Fit function parameters

ROOT
1

Hello,

I have created a TGraphErrors object and I want to fit it with a non pre-defined function (involving logarithm and polynomial). This function has two free parameters, one of which appears both linear and squared.
Is it possible to extract these parameters from the fit?

Manuel

2

See “Access to the fit result” in the TGraph::Fit description.

3

Thanks!! It helped.
Now I have another question. Once I have found the two previous parameters, I want to fix the value of one of them and see how the chi2 distribution varies as a function of the other parameter.
Is it possible to do this?

4

Hi,
Look at http://root.cern.ch/root/html/TF1.html documentation, there you have such functions like FixParameter
Cheers

5

Hi,

I’ll try to be clearer. I have obtained the two parameters, say, a and b from the fit. Now I want to keep one parameter fixed (e.g. a, to do this I know I can use FixParameter) and create the distribution of chi2 vs b. Do I have to do this by myself or can I call a function?

6

Hi all,

finally I solved my problem simply by fixing one of the parameters and varying the other at small steps, within a given interval, and thus redoing the fitting procedure.

Cheers,

Manuel