[yt-dev] New default particle union?

[Matthew Turk]

+1, and I think updating YTEP-0031 is sufficient.  Not sure that "n-body"
specifically is my preference, since it's not tokenizable, but maybe it's
fine.

On Wed, Mar 29, 2017 at 4:18 PM, Nathan Goldbaum <nathan12343 at gmail.com>
wrote:

> Hi all,
>
> I'd like to propose adding a new particle union that should be defined for
> all datasets that include particles. This came up in the context of the
> demeshening work (see https://bitbucket.org/yt_
> analysis/ytep/pull-requests/67 for more details).
>
> Right now many of the derived quantities make a distinction between
> calculating results using just the gas or just the particles or both. Up
> until now they have calculated the results for particles using particle
> fields from the 'all' particle union. This makes perfect sense for AMR data
> but doesn't really make sense for SPH data, since it will double-count SPH
> particles. In fact, I think this is an issue even without the demeshening,
> but the demeshening makes it more starkly apparent.
>
> I'd like to propose defining a new "n-body" particle union (suggestions
> for alternate names are very welcome) that will be defined for all yt
> datasets. This union will be identical to the 'all' particle union for AMR
> data and N-body particle data, but for SPH data will only include the
> particle types that aren't SPH particles (if any). That means the "n-body"
> particle type represents infinitesimal particles but not particles that
> have finite extents (e.g. an SPH particle's smoothing region).
>
> I think this new particle type would probably be generically useful beyond
> just the derived quantities, maybe even more useful than "all". I also kind
> of prefer the name "n-body" to "all" since it more prominently indicates
> that it's associated with particle data.
>
> Please let me know if you have thoughts or suggestions about this
> proposal. I'm happy to draft a YTEP or update YTEP-0031 with more details
> if people want to see that.
>
> -Nathan
>
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