[Users] running ML_ADMConstraints with timelevels=1 and no SYNCs

[Erik Schnetter]

The ghost and buffer zones are also used for time interpolation, but since
you suggest to only evaluate the constraints when the coarse level is
active, you are circumventing this.

The largest issue I see is that e.g. a regular L2 norm over the simulation
domain is not very useful. It emphasizes very much the coarse grid, which
is very large, and where the boundary conditions might do strange things to
the constraints. Similarly, you will need to be careful to exclude the
interior of the horizons (see CarpetMask) to avoid looking near the
punctures. CarpetMask is not smooth in time, so looking at the time
evolution of the constraint norm is then also problematic.

You might be more happy if you look e.g. at the "isum" or "inorm2" output.
This output is not weighted by coordinate volume, but by grid cells, so
that the coarse grid is deemphasized.

-erik


On Thu, Sep 22, 2016 at 9:14 PM, Roland Haas <roland.haas at physics.gatech.edu
> wrote:

> Hello all,
>
> I am wondering if there would be anything wrong with running
> ML_ADMConstraints with just a single time level for the constraints as
> well as using no SYNCs for it as long as I set it's calc_every
> parameter to the frequency of the coarsest level.
>
> Obviously this will give my "nonssense" values in the ghost zones,
> buffer zones and boundary (though on the boudary I can just set it to
> zero).
>
> However since the constraints are pure output and nothing ever depends
> on them the bad values only matter if they were to eg show up in the
> norms. It is my recollection that CarpetReduce actually does not use
> any values from the ghost zones (certainly that would be wrong) or
> buffer zones (this may be more recent).
>
> Is there any any other way the "bad" values could make it into the
> norms? Note that I do not worry about 1d, 2d, 3d output for the
> constraints.
>
> Yours,
> Roland
>
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-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/
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