Fit status


I am looking for the right documentation about fit result but I can’t find it. I am using this code to fit some data :

TFitResultPtr r;
r = gr->Fit("fun_fit", "MS", "e1", 110, 1450);

This is basically using the Minuit algorithm with the MIGRAD technique. In my terminal it sometimes show above the fitted parameters result “STATUS = NOT POSDEF” or “STATUS=OK”. I understand both even though I do not find any references in ROOT documentation. What I would like to do is get the covariance matrix when the status is =OK which only happens when I force the fit multiple times using the fit panel and so it seems I can’t access this fit result informations. Can you help me on that ?

Maybe @moneta knows