Fitting with an extended composite p.d.f [RooFit]

Roofit and RooStats
1

Dear RooFit experts,

I’m constructing a composite p.d.f to fit a distribution. The relevant part of the code is shown below:

[code] RooRealVar NumA(“NumA”,“NumA”,0.,NumOfData);
RooExtendPdf extPdf_A(“extPdf_A”,“extPdf_A”,pdf_A,NumA);
RooRealVar NumB(“NumB”,“NumB”,0.,NumOfData);
RooExtendPdf extPdf_B(“extPdf_B”,“extPdf_B”,pdf_B,NumB);

RooAddPdf total(“total”,“total”,RooArgList(extPdf_A,extPdf_B));[/code]

By doing something like NumA.getVal() and NumA.getError() I get the value and the error for each parameter.
Is there a way to get the value and the error for the total result of the fit?
[lets call them Ntotal & d(Ntotal) - by construction Ntotal = NumA+NumB]

Thank you very much in advance.

Cheers–loukas