[Users] Problems with regridding?

Frank Loeffler knarf at cct.lsu.edu
Thu Feb 25 15:32:05 CST 2016

On Wed, Feb 24, 2016 at 01:51:23PM +0000, Geraint Pratten wrote:
> I've been playing around with grids under the assumption that there is no
> reflection symmetry and I seem to be hitting a problem when Carpet goes to
> regrid. The system evolves for ~ 80M quite happily but it hits a point
> where it attempts to regrid levels 1 and up causing all sorts of havoc,
> notably the measure of the Hamiltonian constraint blows up until the
> simulation gracefully terminates due to NaNs.

I didn't encounter this, but looking at your grid setup I don't see a
problem with level 1. It should have enough points to the outer
boundary - it is the other levels that are much 'tighter', but don't
seem to cause problems. The one difference I see for level 1 is the
different time refinement factor you have between level 0 and level 1
(factor 1), and between all other levels (factor 2). This could be a
hint as to where to look for the cause, but might also be a red herring.
A simple test could be using a factor of 2 there as well. It might
introduce other problems, but if this particular problem goes away when
that level regrids, it would be another hint.

Also, you say that the constraint shoots up: did you only look at the
norms? If so: plot it over the entire domain to see where that happens.
It might just be that refinement boundary, giving you another clue
towards a solution.


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