Problems in ggttgg lhe files after the latest upstream changes (replacing channel by iconfig in select_color)

[valassi]

Hi @oliviermattelaer (cc @roiser), I have rerun the usual tests after the upgrade to the latest mg5amcnlo upstream.

Most tests succeed, but in ggttgg I get differences in the lhe files:

In tmad/logs_ggttgg_mad/log_ggttgg_mad_d_inl0_hrd0.txt:
+ERROR! events.lhe.cpp.1 and events.lhe.ref.1 differ!
+diff /data/avalassi/GPU2023/madgraph4gpuX/epochX/cudacpp/gg_ttgg.mad/SubProcesses/P1_gg_ttxgg/events.lhe.cpp.1 /data/avalassi/GPU2023/madgraph4gpuX/epo$
+3,4c3,4
+<          21   -1    0    0  503  502  0.00000000000E+00  0.00000000000E+00  0.13289043826E+04  0.13289043826E+04  0.00000000000E+00 0. -1.
+<          21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.81223316322E+02  0.81223316322E+02  0.00000000000E+00 0. -1.
+---
+>          21   -1    0    0  505  502  0.00000000000E+00  0.00000000000E+00  0.13289043826E+04  0.13289043826E+04  0.00000000000E+00 0. -1.
+>          21   -1    0    0  502  503 -0.00000000000E+00 -0.00000000000E+00 -0.81223316322E+02  0.81223316322E+02  0.00000000000E+00 0. -1.
+6,8c6,8
+<          -6    1    1    2    0  505  0.39403209480E+02 -0.10079469096E+02  0.28578226692E+03  0.33653337532E+03  0.17300000000E+03 0. -1.
+<          21    1    1    2  504  501 -0.19269775075E+03  0.33434234480E+02  0.26595208036E+03  0.33012237159E+03  0.00000000000E+00 0. -1.
+<          21    1    1    2  505  502  0.20498361398E+02  0.29398294961E+02  0.12436578484E+03  0.12942677855E+03  0.00000000000E+00 0. -1.
+---
+>          -6    1    1    2    0  504  0.39403209480E+02 -0.10079469096E+02  0.28578226692E+03  0.33653337532E+03  0.17300000000E+03 0. -1.
+>          21    1    1    2  504  503 -0.19269775075E+03  0.33434234480E+02  0.26595208036E+03  0.33012237159E+03  0.00000000000E+00 0. -1.
+>          21    1    1    2  505  501  0.20498361398E+02  0.29398294961E+02  0.12436578484E+03  0.12942677855E+03  0.00000000000E+00 0. -1.
+54,56c54,56
+<          -6    1    1    2    0  504  0.12539878316E+03  0.25084537686E+03  0.17266798312E+03  0.37201006747E+03  0.17300000000E+03 0.  1.
+<          21    1    1    2  504  505  0.91559552940E+02 -0.56451043237E+03  0.74367925168E+03  0.93814391719E+03  0.00000000000E+00 0. -1.
+<          21    1    1    2  505  503 -0.59178509296E+01 -0.20888672560E+02  0.16637826240E+02  0.27352785287E+02  0.00000000000E+00 0.  1.
+---
+>          -6    1    1    2    0  505  0.12539878316E+03  0.25084537686E+03  0.17266798312E+03  0.37201006747E+03  0.17300000000E+03 0.  1.

I will try to have a look, but does this ring a bell, any way to interpret this?
Thanks
Andrea

[valassi]

This is from 8e09746 in MR #654

[valassi]

@oliviermattelaer I made some tests and this clearly seems to come from this one
mg5amcnlo/mg5amcnlo@0a1038d

Can you confirm that this is correct and that I should fix the GPU plugin to give the same results?

NB my understanding is that this is causing in Fortran only a change in the color assignments in LHE files?

Thanks
Andrea

[valassi]

I have created and merged a NOOP mg5amcnlo/mg5amcnlo#56 where I created a commit hash that works as-is for the current as-is gpu plugin. This will allow me to merge #654 I hope. Then this #655 will need to be fixed searately... so it stays very much open...

[oliviermattelaer]

I believe that this was the patch that was fixing the issue for ta+ ta- sample for atlas no?

[valassi]

Hi @oliviermattelaer thanks for looking at this :-)

The only ta+ ta- issue I remember (but I still need to look better at some emails) was #645, problems in CKKW. This I actually noted down as "CMS Drell Yan" (I think it was Sapta from CMS, not ATLAS, but I may be wrong). Anyway, that particular one had a fix from a different commit mg5amcnlo/mg5amcnlo@ef334c5.

Or you mean another ta+ ta- issue for ATLAS? Maybe @roiser knows better?

Anyway, the commit which caused the issue is mg5amcnlo/mg5amcnlo@0a1038d . This essentially replaces channel by iconfig in select_color. The commit title is "fix issue with the color selection " but I am not sure where the issue was observed.

Thanks!
Andrea