[yt-dev] Matching points to grids

[John ZuHone]

Chris,

Since last night I've developed a working depth-first approach which is *reasonably* fast, but I think it depends on your definition of reasonable. :) It just did a FLASH dataset with ~7000 blocks and 10^6 points in about 4 minutes. 

I'm going to try it out on a few more datasets, and I'm hoping to issue a PR for it today or tomorrow. 

Best,

John

On Nov 16, 2012, at 6:21 PM, Christopher Moody <cemoody at ucsc.edu> wrote:

> Hi John, 
> I tried writing a cython routine that matched particles to grids a while back. It works in the opposite order as a recursive octree-like gridding. It starts with the highest-level most-refined grids, recording the grid ID that each particle belongs to. It skips previously gridded particles as it progresses to coarser grids. It's likely not faster than depth-first approach.
> 
> It could be helpful, but it's terribly slow, despite several attempts to speed it up. 
> Check out  assign_particles_to_cell_lists() in yt-hg/yt/utilities/lib/CICDeposit.pyx
> 
> chris  
> 
> 
> On Fri, Nov 16, 2012 at 11:30 AM, Matthew Turk <matthewturk at gmail.com> wrote:
> Hi John,
> 
> I think that would work fine for Enzo, we'd just need to iterate over
> root grids.
> 
> -Matt
> 
> On Fri, Nov 16, 2012 at 2:28 PM, John ZuHone <jzuhone at gmail.com> wrote:
> > Hi Matt,
> >
> > Would it work just to start at the top-level grids and then work down the tree, checking the children as you go? I know this would work for FLASH, but I'm not certain it would work for Enzo.
> >
> > John
> >
> > On Nov 16, 2012, at 2:14 PM, Matthew Turk <matthewturk at gmail.com> wrote:
> >
> >> Hi John,
> >>
> >> That's the ideal way, but we don't yet have the code to do that.  I
> >> would like to do that.  The fastest method would be to create a new
> >> version of find_values_at_points (which accepts an array) and make itj
> >> ust return grid indices.  This would do the NxM collision check of
> >> particles in grids.
> >>
> >> Writing an octree-aware particle finder would be a good idea.
> >> Necessary, even...
> >>
> >> -Matt
> >>
> >> On Fri, Nov 16, 2012 at 1:07 PM, John ZuHone <jzuhone at gmail.com> wrote:
> >>> I did know about that, but given, say, a million points, would that be
> >>> *fast*? I need to look at what it does I guess.
> >>>
> >>> In FLASH, what'd we'd normally do is start at the top level and traverse
> >>> down the octree until we found the block.
> >>>
> >>> On Nov 16, 2012, at 1:02 PM, Nathan Goldbaum <nathan12343 at gmail.com> wrote:
> >>>
> >>> Hi John,
> >>>
> >>> Yes, you can use pf.h.find_point() to do that.  There's some documentation
> >>> on it here:
> >>> http://yt-project.org/doc/analyzing/low_level_inspection.html#finding-data-at-fixed-points
> >>>
> >>> -Nathan
> >>>
> >>> On Nov 16, 2012, at 10:00 AM, John ZuHone wrote:
> >>>
> >>> Hi all,
> >>>
> >>> Do we have anything in yt right now that, given a set of points, *quickly*
> >>> finds out which grids they belong to?
> >>>
> >>> Best,
> >>>
> >>> John Z
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