[Yt-dev] boundedness change

[david collins]

I have another, somewhat related question about bounded calculations--
Should one also include the self binding energy of each cell, in
computing the total gravitational binding for an object?

d.

On Sun, Jan 18, 2009 at 9:47 AM, Matthew Turk <matthewturk at gmail.com> wrote:
> (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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