I need a function that, given a chi square value X and the associated number r of degrees of freedom, returns the respective cumulative distribution value. I found it is possible to call it from the ROOT Math libraries, but I need some example as reference… In particular:
- which class have I to write in the header file?
- How do I initialize the function?
Thank you very much!
the function ROOT::Math::ROOT::Math::chisquared_cdf (x, r) where r is the number of degree of freedom, returns the cumulative distribution (i.e. the intergral from 0 to x) of the chi2 distribution. If you need the integral of the right tail (i.e. from x to + inf) you can use ROOT::Math::ROOT::Math::chisquared_cdf_c (x, r)
For using in a compiled program you need to include the header file
and there is not need to do any initialization.
If you want to plot the function, just do:
TF1 *f = new TF1("f","ROOT::Math::chisquared_cdf(x,)",0,10);
f->SetParameter(0,2.); // set the n.d.f to 2
Thank you! It works perfectly!
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