[yt-dev] New default particle union?

Mon Apr 3 14:06:15 PDT 2017

Quick update: this does appear to work. I ended up going with "nbody"
instead of "n-body" due to the tokenization issue.

For now I'm only including particle types that have a 'particle_mass' field
defined and aren't SPH particle types. In principle a tracer particle could
have this field defined with all values set to zero or a very small number,
so it will be up to the individual frontends to correct that.

On Mon, Apr 3, 2017 at 12:12 PM, Britton Smith <brittonsmith at gmail.com>
wrote:

> Sorry, late to the party. +1, even nbody is ok with me.
>
> On Wed, Mar 29, 2017 at 3:59 PM, Michael Zingale <
> michael.zingale at stonybrook.edu> wrote:
>
>> I think Andrew made some recently.  The caveat is that some BoxLib /
>> AMReX codes do have active particles, Nyx for example.  So it needs to be
>> done at the code-level within the BoxLib/AMReX frontend.
>>
>> On Wed, Mar 29, 2017 at 6:58 PM, Nathan Goldbaum <nathan12343 at gmail.com>
>> wrote:
>>
>>> Ok, that would be pretty easy to customize in the Boxlib frontend (or
>>> any other frontends that have tracer particles).
>>>
>>> Do we have any public test datasets with tracer particles?
>>>
>>>
>>> On Wed, Mar 29, 2017 at 5:56 PM Michael Zingale <
>>> michael.zingale at stonybrook.edu> wrote:
>>>
>>>> yes, passive are just lagrangian tracer particles.  So, for example,
>>>> all of the particle stuff in Castro and Maestro are passive / tracer
>>>> particles, and should probably not get an "n-body" label.
>>>>
>>>> On Wed, Mar 29, 2017 at 6:53 PM, Nathan Goldbaum <nathan12343 at gmail.com
>>>> > wrote:
>>>>
>>>> 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 <(631)%20632-8225>
>>>> *e-mail*: Michael.Zingale at stonybrook.edu
>>>> *web*: http://www.astro.sunysb.edu/mzingale
>>>> github: http://github.com/zingale
>>>>
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>>>>
>>>>
>>>>
>>>> --
>>>> Michael Zingale
>>>> Associate Professor
>>>>
>>>> Dept. of Physics & Astronomy • Stony Brook University • Stony Brook, NY
>>>> 11794-3800
>>>> *phone*:  631-632-8225 <(631)%20632-8225>
>>>> *e-mail*: Michael.Zingale at stonybrook.edu
>>>> *web*: http://www.astro.sunysb.edu/mzingale
>>>> github: http://github.com/zingale
>>>>
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>>>
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>>>
>>
>>
>> --
>> Michael Zingale
>> Associate Professor
>>
>> Dept. of Physics & Astronomy • Stony Brook University • Stony Brook, NY
>> 11794-3800
>> *phone*:  631-632-8225 <(631)%20632-8225>
>> *e-mail*: Michael.Zingale at stonybrook.edu
>> *web*: http://www.astro.sunysb.edu/mzingale
>> github: http://github.com/zingale
>>
>>
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