Problem with ROOT::Fit::FitResult::Chi2()

ROOT
1

Dear experts,
It seems there is a bug in ROOT::Fit::FitResult::Chi2() method in root versions 6-30-01, 6-30-02.
To show it, I am attaching the tutorial combinedFit.C with one additional line

cout<<" Chi2 = "<<result.Chi2()<<endl;

The output is:

Processing combinedFit.C...
****************************************
Minimizer is Minuit2 / Migrad
MinFCN                    =      131.104
NDf                       =          115
Edm                       =  2.11602e-08
NCalls                    =          225
Par_0                     =       5.5396   +/-   0.0354094
Par_1                     =      4.66089   +/-   0.050106
Par_2                     =   -0.0514037   +/-   0.00108539      (limited)
Par_3                     =      77.2733   +/-   3.93105         (limited)
Par_4                     =           30                         (fixed)
Par_5                     =        4.864   +/-   0.243005
 Chi2 = -1

You can see, that result.Chi2() returns -1 while it returns the correct value 131.104 in older root versions.
combinedFit.C (4.0 KB)

2

I guess @moneta can help.

3

Hi,

Thank you for reporting this issue. I have found the origin of the problem and I will submit a fix for this. As workaround use result.MinFcnValue() to get the chi2 value.

Best regards

Lorenzo

5

This has been fixed after merging [math][fitter] Fix return chi2 when fitting user provided chi2 functions by lmoneta · Pull Request #14359 · root-project/root · GitHub