[yt-dev] New default particle union?

Wed Mar 29 15:59:42 PDT 2017

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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-- 
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
github: http://github.com/zingale
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