Gridpacks multiple instances

Asked by Amin Aboubrahim on 2018-01-09

Hi Olivier,

1) I am using gridpacks to generate tt~ samples. The thing is that I cannot run separate jobs of the same gridpack on several nodes. It seems that madevent cannot have multiple instances.
Is it possible to override this and get rid of RunWeb? It seems odd to use the gridpack only once per node.

2) Also I am generating some QCD samples and are divided in bins of HT. I have noticed that higher bins require more time to generate the same number of events. Does that make sense? My first bin was quick but the others are taking too much time.

Thank you,

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Olivier Mattelaer
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Hi Amin,

1) It is possible in 2.6.1 if you set the full gridpack directory in read-only mode ( you can use a chmod for that).
In that case, you have to execute the gridpack from different (fully empty) directory and call the executable from that directory.
The generated events will then be created in each directory.

2) This is a typical phase-space integration problem, by adding cut you increase the variance of the function and therefore you need to evaluate more matrix-element to reach the same level of accuracy. Did you use the latest version of the code? In that one, we try to include information from such cuts in a smarter way to speed-up the generation but this is not even a factor of two speed up.

My advise if you need large HT bin would be to investigate the biassing option.



Amin Aboubrahim (amin83) said : #2

Hi Olivier,

1) I forgot about that. I have seen it implemented before and with older versions too. From what you're saying it looks like it is only implemented in 2.6.1 ??

2) I am currently using 2.6.0. I'm not familiar with biasing. I need to read about this.

3) One more question: when the gridpack generation is over, the summary that appears on the html page seems to include a number under "Events". Now the command line screen shows zero events generated but the html shows something else. What is that number?

Thanks a lot.


Hi Amin,

1)I confirm that a gridpack cannot be in read-only mode before 2.6.1. This is a fully new option that cannot be working before (this is unlikely that some non-core developers created a patch for this since this was related to deep change in the code).

3) The number of events set on the command line screens is hardcoded to zero to avoid confusion.
But in the code computing cross-section and generating events are correlated (you can not really do one without the other one).
So for each channel, we have some events generated and the associated efficiency to generate those and those number appears in the html indeed.

Amin Aboubrahim (amin83) said : #4

Thanks Olivier Mattelaer, that solved my question.