[yt-dev] yt & Enzo w. Zeus

[Elizabeth Tasker]

I meant to add that I ran the script below on an isolated galaxy disc
with radius 12 kpc, smallest cell size of 8pc and a steep velocity
gradient in the radial direction. With a small sphere radius around 20
pc, then the difference between zeus-adjusted and non-zeus is not at
all bad:

x: 0.966613809275
y: 0.9929356881
z: 0.611797194496

(z-direction is not well resolved).

But scale that up to 1 kpc and it's more dramatic:

x: 0.51838881789
y: 1.57845583686
z: 4.74831176192

Elizabeth

On 24 February 2012 20:00, Elizabeth Tasker
<tasker at astro1.sci.hokudai.ac.jp> wrote:
> 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