[Yt-dev] boundedness change

Matthew Turk matthewturk at gmail.com
Sun Jan 18 09:47:17 PST 2009


(I responded to Stephen by mistake; I need to fix the reply-to on this
list!  This response is now obsolete.)

Well, one of the problems -- which I addressed with the rather
non-portable CUDA implementation of IsBound -- is that the means of
calculating the potential energy is still n^2.  I think a better means
of calcualting it with the HOP halos is actually to assuming spherical
shells centered on the center of the halo -- even though we all know
halos are not completely spherical, I think we are more likely to have
a good fit to a spherical profile than with hydro clumps.  (Or am I
sorely misled here?)  In that case, what you'd probably want to do is
set up log bins from some minimum radius to the max radius,
caluclating an accumulating sum of mass in those shells, and then
additionally an accumulating sum of kinetic energy.  Then look for
where they cross to find the boundedness.

But, thinking about it, I think this is actually a naive and incorrect
description of what Britton does in the halo profiler when he
calculates the virial radius...  Britton?

(Also, Brian, feel free to chime in about DM halo boundedness.)

-Matt

On Sat, Jan 17, 2009 at 8:59 PM, Stephen Skory <stephenskory at yahoo.com> wrote:
>> I (reluctantly?) agree with Britton that there's an error.  He's going
> to fix it, unless somebody speaks now.  (Else, holding peace forever is
> expected.)
>
> I give up none of my rights!
>
> IsBound interests me. What would be the best way to make this work with HOP haloes? Put a kind of wrapper in the HopGroup class that cuts out a sphere centered on .center_of_mass() with radius .maximum_radius()? I'd prefer to only operate on the DM particles, not the gas mass. Any suggestions?
>
> Thanks!
>
>  _______________________________________________________
> sskory at physics.ucsd.edu           o__  Stephen Skory
> http://physics.ucsd.edu/~sskory/ _.>/ _Graduate Student
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