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: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.On 11/19/2025 8:24 AM, Erik Schnetter wrote:MiguelIf 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.htmlSome 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?-erik -- Erik Schnetter <[email protected]> http://www.perimeterinstitute.ca/personal/eschnetter/ _______________________________________________ Users mailing list [email protected] http://lists.einsteintoolkit.org/mailman/listinfo/users
gc_x_RN_subcycl.pdf
Description: gc_x_RN_subcycl.pdf
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