[Yt-dev] yt fof question

[Britton Smith]

Ok, call off the troops.  It looks like we made a bit of a mistake over
here.  After checking two particles lists made on the same data with yt FOF
and inline FOF, we've found that the particle lists are actually nearly
identical.  The only difference is that yt FOF is completely missing 4 small
(~600 particles for a 128^3 sim) halos that are found by the inline FOF.  We
still don't know what is the cause of this.  Making a projection of the
position where the inline FOF finds one of these missing halos, it looks
like there might be something there, but it's pretty marginal given the size
of the halo.

Anyway, I would say it's safe to return to Defcon 5.  I apologize for
causing a fuss and wasting people's time.  We should have looked a little
more carefully at the issue.  We're still working out some issues over here,
but I don't think they involve the halo finders.

Sorry again for the inconvenience.

Britton

On Thu, Oct 15, 2009 at 10:46 AM, John Wise <jwise at astro.princeton.edu>wrote:

> Hey Britton and Stephen,
>
> Unless it was already obvious, I just wanted to chime in that the inline
> FOF uses the same particles IDs in the main calculations of enzo.
>
> John
>
> On 15 Oct 2009, at 12:43, Britton Smith wrote:
>
> Stephen,
>
> It looks like if I take any random particle in a halo made with yt FOF,
> it's in a completely different halo in inline FOF, or not in any halo at
> all.  Michele is checking this out right now, but it basically looks like
> the particle lists for the same halo found with the two different methods
> are completely different.
>
> Britton
>
> On Thu, Oct 15, 2009 at 10:22 AM, Stephen Skory <stephenskory at yahoo.com>wrote:
>
>> Britton,
>>
>> >I'll check the yt FOF IDs against Enzo right now.  The halo output of the
>> code seems just fine, so if there's a bug, it's minor.  I'll let you know
>> what I find.
>>
>> I remembered that the kD tree yt FOF uses is a bit inaccurate, and that
>> could be a source of difference between the two sets of FOF haloes. But you
>> said the differences were huge, and the kD inaccuracy should give only small
>> differences, especially in FOF. Just a thought.
>>
>>  _______________________________________________________
>> sskory at physics.ucsd.edu           o__  Stephen Skory
>> http://physics.ucsd.edu/~sskory/ <http://physics.ucsd.edu/%7Esskory/>_.>/ _Graduate Student
>> ________________________________(_)_\(_)_______________
>>
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