[Users] Computing Apparent Horizons

[Zach Etienne]

Dear Mario,

> Thank you for your prompt reply. We are interested in the Einstein
Toolkit tools, particularly in the AHFinderDirect tool, and we installed it
already on our devices following the tutorial on the website "
https://einsteintoolkit.org/". It is a very powerful tool.

Yes, sorry one important detail may not have been very clear in my original
email: The software I pointed to converts the Einstein Toolkit to a library
that any numerical relativity code can interact with. In fact the example
included in the software sets up a spinning black hole in a NRPy+-based
code (which has a different infrastructure than the Einstein Toolkit), and
then calls the Einstein Toolkit library to perform apparent horizon
diagnostics. AHFinderDirect is used for these diagnostics.

Alternatively, you could "simply" write an Einstein Toolkit module (we call
a module a "thorn") that reads in the data from your code onto an Einstein
toolkit grid, then performs the horizon diagnostic. An unformatted data
file could be used for this, so long as your Einstein Toolkit module knows
the format of the data.

Regardless of the technique used, AHFinderDirect needs as input both the
ADM 3-metric gamma_{ij} and extrinsic curvature K_{ij} in Cartesian
coordinates.

Anyway, hope this helps!

-Zach

*     *     *
Zachariah Etienne
Assoc. Prof. of Physics, U. of Idaho
Adjunct Assoc. Prof. of Physics & Astronomy, West Virginia U.
https://etienneresearch.com
https://blackholesathome.net


On Sat, Sep 24, 2022 at 3:31 AM Mario Imbrogno <mario.imbrogno97 at gmail.com>
wrote:

> Dear Prof. Zach Etienne,
>
> Thank you for your prompt reply. We are interested in the Einstein Toolkit
> tools, particularly in the AHFinderDirect tool, and we installed it already
> on our devices following the tutorial on the website "
> https://einsteintoolkit.org/". It is a very powerful tool.
>
> Finding Apparent Horizons (AHs) becomes necessary since we have an article
> under review, and one of the Referees asked us to compute the AHs on
> initial data because he was not convinced that the simulated black holes
> were actually three separate objects, at least initially. To do this, we
> had considered embedding new modules into our full-GR code, but, since
> these should be tested before being used (as you know the procedure for the
> finding of such surfaces is not trivial at all), we thought it was
> appropriate to rely on some other well-tested codes, perhaps the Einstein
> Toolkit, which we will cite in our paper.
>
> So, we thank you for the tips you have given us and we would like to ask
> you if this is all or if there are some other details we need to be aware
> of. For example, our BSSN fields (among which there are the initial
> 3-metric and the extrinsic curvature) are stored in an "UNFORMATTED" data
> file, so could any problems arise about this? At the most, we have to
> convert our data to another format, do we not?
>
> Best regards,
>
> Mario Imbrogno
>
>
>
>
>
>
>
>
> Il giorno ven 23 set 2022 alle ore 17:54 Zach Etienne <zachetie at gmail.com>
> ha scritto:
>
>> Dear Mario,
>>
>> With the help of fellow Einstein Toolkit Maintainer Roland Haas, I wrote
>> a library for reading in Cartesian grid data to AHFinderDirect and
>> QuasiLocalMeasures (additional, isolated horizon diagnostics) from any
>> numerical relativity code. The code is open source, and has been used to
>> analyze horizons from spacetime data generated by NRPy+.
>>
>> Here's how you get it:
>>
>> git clone https://bitbucket.org/zach_etienne/et_minimal_2019_03.git
>> cd et_minimal_2019_03
>> git checkout remotes/origin/with_quasilocalmeasures
>>
>> Check out the README.md
>>
>> -Zach
>>
>> *     *     *
>> Zachariah Etienne
>> Assoc. Prof. of Physics, U. of Idaho
>> Adjunct Assoc. Prof. of Physics & Astronomy, West Virginia U.
>> https://etienneresearch.com
>> https://blackholesathome.net
>>
>>
>> On Fri, Sep 23, 2022 at 6:36 AM Mario Imbrogno <
>> mario.imbrogno97 at gmail.com> wrote:
>>
>>> Dear Einstein-Toolkit community,
>>>
>>> my name is Mario Imbrogno and I am a Ph.D. student at
>>> the University of Calabria (UniCal, Cosenza, Italy) under the
>>> supervision of prof. Sergio Servidio.
>>>
>>> Our research group had developed a spectral code to solve the Einstein
>>> equations via a
>>> pseudo-spectral technique [Meringolo C, Servidio S, and Veltri P "A
>>> spectral method algorithm for numerical
>>> simulations of gravitational fields." Classical and Quantum Gravity 38.7
>>> (2021): 075027], and I am studying different cases of merging two and more
>>> black holes, in vacuum conditions.
>>>
>>> Now I have to compute the apparent horizons (AHs) just for our initial
>>> conditions, and I have
>>> read that the Einstein Toolkit implements the AHFinderDirect, a code
>>> that can detect the AHs.
>>>
>>> My questions are: is there a way to compute such AHs by, just uploading
>>> our 3D cartesian BSSN fields and
>>> using the AHFinderDirect code?
>>>
>>> Who is(are) the user(s) that mainly use(s) such code? Who can I ask?
>>>
>>> Where can I find a detailed guide in which I can learn how to upload my
>>> data using the AHFinderDirect code?
>>>
>>> If someone will help us, there is no problem for us to include as a
>>> co-author of our paper.
>>>
>>> Best regards,
>>>
>>> Mario Imbrogno
>>> _______________________________________________
>>> Users mailing list
>>> Users at einsteintoolkit.org
>>> http://lists.einsteintoolkit.org/mailman/listinfo/users
>>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.einsteintoolkit.org/pipermail/users/attachments/20220924/5a6e5837/attachment.html