// example of RooEffProdPdf vs RooProdPdf

void prodTest() { 


   RooRealVar X("X", "X", 0.0, 2.0);

   RooRealVar P("P", "Fit Parameter", -1.0, 1.0);
   RooPolynomial PDF("PDF", "Theory PDF", X, RooArgList(P));

   RooGenericPdf A1("A1", "Acceptance PDF", "X <= 1.0 ? 1.0 : 0.5", RooArgSet(X));
   RooFormulaVar A2("A2", "Acceptance Function", "X <= 1.0 ? 1.0 : 0.5", RooArgSet(X));

   RooProdPdf PDFA1("PDFA1", "Theory * Acceptance PDF", RooArgSet(PDF, A1));
   RooEffProd PDFA2("PDFA2", "Theory * Acceptance Function", PDF, A2);


   auto data = PDFA1.generate(X, 10000); 


   auto plot = X.frame(); 

   data->plotOn(plot); 

   // when using the default the option RooFit::Optimize(2) the  result is wrong!
   PDFA1.fitTo(*data, RooFit::Optimize(1), RooFit::Minimizer("Minuit2")); 

   PDFA1.plotOn(plot); 

   PDFA2.fitTo(*data, RooFit::Minimizer("Minuit2")); 

   PDFA2.plotOn(plot, RooFit::LineColor(kRed)); 

   plot->Draw(); 

}