Unexpected Hamiltonian violation from Carpet boundaries, using CCZ4

[KennethZen]

While using CCZ4 to simulate a single star, the Hamiltonian constraint violation initially came from the star surface as expected, but after some time, the violation was dominated by areas near corners of refinement levels (by Carpet) as shown in following figures, which were strange. Any suggestions?

Thanks and regards,

KZ

[Roland Haas]

Peter Diener addressed some of this in the mailing list: http://lists.einsteintoolkit.org/pipermail/users/2021-July/008064.html

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It is expected that the mesh refinement boundaries will reflect Hamiltonian constraint violations. From what you have provided us, it is not clear whether the level of constraint violations that you see is a cause of concern. You specifically mention CCZ4, but have you tried with BSSN? Does the constraint violations look better, the same, or worse with BSSN?

It is also possible that an issue like this might be caused by some other problem potentially related to parameter settings, so in order to investigate this can you provide your thornlist and parameter file?

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[Roland Haas]

In the ET call from 2021-08-05 Peter reported on having looked further into this and it seems that the issue was eventually tracked down to missing dissipation setting in the parameter file.

Unless objected I will close this ticket as “resolved” after 2021-08-13.