Doubts on histogram sum

[Wile_E_Coyote]

This looks strange in your case:

fit->Constrain(1,0.0,1.0);               // constrain fraction 1 to be between 0 and 1
fit->SetRangeX(1,15);                    // use only the first 15 bins in the fit

Another approach (not using the TFractionFitter) has been proposed in:

Newbie Fit/RooFit Question

Hi, I’m pretty new to Fit/RooFit, and I need some help to get started with my current project. My goal is to find the best-fit parameters to weigh histograms into the desired shape. This means I have three TH1s (mc1, mc2, data); I want to give mc1 and mc2 different weights to make them fit the shape of data (sth like par[0]*mc1+par[1]*mc2=data maybe by minimizing chi2 between the weighted MC and Data). Since par[0]+par[1] !=1, TFractionFitter does not work for me. Is there any way I can achiev…