[Yt-dev] Particles

John Wise john.h.wise at nasa.gov
Thu Sep 10 04:27:55 PDT 2009


Hi,

I like the first example the best because usually the user has some  
idea of the volume they're interested in, such as looking for stars or  
tracer particles in a particular halo or searching for all of the  
stars in the simulation.

The dataspace framework is pretty cool because it removes the  
intensive need of searching through the *entire* particle list for  
only (in most cases) a handful of particles.  Of course because this  
feature is new, we'd still have to support searching for certain  
particles if the dataspace doesn't exist.

Cheers,
John

On 10 Sep 2009, at 00:11, Britton Smith wrote:

> I think something like the first example you gave would be the  
> best.  It's definitely more in keeping with the data_object[field]  
> notation for getting grid data.  In a very similar vein, I find it  
> much more intuitive to think of asking for the particles or grid  
> data associated with a particular object than say start with some  
> larger structure for handling particles for the entire pf, and give  
> me only the ones in some sphere or other object (this is my  
> interpretation of the second example you gave).
>
> Additionally, I think particle data-space stuff you done in Enzo is  
> great.  It seems silly to have to read in an entire set of particles  
> only to filter most of them back out, like with star particles.   
> This will also come in handy for other people who are working with  
> tracer particles.
>
> Britton
>
> On Wed, Sep 9, 2009 at 8:47 PM, Matthew Turk <matthewturk at gmail.com>  
> wrote:
> Hi guys,
>
> I've noticed several of you making commits about particles.  (John,
> Britton, looking at you guys.)  In recent versions of Enzo, I stuck in
> a dataspace supplement that pre-computes dataspaces for different
> particle types in each grid, which should makes things really cheap to
> read *only* star particles, or particles of a different type.  I've
> put in support for this in the yt-hg repo, but the biggest problem
> with it was that I couldn't figure out the right way to address it --
> so I'd like to put out there a question to you guys.
>
> In an ideal world, if you have some data object:
>
> data_obj
>
> what is the best way to be able to address particles of different
> types, and only get those particles?  (Let's pretend either that IO is
> cheap, or we have the dataspace hack.)
>
> For instance,
>
> data_object.particles[type]["x"] # for instance
>
> or maybe,
>
> pf.h.particles[type].sphere(...)
>
> or something?  What do you think?  Any off-the-wall ideas?
>
> -Matt
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