Convergence failure in Minuit Combined Fitter

Roofit and RooStats
1

Hello,
I am using minuit to do a number (~1000) of fits of the same function to data. However most return with a failure to converge. When I look at the status value of the fit, the fits are almost entirely 3. Which tells me" status = 3 : Edm is above max". I also often get the error that the “line search has failed”.

I have heard that the line search failure (which leads to Edm being above max) is mostly caused by an error in the function being minimized. However since not all the the fits fail this leads me to believe the function is not the issue.

What are the other possibilites that would cause this to happen?

thanks!

2

Hi,
Normally the error you get is caused to a numerical error in the function to be minimized, thus the function is not evaluated at a sufficient precision. For example this can happen when a numerical integration is used in evaluating the function. If it is not done to the required accuracy, it can cause such errors in Minuit.
I would suggest you to try to check your function and try to minimize its numerical error

Best Regards

Lorenzo