[Rivet] adding histograms

[Andy Buckley]

On 17/03/11 08:40, Robert King wrote:
> Hi Rivet Experts,
> 
> I expect this is a simple question, but I couldn't see how to do it. I
> want to generate a large MC sample and create histograms using Rivet.
> I do this by splitting the job up into 100 sub jobs. I then want to
> add the histograms that are made for each subjob into one histogram. I
> suppose I could convert the .adia files to root files and add together
> in root but I hoped there might be a method in Rivet already for doing
> this...

Hi Robert,

Unfortunately this can't be done "properly" at the moment, because the
output histograms are just x, y, and error values rather than containing
the sort of weighted moments information that's needed to do a proper
statistical combination. If you convert them to ROOT you'll get TGraphs,
which are the same sort of deal, or TH1Fs in which case the combination
is going to be a bit dodgy.

This has been a bit of a thorn in our side for a while, but it was more
important to keep developing the physics content than to rewrite the
histogramming. That's changing with our next release: we're taking a
couple of months to migrate all the histogramming to a new system which
will support all these good things. But for now it's approximations, I'm
afraid: sorry!

Andy

-- 
Dr Andy Buckley
SUPA Advanced Research Fellow
Particle Physics Experiment Group, University of Edinburgh

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