[Rivet] Advice for unusual truth analysis

[Robert King]

Hi Frank,

Thanks very much for pointing this out. I will try this and may contact you
again if I have problems.

Robert

On 30 May 2011 20:24, Frank Siegert <frank.siegert at cern.ch> wrote:

> Hi all,
>
> I think you are missing an important point here: As soon as you switch MPI
> off in the first event, than your second event will look completely
> different at the ME level because it gets a completely different random
> number (less random numbers being used if MPI is off).
>
> So to really do what you are trying to do, you will need to use a
> (undocumented) Sherpa feature of writing out random number seeds for *all*
> events into a file by specifying:
>
>  EVENT_SEED_MODE=2
>  EVENT_SEED_FILE=seeds.txt
>
> and then read them in the next run (e.g. with MPI off) by
>
>  EVENT_SEED_MODE=1
>  EVENT_SEED_FILE=seeds.txt
>
> To make the seed files smaller, you could also compile Sherpa with
> --enable-gzip in which case they'll be gzipped.
>
> Of course then you'll still need to find a way of comparing these event by
> event with Rivet as discussed below.
>
> Frank
>
>
> On 30/05/11 19:17, Robert King wrote:
>
>> Hi,
>>
>> Thanks for that suggestion. I have already edited an analysis myself so
>> I can probably workout how to add a text file output, and then write a
>> python script that will parse the output of this into some sensible
>> comparison.
>>
>> Cheers
>>
>> Robert
>>
>> On 30 May 2011 18:01, Daniel Weyh <weyh at physik.hu-berlin.de
>> <mailto:weyh at physik.hu-berlin.de>> wrote:
>>
>>    Hi Robert,
>>
>>    I'd guess it will not be possible "on the fly".
>>    Rivet takes a single HepMC-Event, analyzes it and fills histograms
>>    with the result.
>>    For what you want to do, you need to load two events from two
>>    different sources (I guess Sherpa cannot serve you alternatingly
>>    with MPI on/off and the same random seed for two consecutive events)...
>>
>>    The solution I have in mind - if you really need event-to-event
>>    comparison - is a bit dirty (I think) but should work:
>>    1. In your Rivet analysis create a file-stream as member of your
>>    analysis (during init). (Remember to close in finalize() ;-) )
>>    2. Do your analysis. During analyze append the number in question to
>>    your file (filestream << num_of_jets << endl;)
>>    3. Run Sherpa another time with same random seed (I guess you know
>>    how to or check the Sherpa man), output as in 2. but in another file.
>>    4. Analyze the two text files line by line externally. (<-- question
>>    to the others: are there python classes in Rivet which make creating
>>    an .aida by hand painless - to use Rivets plot facilities later on?)
>>    Or: Change 3 to read from the file created in 2 and store the
>>    differences in a histogram.
>>    As always depending on your needs.
>>    (How often you need it, automated or manually, how many observables
>>    (if not only #jets)...)
>>
>>    The files shouldn't be to big. I guess order(10^6) runs = 10^6 lines
>>    * (1byte (newline)+10byte (precision fp)) ~ order(10 MB).
>>
>>    This procedure requires you to write an analysis on your own (or at
>>    least to change the one you would have used for single-run).
>>    I hope this is not a problem for you - otherwise don't hesitate to ask.
>>
>>
>>    Good luck,
>>    Daniel
>>
>>
>>    Am 30.05.2011 um 17:54 schrieb Robert King:
>>
>>     > Dear Rivet Experts,
>>     >
>>     > I have a slightly unusual truth level analysis and I hope you can
>>    advise me as to whether it is possible in Rivet. I have a limited
>>    experience with Rivet and it's not clear to me how one would/could
>>    do this.
>>     >
>>     > I would like to generate identical Sherpa samples (i.e. use the
>>    same random number seeds) one with MPI on and another with it off. I
>>    would then like to compare event by event the number of jets each
>> event.
>>     > Is it possible to do this event by event comparison in Rivet?
>>     >
>>     > Many thanks for you advice
>>     >
>>     > Robert
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>>
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