seed issue for decay-chain
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
MadGraph5_aMC@NLO |
Won't Fix
|
Low
|
Unassigned |
Bug Description
Using vanilla MG v2.8.2, I ran the following two scripts:
generate p p > t t~ QED=0 QCD=2
output test_nodecay
launch test_nodecay
set nevents 1000
set iseed 12345
launch test_nodecay
set nevents 1000
set iseed 12345
launch test_nodecay
set nevents 1000
set iseed 12345
launch test_nodecay -i
print_results --path=
generate p p > t t~ QED=0 QCD=2, t > w+ b, t~ > w- b~
output test_decay
launch test_decay
set nevents 1000
set iseed 12345
launch test_decay
set nevents 1000
set iseed 12345
launch test_decay
set nevents 1000
set iseed 12345
launch test_decay -i
print_results --path=
The first script, which doesn't decay the tops, produces the following cross sections:
run_01 tag_1 503.307 1.75095850431 1000
run_02 tag_1 503.307 1.75095850431 1000
run_03 tag_1 503.307 1.75095850431 1000
as expected, given the random seed is the same in each run.
On the other hand, adding the decay chain as in the second script:
run_01 tag_1 484.54 1.6126228715 1000
run_02 tag_1 482.07 1.51073567367 1000
run_03 tag_1 482.07 1.51073567367 1000
So it seems that something is at play here, with the decay syntax, that somehow ignores the choice of iseed in the first run?
Changed in mg5amcnlo: | |
status: | New → Confirmed |
importance: | Undecided → Low |
A further issue that may or not be related to this bug (if not, I will open a new report), when doing the second and subsequent runs, the run card has different formatting than the first run (the beam polarisation options appear but they are not present in the runcard in the first run).
I'm guessing that this is to do with how the cards are generated and there is something different between the generation that happens when an output directory is first created, and when a new run is started after the first one.
Cheers,
Jay