Problem with constrain

Hi All,

I am using the roofit to fit the MC PDFs to data. The data is fake data which is the sum of all PDFs. In fitting, the data is fitted to 8 PDFs. Fromthese 8, two have external constraint( I called them backgrounds) and 6 are float. Fit works perfectly when the number of backgrounds are high and I can use any number for constraint. but when the number of backgrounds are not high, the fit fails when I want to apply low constraints (less than certain amount it fails). I need to apply low constraint, but I don’t know how to fix this problem. Any thought?
I attached the piece of my code I used to constrain and fit the data to MCPDFs. If I choose less than 0.40 for constraint, it won’t work.
roofit_short.C (856 Bytes)