[yt-dev] New default particle union?

[Cameron Hummels]

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?  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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>>
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-- 
Cameron Hummels
NSF Postdoctoral Fellow
Department of Astronomy
California Institute of Technology
http://chummels.org
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