Hi all,
I noticed in 5.22 the reported errors on the fit parameters have changed with respect to 5.20. Root used to build a Chi2 function assuming 1 as the errors, pass it to MINUIT, and then scale the errors so that one gets Chi2/ndof=1.
In 5.22 it does scale the errors but not using the formula it used to be, namely sigma = sigma_fit * sqrt(chi2/(ndof-1)).
Before I submit a bug report, does anybody have a good explanation of why this was changed?
- Moritz