[Users] Meeting minutes for 2021-07-08

[Leonardo Rosa Werneck]

Chair: Peter
Minutes: Leo

Present: David, Leo, Miguel, Peter, Roland, Yosef, Zach

* Any SpEC updates? No, Roland will send an email.

* Any updates on the status of LORENE? Not from anyone in the
 call. Roland will email Josh about this.

* Summer school updates? The program is ready. You can find it on the
  ETK summer school site (https://einsteintoolkit.github.io/et2021uiuc/).
  All invited speakers have been contacted. There is still a hole in the
  schedule which the organizers are currently trying to fill.

* David: is there any plans on having a hardware expert for the ETK? No,
  there are those who are able to help, but not someone dedicated to
  only doing that.

* David: what exactly is the configuration script doing? Difficult to
  answer, because the entire process is scripted and involves a
  decision tree. But in a nutshell, a few Perl scripts are called and
  then make is invoked.

* Next ET release: need to find a new release manager.

* Unanswered questions in the mailing list:
  ** http://lists.einsteintoolkit.org/pipermail/users/2021-July/008056.html
     Roland: Likely the answer to the question is simply that there are
     reflections happening at the refinement boundaries. Particularly the
     fact that the constraint violations appear to increase towards the
     corner of the AMR grids is a good indicator that this is being caused
     by spurious reflections and interpolation errors. It is possible to
     mitigate these effects by tweaking some of the parameters.
     Zach: Very hard to answer and reproduce without having the user's
     parameter file. It could be an issue with the con2prim in the hydro
     code, in which e.g. a fluid velocity is coupled to one of the CCZ4
     modes and leads to these large errors. Also, why use CCZ4 here? Has
     BSSN already been tested?

  ** http://lists.einsteintoolkit.org/pipermail/users/2021-July/008060.html
     Roland: The fact that PPM and WENO display different behavior in
     the maximum density over time is not too surprising since the two
     are quite different. However, the fact that WENO and WENO-Z also
     display large differences is a bit strange, as the latter is just a
     slight modification of the former with a few extra things added.
     Zach: I don't really know what to make of the plots. It may be a
     problem with the WENO implementation in GRHydro. Would reply to the
     user: could you please simplify the test a bit? Looking at a BNS is
     too difficult a test to diagnose these issue, so it would be better
     to look at convergence tests for a single NS.
     Roland: Also suspects that the user is using the MHD option in
     GRHydro but with zero magnetic fields.
     Zach: Again, it would be easier for us to understand what the user
     is doing if we had access to their parameter file. Another test
     that could be performed would be to start with a single NS and then
     place a refinement level *inside* the star. All the refinement
     boundary issues should be greatly amplified, but the system should
     still be stable.

Next week's chair: Roland
Next week's minutes: Bill