Hi Olivier,

Thanks for the update!  I tried with the patch, but the problem persists. I went ahead in the following order

- Copied the patch file which I named “singlecorepatch" into ./MG5_aMC_v2_6_0/madgraph/interface
- Applied the patch using patch madevent_interface.py singlecorepatch. patch Got the output "patching file madevent_interface.py”, and no errors.
- Generated the process from scratch, ./mg5 process_card.dat
- Ran the process exactly as I wrote down in my first post. 

And then pythia8 fails with the error

PYTHIA Abort from Pythia::init: Les Houches Event File not found  

This time I do not get the error "Try turning parallelization off by setting the option nb_core to 1”. Again, the file unweighted_events.lhe in the result folder appears uncompressed after the whole process is done. Is that normal? I thought it needed to be compressed for Pythia8 to find the file. 

I attach the MG5 output and Pythia 8 log file. 

Thanks!

Daniel




> On Sep 13, 2017, at 7:16 AM, Olivier Mattelaer <email address hidden> wrote:
> 
> Hi Daniel,
> 
> 
> Ok looks like that such problem occur only for matched/merged sample.
> I have just pushed a patch in the development version for such problem.
> You can download the patch here:
> http://bazaar.launchpad.net/~mg5core2/mg5amcnlo/2.6.1/diff/282?context=3
> 
> Another way to fix your problem should be to set run_mode on 0 (single
> core) rather than 2 (multicore)
> 
> Cheers,
> 
> Olivier
> 
>> On 11 Sep 2017, at 19:10, Daniel Egana-Ugrinovic <email address hidden> wrote:
>> 
>> ** Description changed:
>> 
>> Hi,
>> 
>> When showering with Pythia8 with just one core, showering fails. The
>> error one gets is
>> 
>> Pythia8 cross-section could not be retreived.
>> Try turning parallelization off by setting the option nb_core to 1.
>> 
>> The given message doesn't make sense, since I am actually running on a
>> single core. Strangely, the problem only arises when working with only
>> one core, with generate_events --nb_core=1. Using generate_events
>> --nb_core=2 fixes the issue (unfortunately, when running on clusters,
>> system administrators usually ask you to avoid multi-threaded code, so
>> - in those cases using nb_core=2 would not help).
>> + in those cases using nb_core=2 would not help). The problem may be that
>> + the file unweighted_events.lhe is not being compressed into a gzip file
>> + unweighted_events.lhe.gz. Since run_shower.sh seems to need a gzipped
>> + lhe file, showering fails.
>> 
>> Further information:
>> Options are set in mg5 with
>> set run_mode 2
>> set nb_core 1
>> save options
>> 
>> Events are being run with madevent:
>> generate_events runname --nb_core=1
>> shower=PYTHIA8
>> 
>> Technical details:
>> Running madgraph 2.6.0
>> Pythia8
>> Python 2.7.13
>> gcc (GCC) 6.2.0
>> 
>> I attach the MG5 output file
>> 
>> Thanks!
>> 
>> Daniel
>> 
>> -- 
>> You received this bug notification because you are subscribed to
>> MadGraph5_aMC@NLO.
>> https://bugs.launchpad.net/bugs/1716425
>> 
>> Title:
>> Showering does not work when running with nb_core=1
>> 
>> Status in MadGraph5_aMC@NLO:
>> New
>> 
>> Bug description:
>> Hi,
>> 
>> When showering with Pythia8 with just one core, showering fails. The
>> error one gets is
>> 
>> Pythia8 cross-section could not be retreived.
>> Try turning parallelization off by setting the option nb_core to 1.
>> 
>> The given message doesn't make sense, since I am actually running on a
>> single core. Strangely, the problem only arises when working with only
>> one core, with generate_events --nb_core=1. Using generate_events
>> --nb_core=2 fixes the issue (unfortunately, when running on clusters,
>> system administrators usually ask you to avoid multi-threaded code, so
>> in those cases using nb_core=2 would not help). The problem may be
>> that the file unweighted_events.lhe is not being compressed into a
>> gzip file unweighted_events.lhe.gz. Since run_shower.sh seems to need
>> a gzipped lhe file, showering fails.
>> 
>> Further information:
>> Options are set in mg5 with
>> set run_mode 2
>> set nb_core 1
>> save options
>> 
>> Events are being run with madevent:
>> generate_events runname --nb_core=1
>> shower=PYTHIA8
>> 
>> Technical details:
>> Running madgraph 2.6.0
>> Pythia8
>> Python 2.7.13
>> gcc (GCC) 6.2.0
>> 
>> I attach the MG5 output file
>> 
>> Thanks!
>> 
>> Daniel
>> 
>> To manage notifications about this bug go to:
>> https://bugs.launchpad.net/mg5amcnlo/+bug/1716425/+subscriptions
> 
> -- 
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1716425
> 
> Title:
>  Showering does not work when running with nb_core=1
> 
> Status in MadGraph5_aMC@NLO:
>  New
> 
> Bug description:
>  Hi,
> 
>  When showering with Pythia8 with just one core, showering fails. The
>  error one gets is
> 
>  Pythia8 cross-section could not be retreived.
>  Try turning parallelization off by setting the option nb_core to 1.
> 
>  The given message doesn't make sense, since I am actually running on a
>  single core. Strangely, the problem only arises when working with only
>  one core, with generate_events --nb_core=1. Using generate_events
>  --nb_core=2 fixes the issue (unfortunately, when running on clusters,
>  system administrators usually ask you to avoid multi-threaded code, so
>  in those cases using nb_core=2 would not help). The problem may be
>  that the file unweighted_events.lhe is not being compressed into a
>  gzip file unweighted_events.lhe.gz. Since run_shower.sh seems to need
>  a gzipped lhe file, showering fails.
> 
>  Further information:
>  Options are set in mg5 with
>  set run_mode 2
>  set nb_core 1
>  save options
> 
>  Events are being run with madevent:
>  generate_events runname --nb_core=1
>  shower=PYTHIA8
> 
>  Technical details:
>  Running madgraph 2.6.0
>  Pythia8
>  Python 2.7.13
>  gcc (GCC) 6.2.0
> 
>  I attach the MG5 output file
> 
>  Thanks!
> 
>  Daniel
> 
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/mg5amcnlo/+bug/1716425/+subscriptions