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
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