hi all,
i haven’t been able to join the weekly calls lately, but i wanted to
bring this up again.
i recall that the problem is that, unless i’m missing something, the
electric constraint isn’t converging at all in a very simple setting of
a static charged black hole setup. this could be a real issue,
especially since referees often ask for convergence tests and plots (and
thus this could affect potential publications).
i’m happy to help dig into this further, but i’m not super familiar with
Carpet's internals. should i file a bug report, or is someone already
looking into it?
thanks,
Miguel
On 19/11/2025 17:33, [email protected] wrote:
hi Erik, all,
thanks for your input. for this specific example the grid is not moving
at all, so i was expecting it to be a simpler setting than the case with
binary BHs...
is it then expected to see all that noise propagating out of the buffer
region and contaminating the whole grid in such a short amount of time
(plot attached)? this is a bit uncomfortable, since the convergence on
the electric constraint violation is completely lost... if it were a
matter of dropping from 4th to 2nd order (as is the case in the L2 norm
of the Hamiltonian constraint) i'd be fine with it, but a complete lack
of convergence is difficult to justify...
thanks,
Miguel
On 19/11/2025 16:23, Erik Schnetter wrote:
On Nov 19, 2025, at 10:26, Steven Brandt via Users
<[email protected]> wrote:
On 11/19/2025 8:24 AM, Erik Schnetter wrote:
Miguel
If I recall correctly, Ian Hinder studied convergence of black hole
simulations with subcycling in time in great detail. The Einstein
Toolkit gallery example for GW150914 contains the respective
distilled knowledge. https://einsteintoolkit.org/gallery/bbh/index.html
Some important details that I recall:
- You can regrid only when the fine and coarse grids are aligned
- You cannot use time interpolation at all. You need to use enough
buffer zones for all the RK substeps for all the fine timesteps for
each coarse time step. With 3 ghost zones and RK4 you need 21 buffer
zones.
Does no time interpolation mean no dense output? That didn't exist
when Ian did these tests, right?
Output doesn't affect time evolution, so it doesn't matter which way
you output things. Of course, if you use second-order accurate
interpolation to output a quantity you cannot expect 4th order
convergence for these quantities. If you output time-interpolated
values of e.g. the lapse then you should check convergence only for
the fine grid values of the lapse there, not for the interpolated
coarse grid values.
-erik
--
Erik Schnetter <[email protected]>
http://www.perimeterinstitute.ca/personal/eschnetter/
_______________________________________________
Users mailing list
[email protected]
http://lists.einsteintoolkit.org/mailman/listinfo/users
_______________________________________________
Users mailing list
[email protected]
http://lists.einsteintoolkit.org/mailman/listinfo/users
_______________________________________________
Users mailing list
[email protected]
http://lists.einsteintoolkit.org/mailman/listinfo/users
