[yt-dev] New default particle union?

[Nathan Goldbaum]

Sorry, you're using terminology I'm unfamiliar with. Are passive particles
the same thing as tracer particles? If so I agree they should probably be
considered separately from n-body particles. For the derived quantities
that motivated this example, massless particles would also need to be
neglected.

On Wed, Mar 29, 2017 at 5:40 PM Michael Zingale <
michael.zingale at stonybrook.edu> wrote:

> I think the name n-body only makes sense for datasets with active
> particles, not those with passive particles.  The latter are the ones that
> I typically deal with.  So maybe a different name?  or maybe a way for a
> code to register if it is using active or passive particles?
>
> On Wed, Mar 29, 2017 at 5:36 PM, Nathan Goldbaum <nathan12343 at gmail.com>
> wrote:
>
>
>
> On Wed, Mar 29, 2017 at 4:33 PM, Cameron Hummels <chummels at gmail.com>
> wrote:
>
> Wait, so we'd have both an 'all' ftype and an 'n-body' ftype and the
> 'n-body' ftype would just include non-gas particles (ie ones without the
> 'smoothing_length' field)?  I'm assuming this won't add more computational
> load when reading in the dataset?
>
>
> I doubt it. There will just be some more fields in ds.derived_field_list
> (one 'n-body' field for each of the 'all' fields).
>
>
> If that's the case, then I'm +0.5 on it.  I haven't had a need for it up
> to this point, but maybe other people really need it?
>
> On Wed, Mar 29, 2017 at 2:21 PM, John ZuHone <jzuhone at gmail.com> wrote:
>
> +1.
>
> "n_body"?
>
> On Mar 29, 2017, at 5:19 PM, Matthew Turk <matthewturk at gmail.com> wrote:
>
> +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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> --
> Cameron Hummels
> NSF Postdoctoral Fellow
> Department of Astronomy
> California Institute of Technology
> http://chummels.org
>
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> --
> Michael Zingale
> Associate Professor
>
> Dept. of Physics & Astronomy • Stony Brook University • Stony Brook, NY
> 11794-3800
> *phone*:  631-632-8225
> *e-mail*: Michael.Zingale at stonybrook.edu
> *web*: http://www.astro.sunysb.edu/mzingale
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