[yt-dev] advice on implementing halo member particle loading

[Ben Thompson]

+1 for this idea. I have essentially been using yt.sphere data contains
with the virial radius as my way of querying the particles within the halo.
When in fact depending on the halo finder, halos do not necessary have to
be spherical. Likewise rockstar and other halo finders also have machinery
to tell you what particles are currently in the halo too.

On topic of halo finders, how easy do you guys think would it be to
implement other halo finders? Or at least be able to read in the results of
other halo finders? With machinery like this, it would potentially be
easier to "at least" include the results of other halo finders too. I have
been using AHF for a lot of my work recently but am currently working with
a custom version of the pynbody halo catalog (pretty much a direct rip but
using YT to handle the units upon initialisation). I imagine with machinery
like this it would be easier to do so.

Ben.

On Thu, May 7, 2015 at 11:57 AM, Britton Smith <brittonsmith at gmail.com>
wrote:

> Hi everyone,
>
> Myself and one other who should be joining this list soon are interested
> in implementing some new functionality and I would like to solicit some
> advice.
>
> What we have are halo catalog datasets that, for the most part, are
> already loadable in yt.  They are loadable in that each individual halo is
> a particle such that querying the mass field returns the mass of each
> halo.  However, these datasets also store the particles from the simulation
> snapshot that are the members of each halo.  We currently do not have the
> machinery to query them and this is what we would like to add.
>
> It seems the most sensible idea is to create a halo data container such
> that something like the following returns the mass of all the particles in
> a halo:
>
> my_halo = ds.halo(some_id)
> my_halo["particle_mass"]
>
> This is somewhat different from the existing data containers as it is not
> geometric.  The member particles are explicitly known.  I don't have much
> experience with making data containers so I can't tell if this makes things
> easier or harder.  Anyway, this is the plan.
>
> If anyone has reasons this may be too difficult or simply not work, I
> would appreciate hearing them.  Any general advice or other ideas for
> making this functionality work would also be welcome.
>
> Thanks!
>
> Britton
>
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>
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