[Rivet] question to yodamerge

[Frank Siegert]

Hi Hannes,

this particular histogram seems to be normalised to a given integral
(which I don't claim to understand:
0.7*crossSection()*_sumW/sumOfWeights()) instead of scaled
proportional to the cross section like dsigma/dX. This means there is
a priori no clear prescription of how they can be merged from
different runs, and thus the simple yodamerge script fails. If there
is some way to merge these objects even though they are normalised
then you have to write a small Python script yourself which does it.

Note 1: The --assume-normalized switch has an unfortunate naming and
has been a constant source of confusion for users. This has been
discussed before, and I'll state my opinion again:
- the switch should be the default behaviour of yodamerge (because
most of our distributions are of the dsigma/dX type which need it)
- there should be two options to overwrite (/replace) the broken
heuristic of whether something should be merged or added:
--force-merge (if you have multiple identical runs from different
random seeds) vs. --force-add (if you have multiple samples that have
to be added, e.g. electron and muon channel, Np0...Np4, ...).

Note 2: On the proper and automatic run combination for arbitrary
objects (including arbitrarily normalised histograms) we have this
ticket:
https://rivet.hepforge.org/trac/ticket/457

Cheers,
Frank


On 14 April 2015 at 06:57, Hannes Jung <hannes.jung at desy.de> wrote:
> Dear Rivet experts
>
> i use yodamerge to add yoda files from stat independent runs
> with
>
> yodamerge --assume-normalized  .....
>
> now in some cases I get the warning:
>
> WARNING: Abandoning normalized merge of path /CMS_2013_I1256943/d01-x01-y01 because not all inputs have ScaledBy attributes
>
> and the results are weird.
>
> What is wrong there, or what could I check ?
> Thanks a lot
> cheers
> Hannes
>
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