# Is it possible to set nevents > 10^6 in order to decrease the uncertainty?

Asked by Steven Jeremies

Hello,

the run card already tells not to set nevents > 10^6 in a single run. What does a single run mean? It sounds like it
is possible to do multiple runs in order to calculate one cross section. Is this true? I ask because I need to decrease the uncertainity of the result I get even more. Are there any other tips how to do this if 10^6 is the maximum number of samples possible?

Thanks in advance!

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Olivier Mattelaer
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 Revision history for this message Olivier Mattelaer (olivier-mattelaer) said on 2021-08-17: #1

Hi,

You can run as many run as needed and then take the average (or a weighted type of estimator) after that.
You can indeed run multiple run in a row
via the ./bin/madevent executable
(or if you run from ./bin/mg5_aMC via launch dIRECTORYnAME -i)

and then do "multi_run X"
where X is the number of successive run that you want to perform.
Note that this will also merge all the lhef file into a single one, which might be time consuming if you put X too large.

Cheers,

Olivier

> On 17 Aug 2021, at 17:40, Steven Jeremies <email address hidden> wrote:
>
> New question #698405 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/698405
>
> Hello,
>
> the run card already tells not to set nevents > 10^6 in a single run. What does a single run mean? It sounds like it
> is possible to do multiple runs in order to calculate one cross section. Is this true? I ask because I need to decrease the uncertainity of the result I get even more. Are there any other tips how to do this if 10^6 is the maximum number of samples possible?
>
> Thanks in advance!
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

 Revision history for this message Steven Jeremies (minits) said on 2021-08-17: #2

Thanks a lot!

 Revision history for this message Steven Jeremies (minits) said on 2021-08-17: #3

Thanks Olivier Mattelaer, that solved my question.

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