[yt-dev] yt & Enzo w. Zeus

[Elizabeth Tasker]

Hi,

I wanted to discuss a possibly more consistent way of dealing with
velocities in yt when analysing a simulation with Enzo's Zeus hydro
scheme (HydroMethod = 2).

Because Zeus' velocities are face-centred, not cell centred, there is
a half-cell off-set that the routines in yt sometimes allow for and
sometimes do not. For instance, the DivV does allow for Zeus' off-set
but the calculation of the SpecificAngularMomentum does not. I often
hit this problem when examining objects with yt. Either I have to
pretend Zeus has cell-centred velocities or write a new routine which
is a nuisance.

I was wondering if we could introduce a universal field that
cell-centred Zeus' velocities. I think it would look like this:

http://paste.yt-project.org/show/2192/

But, I have three questions:

(1) Does the scheme (using the slice(None, -1, None) for arrays) work
if "data" is not a continuous region, e.g. a collection of cells made
through extract_region?

(2) Could this be implemented such that, if you were using Zeus, the
universal fields "x-velocity", "y-velocity" and "z-velocity" were
over-written by these new definitions? (If that was done throughout
yt, then other references to Zeus in routines like DivV would have to
be removed. This is probably still easier than adding in new ones
everywhere).

(3) Is it possible for me to do that on my own local version? e.g. can
I put field definitions in a folder to over-write the default yt ones?

Thanks~

Elizabeth