[Rivet] Shape comparisons

[James Henderson]

Hi Andy,

I'm sorry, I seem to have been doing something incorrectly before as now 
everything works as expected after I re-built the rivet analysis. Most 
of the time I want the analysis to normalise to cross-section but there 
are a few times when I just wish to do a shape comparison so I wasn't 
keen to hard-wire the normalisation and yes, this is a personal analysis.

Thanks very much for your useful advice and sorry to waste your time,
Jim


On 13/07/12 14:43, Andy Buckley wrote:
> Hi Jim,
>
> Rivet's been able to do that for some time, but it requires the version
> of HepMC being used to support cross-section passing.
>
> So are you saying that passing an argument of -x 1.0 to the rivet
> command line tool does not override the value that comes from the HepMC
> input? I'd personally consider that to be a bug.
>
> However, modifying the analysis to hard-code the cross-section may not
> be necessary. Is this a personal analysis or a built-in one? If a
> personal one, and you always want to just do shape comparisons, then the
> obvious thing to do is to put some normalize(...) calls in the
> finalize() method. If it's an "official" analysis, or you don't *always*
> want your plots to be normalised, then the rivet-rescale script allows
> you to do post hoc normalisation: it's a bit hacky, since making a
> complete programmatic interface via the command line is ~impossible, but
> should be enough for simple cases like this. People on this mailing list
> should be able to help with the latter if you have trouble.
>
> Finally, just a note that if you're only interested in shapes, then
> there's no need for your analysis to make use of cross-section
> information: just don't make any calls to crossSection(), and remove any
> use of "NeedsCrossSection" from your .info file. But it's always a good
> idea to at least normalise histograms to a fixed area rather than the
> number of events used -- I see the latter all the time, but it just
> makes it harder / more error prone to compare to other samples which may
> be a different size -- perhaps to a subtle extent which doesn't
> immediately set off warning bells!
>
> Cheers,
> Andy
>
>
> On 13/07/12 13:29, James Henderson wrote:
>> Dear Rivet Experts,
>>
>> I have recently updated my Rivet version to 1.8.0 and it seems that now
>> Rivet is able to automatically read in the cross-section of a sample
>> straight from the HepMC file. I was trying to normalise two sample with
>> different actual cross-sections to 1pb in order to do a shape comparison
>> but I can't seem to overwrite the automatic cross-section finder.
>>
>> Is there a way to do such a shape comparison without explicitly altering
>> the .cc file in order to not normalise to the cross-section?
>>
>> Thanks,
>> Jim
>>
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>