[Users] Grid function "AHFINDERDIRECT::ahmask" has only 1 active time levels on refinement level 1; this is not enough for time interpolation

[Erik Schnetter]

This mask is intended for excision. With excision, AHFinderDirect needs to
make sure that it does not interpolate from within the excised region.
AHFinderDirect copies the excision mask into ahmask, and then interpolates
from ahmask onto the horizon surface. It can thus find out whether an
excised point was used for interpolation. Unfortunately, AHFinderDirect's
code is a bit inflexible, and introducing a mask that is always there is
much easier than changing the number of variables that are interpolated.

This interpolation is the same as is used for the ADMBase variables, and
ahmask thus should have the same number of time levels. You are probably
setting the number of ADMBase timelevels to 1, but some thorn (probably
McLachlan) needs more timelevels and thus increases this number
automatically.

If you set the number of ADMBase timelevels explicitly to the number you
need (probably 3), then ahmask will also have more timelevels, and things
should work. Since you are presumably already using 3 ADMBase timelevels,
this will not change your evolution. And since ahmask will be all zeros
anyway, increasing its number of timelevels should have no ill effect.

If you are looking for horizons at times that require time interpolation,
then 1 timelevel for the ADMBase variables does not suffice.

-erik



On Tue, May 14, 2013 at 9:26 AM, Ian Hinder <ian.hinder at aei.mpg.de> wrote:

>
> On 14 May 2013, at 15:20, Frank Loeffler <knarf at cct.lsu.edu> wrote:
>
> On Tue, May 14, 2013 at 08:35:23AM +0200, Ian Hinder wrote:
>
>  (line 1698 of
> /work/00915/hinder/Cactus/AEI/arrangements/Carpet/CarpetInterp/src/interp.cc):
>
>  -> Grid function "AHFINDERDIRECT::ahmask" has only 1 active time levels
> on refinement level 1; this is not enough for time interpolation
>
>
> Does anyone know why this happens
>
>
> Something tries to interpolate the mask. Evolution shouldn't do that,
> the mask is supposed to be written each (sub-)timestep AFAIR. Now, there
> are other possibilities, as you mentioned below...
>
> and if there is a workaround I can use to get the run going again?
>
>
> The questions is what makes Carpet interpolate, and avoid that.
>
> I have ADMBase::metric_timelevels set to the default, which is 1.
> Should it be 3?
>
>
> It should work with 1.
>
> How about changing the frequency of AHFinderDirect output to match
> the coarsest timelevel?
>
>
> I suspect that this is the cause of your problem: you output in between
> evolution times of the coarsest level, making Carpet interpolate the
> mask. You could (only for the mask probably), output only at full
> coarse level steps, if don't need it more often. You could also try
> (although here I am less sure that this will prevent interpolation) to
> restrict the output of the mask to some of the finer levels only, at
> full time steps of these.
>
>
> I'm not interested in the mask, and I don't output it.  Would something
> still be trying to interpolate this mask?
>
> --
> Ian Hinder
> http://numrel.aei.mpg.de/people/hinder
>
>
> _______________________________________________
> Users mailing list
> Users at einsteintoolkit.org
> http://lists.einsteintoolkit.org/mailman/listinfo/users
>
>


-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.einsteintoolkit.org/pipermail/users/attachments/20130514/6171ea46/attachment.html