change gridpack creation option

[oliviermattelaer]

(question asked by email):

Good afternoon. I hope this mail finds you well and sorry for bothering you with it.

I’m trying to change the accuracy of a gridpack generated at LO with MG5 2.9.5.
I was looking to a similar parameter in the run card as for the NLO case (req_acc) but I cannot find it.

Is there an easy way to accomplish this task?

[oliviermattelaer]

We do not have the equivalent for LO.
Now you can certainly implement it by running the various command that create the gridpack one after the other and changing the requested precision during the survey.

But the point is quite limited since the precision parameter is here (not sure for NLO) per channel and going to higher precision will not improve any more the grid (since the limited number of bin per dimension). Now, I guess that reducing accuracy could make sense to speed-up the creation of large gridpack.

so from the executable ./bin/madevent
(or from the ./bin/mg5_aMC after running "launch MYDIRNAME -i")
the default gridpack creation option is:

survey  run_01 --accuracy=0.01 --points=2000 --iterations=8 --gridpack=.true.
combine_events
store_events
create_gridpack

If precision is an issue, it is likely better to incread the number of (maximum) iterations or to increase the point (at the first iteration, --events are double after each iteration--) rather than decreasing the accuracy (which is used as an early exit)