[Yt-dev] disk analysis

[Matthew Turk]

Hi guys,

After some chats with Jeff this morning, and following up on those
with a discussion with Ji-hoon Kim, I'd like to bring up the idea of
disk analysis.  I will summarize first the current status and then
where I think it can be taken over the next week or so.

Currently, disks can be analyzed by calculating the angular momentum
vector over some known sphere, then using that to bin quantities by
height/radius.  Cutting planes (thin) can be made with the code,
AMRCylinders (without any *new* or *tranformed* spatial information)
can be constructed and binned.  Projected cutting planes can be made,
but it is kind of slow and a recipe has to be used rather than a
simple, provided API.  Inertial tensor fields are available, but have
to be manually diagonalized.

In short, there's a lot that can be done, but it's not terribly easy.

I'd like to see this expand to be handled through a single interface,
similar to the halo profiler, called the DiskAnalyzer.  This would
take a sphere, or some region, step out over spherical shells and at
each shell identify the declination from an abitrary vector (possibly
bulk L_vec of the data source as a whole) of the average density.  It
would calculate the scale height for the density in that spherical
shell.  Once this is done, the scale height as a function of radius
will be had, as well as the alignment of the disk as a function of
declination from the central (arbitrary) vector.

Once this information is collected, we need to construct a disk
'image.'  As I see it, this can be aligned with the angle of maximum
density, as calculated by binning by declination from our arbitrary
vector.  However, one could also imagine aligning it with the angular
momentum vector (commonly done now) or the diagonalized inertial
tensor.  I'm not sure which is the right one to do.  At this point,
profiles as a function of scale height and radius are possible or
already completed, and we have a disk image.  Toomre Q can be
calculated and we should have complete set of diagnostics for the
disk.

Can anyone think of what else should be done?  And are there any flaws
in my proposal?  (What about the vector for defining the projected
image -- which is the best of the three?)

Thanks guys!

-Matt

PS I'm getting half of my wisdom removed on Tuesday, so I will be on
painkillers a bit this week, so I will be in and out of email contact.