How can use chisquare fit in roofit?

ROOT
1

Hello, all

I would like to use chisquare fit in roofit.
I couln’t find it in user guild.
Could anyone show some example code?

2

Hi,

you can use the chi2 fit in Roofit by using the RooChi2Var class.
Attached is an example to perfrom a Gaussian Chi2 fit to an histogram.

However, if you have an unweighted histogram the recommended way (and default in RooFit) is to do a binned likelihood fit.
I would use the Chi2 only when the bins represent a set of points with gaussian distributed errors

Cheers,

Lorenzo
testRooFitChi2.C (1.12 KB)

3

Thank you very much, moneta

And I have a further question.

When I fill a histogram, I use user-defined bin contents and errors like this

In such case, I think the error of each bin should be user-defined error not the poisson error given by default.
To do so, the code should be modified as follows.

Is it right?

Thanks in advance