[yt-dev] New default particle union?

[Nathan Goldbaum]

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