[Yt-dev] boundedness change

[Matthew Turk]

It's unclear to me that we should.  If we did, it would be a simple
addition to the total potential, rather than anything that needed to
be calculated through a C function.  My brain is blanking right now,
but what is the self-binding energy of a rectangular prism of given
mass, assuming hte mass is distributed evenly?

On Sun, Jan 18, 2009 at 11:38 AM, david collins <antpuncher at gmail.com> wrote:
> 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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