MadGraph5_aMC@NLO

Pythia error in run_mode = 0

Asked by Manu

Dear experts,

I am trying to run MadGraph (v3.5.1) in single machine mode, run_mode = 0, and shower the events with Pythia8.
The run does not crash but it becomes stuck on the showering. The Events/run_01/tag_1_pythia8.log file contains the error message pasted below.
I'd be thankful for any advice for how to fix this.

Best,
Manuel

## MadGraph commands:

set run_mode 0
generate p p > t t~
output mgevents
launch
shower=Pythia8

## Pythia log file:

PYTHIA Error: input string not found in settings databases::
    unset PYTHIA8DATA

 PYTHIA Error: input string not found in settings databases::
    unset PYTHIA8DATA
 PYTHIA Abort from Pythia::init: some user settings did not make sense
Counting events in input LHEF, please wait.
Found 100 events in input LHEF.

Start generating events

 PYTHIA Error: input string not found in settings databases::
    unset PYTHIA8DATA
 PYTHIA Abort from Pythia::next: not properly initialized so cannot generate events

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

I'm not a pythia8 expert, but this likely indicate that pythia is not able to find some xml metadata directory or something like that.
So the question is do you have an environment variable
"PYTHIA8DATA"? If you do you can try to
1) unset it and recheck
2) change it to something like
"export PYTHIA8DATA=${PYTHIA8}/share/Pythia8/xmldoc"
where ${PYTHIA8} correspond to the pythia8 version that you want MG5aMC to use (obviously check that such path does exitsts)

if it does not exists, then you can try to setup it.

Cheers,

Olivier

Revision history for this message
Manu (manuphysics) said : 		#2

Hi Olivier,

thanks for your reply. The $PYTHIA8DATA did not exist. I set it up as you suggested but the same issue occurs. I have since checked that this problem exists on several independent machines.

Do you have any other suggestions for what to try or who to contact?

Best
Manuel

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#3

Then my only suggestion would be to contact the authors of pythia via their gitlab.

Cheers,

Olivier

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Sung Hak Lim (sunghak-lim) said : 		#4

Hi Olivier,

I'm experiencing similar issue in MG5 v3.5.3, and the bug looks like due to the uncommented lines in MG5-created pythia8 command file submitted to pythia8 interface of MG5. Could you check that if you have time? I don't see such uncommented lines in multicore pythia8 shower so the showering with nb_core >= 2 works fine.

See 4th and 5th lines of the following:

!
! It is possible to run this card manually with:
! LD_LIBRARY_PATH=/home/starlight/Programs/MG5_aMC_v3_5_3/HEPTools/lib:$LD_LIBRARY_PATH
 unset PYTHIA8DATA
/home/starlight/Programs/MG5_aMC_v3_5_3/HEPTools/MG5aMC_PY8_interface/MG5aMC_PY8_interface tag_1_pythia8.cmd
!
!
! Pythia8 cmd card automatically generated by MadGraph5_aMC@NLO
! For more information on the use of the MG5aMC / Pythia8 interface, visit
! https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LOPY8Merging
!
! ==================
! General parameters
! ==================

Best wishes,
Sung Hak

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#5

Good catch,

Thanks a lot for that, I'm not sure to understand why pythia is crashing due to that but clearly that is solving the situation.
(That I was able to reproduce this time but only on version3 of the code not within the LTS branch)
So I have pushed your fix here (therefore in version 3 only):

https://github.com/mg5amcnlo/mg5amcnlo/commit/e339df2f42edbc0b174e54d7fc7475a85bfbb8fa

Thanks so much for your investigation,

Olivier

Revision history for this message
Sung Hak Lim (sunghak-lim) said : 		#6

You're welcome!

Best wishes,
Sung Hak

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