I’m trying a 4D Unbinned Extended Maximum Likelihood Fit using a toy sample. What I see is that the convergence of the fit changes exactly at 100 events. If my toy ntuple contains 99 events, the fit won’t converge, and I get “MINUIT WARNING IN HESSE ============== Matrix inversion fails.”. If I add one more event, then it works and gives a reasonable result. I would say there’s some parameter causing this behaviour, any idea what may be going on? I could provide the script and a couple of samples if this helps.
Thanks a lot in advance,