TProfile::Approximate(kTRUE) not scale invariant

Roofit and RooStats
1

Every couple of years I run into this and hopefully now for the last time :smiley:

The problem:

Error assignment to a bin with just 1 entry, aka variance == 0

The Solution:

Calculate the variance by using the data of all the other bins.

However, the test that determines whether the bin variance == 0 is
not (!) scale invariant:

In Double_t TProfileHelper::GetBinError:

Double_t test = 1;
if (err2 != 0 && neff < 5) test = eprim2*sum/err2;
if (p->fgApproximate && (test < 1.e-4 || eprim2 < 1e-6)) {

should probably be replaced by

if (eprim2 <= 0) {
2

Hi Eddy,

I agree with your suggested change. I will now commit in git

Thanks

Lorenzo