[Users] Communicated region and active part of the domain

[Erik Schnetter]

Dominik

Carpet calculates these region sizes automatically based on the
parameters. This calculation can fail (and will then sometimes lead to
strange errors such as the one you reported) if either:
- the coarse grid has too few points (since Carpet cannot increase the
coarse grid size)
- there are too many processes used (since Carpet is not always clever
enough to leave some of the processes unused)

It is sometimes surprising how many grid points are needed for a
self-consistent grid setup. For example, with 3 ghost zones and an RK4
operator, the coarse grid needs to have more than 30 grid points or so
at least to contain all ghost and buffer zones around the fine grid.
If there is only a single grid, arbitrarily small domains should be
possible (if you set up the boundaries correctly).

The error messages should probably be improved.

As a remedy, I recommend using fewer MPI processes and/or increasing
the resolution of the coarse grid.

-erik



On Thu, Nov 28, 2019 at 3:41 AM Dominik Guido Rhiem
<s6dorhie at uni-bonn.de> wrote:
>
> Dear all,
>
> in order to decrease the necessary calculations for a simulation, I tried to
> lower the resolution and limit the domain size of the simulation. However, I
> get the error that the communicated region has to be contained within the
> active part of the domain; I don't see where the issue is in my parameter
> file, though. I paid attention that the region size is an integer multiple
> of the resolution and to not extract e.g. gravitational waves from surfaces
> at a larger radius than the region size. I have attached both the error
> file, the output file and the parameter file. (Note that I also use some
> non-standard thorns, e.g. for seeding magnetic fields.)
>
> Sincerely,
> Dominik Rhiem
>
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-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/