Dario,
Could you send me a running script reproducing this problem?
Rene Brun
Dario Motta wrote:
>
> Dear rooters,
> I have my data in form of a TGraph object and I fit them with a
> user-defined function, indeed a simple double exponential function
> defined as:
> total = new TF1("total","expo(0)+expo(2)",5,100).
> I don't have so far a good estimation of the data-points error, but I
> surprisingly found that the errors on the fit parameters estimated by
> MINUIT (called by TGraph::Fit) are perfectly "reasonable" and independent
> on the normalization of the graphic (i.e. on any arbitrary weight factor
> with which I multiply my y-values). In addition I find that the errors on
> the parameters printed out by MINUIT on the screen (which indeed do depend
> on normalization factors!) are different from those returned by
> fift->GetParError(), that I use.
> I conclude that some special algorithm might be called to estimate default
> errors and to calculate parameters errors. Is my interpretation correct?
> If so, can I have some more information on the algorithm implemented?
>
> I use ROOT 3.04 on a linux PC.
>
> Thanks,
>
> Dario Motta
This archive was generated by hypermail 2b29 : Thu Jan 01 2004 - 17:50:15 MET