# What are weights in a generation process

Asked by Ilirjan Margjeka on 2019-05-10

Hello there,

Dear MG5 writers, I have some questions about the weights for the generations of the events, which might be stupid, but I've got a bit confused about this topic:

1) What are weight in a generation process?
2)What are positive and negative weight? what's the difference between them?
3)How to plot histograms implementing the weight from the generation process?

Thank you in advance!

Kind regards,
Ilirjan

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2019-05-11
 Olivier Mattelaer (olivier-mattelaer) said on 2019-05-11: #1

Hi,

> 1) What are weight in a generation process?

I would suggest you to read section 2 and appendix A of 1607.00763.

> 2)What are positive and negative weight? what's the difference between them?

The difference is the fact that the first one are positive and the others one are negative.
Nothing more.

> 3) How to plot histograms implementing the weight from the generation process?

When your observables arrives in a bin, you add the value of the weight to the associate bin.
Then depending of the normalisation choice for your weight, you might need to rescale all the bin by the total number of events.
To be explicit, If the weight is negative you then substract the absolute value of the weight (which is the same as adding that negative number)

Cheers,

Olivier

> On 10 May 2019, at 17:33, Ilirjan Margjeka <email address hidden> wrote:
>
> New question #680742 on MadGraph5_aMC@NLO:
>
> Hello there,
>
> Dear MG5 writers, I have some questions about the weights for the generations of the events, which might be stupid, but I've got a bit confused about this topic:
>
> 1) What are weight in a generation process?
> 2)What are positive and negative weight? what's the difference between them?
> 3)How to plot histograms implementing the weight from the generation process?
>
> Thank you in advance!
>
> Kind regards,
> Ilirjan
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.