[yt-dev] SPH Smoothing Formulation?

[Matthew Turk]

Hi Cameron,

No, and I just checked, it's not in my draft of the 3.0 paper yet.  It
might be in a YTEP somewhere, but here's the outline.

Here's what it does:

 * Build "mesh" octree from all the particles in a simulation
 * When requested, a "particle" octree is created for particle searching
 * Each cell in the mesh octree is iterated over; neighbor leaves in the
"particle" octree are identified, and the N nearest particles are found.
 (This is a "gather" operation, but because the particle octree is not
balanced, it is not guaranteed to find enough neighbors.)
 * Using the chosen SPH kernel (thanks to Bili Dong, we now have cubic,
quartic, quintic, wendland2, wendland4, and wendland6), the smoothing is
conducted on each cell by looking at all the nearest particles.  This is
implemented in the process function on the class VolumeWeightedSmooth in
yt/geometry/particle_smooth.pyx

I should note that Meagan Lang has implemented a particle kD-tree that
she's integrating to replace the "particle" octree, which will then ensure
a balanced search.  She's verified that when using this, there are no
longer any zero values, and it's also about the same speed, which is pretty
rad.

-Matt

On Thu, Sep 8, 2016 at 12:42 PM, Cameron Hummels <chummels at gmail.com> wrote:

> Hey everyone,
>
> Britton, Devin, and I are writing up the Trident method paper, and we
> wanted to be explicit about how exactly yt deposits SPH field quantities on
> to an octree for particle-based fields.  Are there any formal equations for
> this written down anywhere?  I realize SPH support was added since the
> first yt method paper, so it isn't in there, and I cannot seem to find
> anything in the docs.  I wonder if anyone has anything written down for
> this or if I'm missing it somewhere?
>
> Thanks!
>
> Cameron
>
>
>
> --
> Cameron Hummels
> NSF Postdoctoral Fellow
> Department of Astronomy
> California Institute of Technology
> http://chummels.org
>
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