Hi, I don't have any experience with Minuit from root, but lots of experience with Minuit as a stand-alone. I'm responding because your messages look very familliar, and often don't really indicate a problem. Apart from the invalid errors, do the fitted parameters seem reasonable? If so, you might try to recompute the errors some other way. Often asking for Minos errors solves that problem, though there may be a faster way if you're worried about doing hundreds of thousands of fits. I see that TMinuit::mnmnos() is provided as a hook to compute Minos errors, which can be retrieved by mnerrs(...). Minos will scan your chi^2 function to find +1 unit from the minimum on both sides, and return asymmetric errors. This is valuable for those cases where either the chi^2 really isn't parabolic at the minimum or, more often, when Minuit fixates on some tiny numerical roundoff glitch which wrecks the covariance matrix. - Topher Michael Groys wrote: > Dear rooters, > I'm using TMinuit class with some complex theoretical function > for minimization of chi2 for set of data points. > Often I get following messages: > MIGRAD FAILS TO FIND IMPROVEMENT > MIGRAD TERMINATED WITHOUT CONVERGENCE. > Changing of initial values and errors doesn't help. > What can be done to avoid this problem? > I'am interesting in parameter errors. > But errors that minuit returns in this case are invalid. > Thanks, > Michael > >
This archive was generated by hypermail 2b29 : Thu Jan 01 2004 - 17:50:11 MET