[yt-users] Mapping of particle field to the grid

[Nathan Goldbaum]

On Thursday, July 23, 2015, Yi-Hao Chen <ychen at astro.wisc.edu> wrote:

> Hi Nathan,
>
> Thank you for answering the questions during your vacation.
>
> I would be happy to add the smoothing functionality to yt. But I have only
> very vague idea about the difference between "patch-based" and
> "octree-based" data and almost no experience on SPH smoothing. I am not
> sure how far I can go. Is there a good introduction/reference for the
> patch-based AMR?
>
> I've tried the arbitrary_grid data object and can get the deposited array
> for an uniform resolution mesh! My question now is how to map this data
> object onto the AMR grid which has higher resolution in some regions since
> I have to do calculation using both the mesh and particle data. The easiest
> way might be converting my mesh data to a uniform, lower resolution array,
> but it would be great if I can do the other way around, i.e. mapping the
> deposited field in the arbitrary_grid to the AMR mesh.
>

You can generate fields for the "x", "y" and "z" coordinates on the
arbitrary_grid mesh. Once you have that, you can use
trilinear interpolation to estimate the fields you care about anywhere on
the AMR mesh.


> Thank you!
> Yi-Hao
>
>
> On Wed, Jul 22, 2015 at 6:43 PM, Nathan Goldbaum <nathan12343 at gmail.com
> <javascript:_e(%7B%7D,'cvml','nathan12343 at gmail.com');>> wrote:
>
>> After hitting send it occurred to me that this might be an oppudtunity to
>> use the arbitrary_grid data object. This will allow you to create a uniform
>> resolution grid to deposit particle quantities onto that more closely
>> matches your particle resolution.
>>
>> On Wednesday, July 22, 2015, Nathan Goldbaum <nathan12343 at gmail.com
>> <javascript:_e(%7B%7D,'cvml','nathan12343 at gmail.com');>> wrote:
>>
>>> Hi Yi-Hao,
>>>
>>> Enabling more generic particle deposition operators for patch based
>>> datasets is a long term goal of mine. As you've discovered, something like
>>> SPH smoothing has not been implemented yet.
>>>
>>> If you're interested in adding this functionality to yt, I would first
>>> bring this up on the dev mailing list to get some advice. Unfortunately I'm
>>> on vacation at the moment and don't have the bandwidth to offer more
>>> concrete advice.
>>>
>>> Nathan
>>>
>>> On Wednesday, July 22, 2015, Yi-Hao Chen <ychen at astro.wisc.edu> wrote:
>>>
>>>> Dear yt-users,
>>>>
>>>> I am working on FLASH datasets with particles. I have some self-defined
>>>> fields (specifically Lorentz factors) that are stored in the particle data
>>>> and would like to map them onto the mesh grid. I've been trying the
>>>> "add_deposited_particle_field" that is in the dev version. Currently I use
>>>> the "cic" method, in which a particle will populate the nearby 8 cells (in
>>>> 3D). However, since my particles are sparser than the mesh cells, many of
>>>> the cells do not have particles nearby and thus are empty.
>>>>
>>>> I would like to find a way to interpolate for those empty cells, i.e.
>>>> to smooth the particle field. Are there any suggestions or directions I
>>>> should look into?
>>>>
>>>>
>>>> It would also be very helpful if I can get the list of N nearest
>>>> neighbor particles for each cell. I've looked into the nearest neighbor
>>>> function
>>>>
>>>> http://yt-project.org/docs/dev/analyzing/fields.html#computing-the-nth-nearest-neighbor
>>>>
>>>> But it seems that it is implemented only for octree-based data objects
>>>> (and can only perform in a particle-to-particle fashion?), while FLASH data
>>>> are loaded into yt as "patch-based" data object.
>>>>
>>>> http://yt-project.org/doc/developing/creating_frontend.html#data-localization-structures
>>>>
>>>> Is there any function that can get the nearest particle neighbors of
>>>> each cell?
>>>>
>>>> Thank you,
>>>> Yi-Hao
>>>>
>>>> --
>>>> Yi-Hao Chen
>>>> Graduate Student
>>>> Department of Astronomy
>>>> University of Wisconsin-Madison
>>>>
>>>>
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