Re: using TH1::Fit()

From: Rene Brun (Rene.Brun@cern.ch)
Date: Thu Aug 19 1999 - 16:08:25 MEST


Marco van Leeuwen wrote:
> 
> Hi,
> 
> In continuation to my former question, the following:
> 
> 1) Which error values does TH1::Fit() use? Does it use the errors in the
> histogram (GetBinError) and, if no errors are specified, does it use the
> sqrt of the BinContent ?  The answer to this is hidden in an external
> function H1FitChiSquare, I think. Maybe the answer can be added to the
> Fit-howto??
> 

Hi Marco,
Your guess is right. I have added the info to the url "HowtoFit"

> 2) Is there an easy/elegant way to check whether parameters have hit their
> limit? I found abs(cos(fX[i-1])) < 0.001 in mnprin, but isn't there some
> other way?? By the way, what does the second parameter to TMinuit::mnprin()
> do?

The return status from TMinuit is a bit messy. All TMinuit data members
being public(!), you can test the member
   TString fCstatu
In the condition above, this string will contain "parameter at limit"

Rene Brun



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