean",x,fy,RooFit::RooConst(.1),RooFit::RooConst(1),RooFit::RooConst(1)) ;
//Create "flat" PDF in y: g(y)
RooPolynomial gy("gy","Model for y",y);
// Create plain 2D pdf model(x,sx|y) * g(y)
RooProdPdf condprod("condprod","model(x|y)*gy(y)",gy,RooFit::Conditional(model,x)) ;
//Generate pseudo-data with plain pdf 
Int_t nEvents(1000000);
RooDataSet* Data = condprod.generate(RooArgSet(x,y),nEvents);
// Plot Data and PDF 
RooPlot* xFrame=x.frame();
RooPlot* xFrameZoom=x.frame(2,3);
RooPlot* yFrame=y.frame();
Data->plotOn(xFrame);
Data->plotOn(xFrameZoom);
Data->plotOn(yFrame);
RooAbsReal* condprod_x = condprod.createProjection(y);
RooAbsReal* condprod_y = condprod.createProjection(x);
condprod_x->plotOn(xFrame);
condprod_x->plotOn(xFrameZoom);
condprod_y->plotOn(yFrame);
TCanvas* cy= new TCanvas("cy","cy",350,50,750,550);
yFrame->Draw();
TCanvas* cx= new TCanvas("cx","cx",350,50,750,550);
cx->Divide(2);
cx->cd(1);
xFrame->Draw();
cx->cd(2);
xFrameZoom->Draw();
}