Inverse function of Prob

ROOT
1

Hello,
can I find, under Root, the inverse function of TMath::Prob(chi2,Ndof)?
Should be done like TMath::Inverse(prob, Ndof) , returning a chi^2 value.

2

Hi,
the inverse function of the cumulative of the chi2 is ROOT::Math::chisquared_quantile(prob, ndf).
TMath::Prob is the complement of the chi2 cumulative distribution (right tail integral), so the inverse function is

ROOT::Math::chisquared_quantile_c(prob, ndf)

See also project-mathlibs.web.cern.ch/pro … tFunc.html
or in chapter 13 of the User guide (root.cern.ch/download/doc/13MathLibraries.pdf )

These functions are defined in the header file “Math/DistFunc.h”

Lorenzo