Comment 11 for bug 1769271

Hi,

Ok this was a very difficult issue.
So the code was actually deterministic but it requires additional condition to produce the same sample
1) running on the same computer
2) running on the same path

The randomness is linked to the actual randomness of python which allow code to find element at order 1 in a set
independently of the size of the set. So requesting reproducibility enforces us to slow down the code.
(the loss will likely be negligible but I do not like that)

You will find the patch here:
https://bazaar.launchpad.net/~mg5core1/mg5amcnlo/2.6.6/revision/299

Cheers,

Olivier

On 27 Mar 2019, at 15:18, Hannes <<email address hidden><mailto:<email address hidden>>> wrote:

Hi,

I am setting both seed and python_seed in the run_card.dat in MG5 2.6.5
but the events are still shuffled, is there something I am missing? I
have attached a script to reproduce the issue.

Best wishes,
Hannes

** Attachment added: "run.sh"
  https://bugs.launchpad.net/mg5amcnlo/+bug/1769271/+attachment/5249826/+files/run.sh

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https://bugs.launchpad.net/bugs/1769271

Title:
 Reproducibility problem in 2.6.2 (in combine?)

Status in MadGraph5_aMC@NLO:
 Fix Released

Bug description:
 Dear authors,

 I'm running tests with MG5_aMC 2.6.2 - in case you have a CERN account, it's this one:
 /afs/cern.ch/sw/lcg/external/MCGenerators_lcgcmt67c/madgraph5amc/2.6.2.atlas/x86_64-slc6-gcc47-opt/

 We see some non-reproducibility, even when setting a random number
 seed. I attach a tarball of the cards directories so that you have
 the run, param, and proc cards. For the actual runs, iseed was set to
 1234 (of course, the code resets it to 0 after the run).

 Looking at the LHE files, they seem to contain the same events, but in
 different order. Just diffing the two files, you can see an example
 right away:

 1487a1488,1496
6 1 +8.9242237e-05 3.75379100e+02 7.95049700e-03 1.05265500e-01
      21 -1 0 0 501 502 +0.0000000000e+00 +0.0000000000e+00 +2.1196628570e+01 2.1196628570e+01 0.0000000000e+00 0.0000e+00 -1.0000e+00
       2 -1 0 0 502 0 -0.0000000000e+00 -0.0000000000e+00 -1.6619322556e+03 1.6619322556e+03 0.0000000000e+00 0.0000e+00 -1.0000e+00
      24 2 1 2 0 0 +8.9075749711e+01 +3.5726986208e+01 -1.0898807218e+03 1.1239759236e+03 2.5743150990e+02 0.0000e+00 0.0000e+00
 1000023 1 3 3 0 0 +8.0116545705e+01 +1.1392922116e+02 -6.6081705506e+02 6.8029530983e+02 8.2000000000e+01 0.0000e+00 -1.0000e+00
 1000024 1 3 3 0 0 +8.9592040060e+00 -7.8202234949e+01 -4.2906366674e+02 4.4368061374e+02 8.1000000000e+01 0.0000e+00 1.0000e+00
       1 1 1 2 501 0 -8.9075749711e+01 -3.5726986208e+01 -5.5085490525e+02 5.5915296062e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
</event>
<event>
 1506,1532c1515,1542
 < 6 1 +8.9242237e-05 3.75379100e+02 7.95049700e-03 1.05265500e-01
 < 21 -1 0 0 501 502 +0.0000000000e+00 +0.0000000000e+00 +2.1196628570e+01 2.1196628570e+01 0.0000000000e+00 0.0000e+00 -1.0000e+00
 < 2 -1 0 0 502 0 -0.0000000000e+00 -0.0000000000e+00 -1.6619322556e+03 1.6619322556e+03 0.0000000000e+00 0.0000e+00 -1.0000e+00
 < 24 2 1 2 0 0 +8.9075749711e+01 +3.5726986208e+01 -1.0898807218e+03 1.1239759236e+03 2.5743150990e+02 0.0000e+00 0.0000e+00
 < 1000023 1 3 3 0 0 +8.0116545705e+01 +1.1392922116e+02 -6.6081705506e+02 6.8029530983e+02 8.2000000000e+01 0.0000e+00 -1.0000e+00
 < 1000024 1 3 3 0 0 +8.9592040060e+00 -7.8202234949e+01 -4.2906366674e+02 4.4368061374e+02 8.1000000000e+01 0.0000e+00 1.0000e+00
 < 1 1 1 2 501 0 -8.9075749711e+01 -3.5726986208e+01 -5.5085490525e+02 5.5915296062e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
 < </event>

 I believe that's the same event, but note that the line numbers are ~20 apart -- this event is first in one file and fourth in the other. I believe this indicates some non-reproducibility or a race condition in combine somewhere.

 Because these events then enter programs like Pythia8 -- or even when
 they enter MadSpin -- the events are processed in order, the final
 events then appear random (different seeds are applied to the same
 particles). That means the events are effectively not reproducible
 when processed through, so this is an issue for our bug hunting and
 for various other reasons.

 If you could help us out with this it would be very much appreciated!

 Thanks,
 Zach

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