[Users] ADMMass Issue

[Erik Schnetter]

Gwyneth

You can use the thorn QuasiLocalMeasures, and apply it to a large
surface (that is obviously not a horizon), but still a bit away from
the outer boundary. Many quantities calculated by QuasiLocalMeasures
make sense away from the horizon. I recommend looking at e.g. the
Hawking mass there. The Hawking mass (and other quasi-local mass
definitions) are generalisations of the ADM mass that also make sense
at finite differences. In general, they have lower errors than the ADM
mass formula itself when calculated at a finite difference; the ADM
mass has errors proportional to 1/r when evaluated at a finite radius.

The example parameter file "qlm-ce-ks-boosted.par" might help you get
started. If you are interested in pursuing this, please ask on the
mailing list or on our Slack channel, or on our weekly phone calls.
(I'll be travelling tomorrow morning and will miss that call.)

-erik


On Sun, Jan 29, 2017 at 5:41 AM, Gwyneth Allwright
<allgwy001 at myuct.ac.za> wrote:
> Hi All,
>
> I've been trying to use the ADMMass thorn to calculate the ADM mass for a
> binary black hole system. The initial ADM mass given by TwoPunctures is
> 0.989, but ADMMass returns 0.031 (using both of the available methods).
>
> Does anyone know what could be going wrong? Alternatively, are there other
> thorns that can be used to calculate the ADM mass?
>
> Thanks in advance!
>
> Gwyneth
>
>
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-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/