[Users] BSSN, 8th order accurate -- how much dissipation?

[Erik Schnetter]

On Mon, Apr 8, 2019 at 3:41 PM Steven R. Brandt <sbrandt at cct.lsu.edu> wrote:
>
> I don't know how to answer your question, but I hope to see the
> extensions to Cartoon2D etc. to come back to the toolkit.

They certainly will.

> I'm also wondering if you want to try using PreSync, even if boundary
> conditions and syncs aren't your major problem.

You may or may not be aware that Cartoon2D syncs both before and after
applying boundary conditions for each group, and that it does not work
well with OpenMP. So I am using many MPI processes and have many syncs
in my code.

-erik

> --Steve
>
> On 4/8/2019 12:03 PM, Erik Schnetter wrote:
> > I am trying to set up a binary black hole simulation that uses 8th
> > order accurate finite differencing. (I need the black holes to be
> > highly resolved, and I don't need the wave zone, thus I am not use
> > AMR.) On the other hand, I am using Cartoon2D, and I extended it to
> > support 8th order interpolation.
> >
> > My problem is that I cannot get the simulation started well. After a
> > few (about 70) time steps, the code aborts due to nans. Of course,
> > having modified thorn Cartoon2D, I cannot exclude that I made an error
> > there. On the other hand, I did find some pre-existing errors that I
> > corrected.
> >
> > I wonder: What are good settings for numerical dissipation in this
> > case (ML_BSSN with fdOrder=8)? I see a sample parameter file that uses
> > epsDiss = 0.1; should I expect this to work? Would puncture initial
> > conditions need any kind of special treatment? (I'm using
> > TwoPunctures.)
> >
> > Thanks,
> > -erik
> >
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-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/