sum rules for hessian PDFs

[RoyStegeman]

When computing the uncertainty on the sum rules for hessian PDFs the standard deviation is taken over the moments computed per eigenvector

https://github.com/NNPDF/nnpdf/blob/050d723fb25e1dae8cf47b0a024c156a730d14bb/validphys2/src/validphys/sumrules.py#L214

[comane]

Hi @RoyStegeman, can you perhaps give more details on why this is a bug.

Should a different formula be used for the computation of how much the sum rules for each eigenvector of a hessian set vary?

[RoyStegeman]

See e.g. eqs. 3 and 4 in https://arxiv.org/pdf/1101.0536.

[scarlehoff]

The sum rules should use https://github.com/NNPDF/nnpdf/blob/050d723fb25e1dae8cf47b0a024c156a730d14bb/validphys2/src/validphys/core.py#L852