[yt-dev] fcoords / fwidth in yt-3.0

[Matthew Turk]

Hi all,

Just as a quick word of warning, John ZuHone found this bug:

https://bitbucket.org/yt_analysis/yt/issue/528/cartesian-coordinates-broken-for-flash

The issue in a nutshell is that fcoords is scaling between 0, 1 but
not in a reliable way.  I've looked into it and it seems to me that
the correct solution is the one John identified: remove the scaling
from yt/geometry/cartesian_fields.py .

Looking over the code, I believe most of the frontends are in place to
do exactly that.  I'm going to issue a Pull Request for this bug to
the yt_analysis/yt-3.0 repository shortly, where I remove the scaling
and offsetting from the cartesian_fields.py file.  I have verified
(and fixed) that RAMSES & Gadget are correctly setting fcoords and
fwidth, but I was hoping to get verification from NMSU-ART and ARTIO
before proceeding.

https://bitbucket.org/yt_analysis/yt-3.0/pull-request/21/resetting-cartesian_fieldspy-to-not-apply/diff

The coordinate setting inside grid_patch is correct, so I think once
the octrees are verified, it's ready to go.

I'll update the YTEP to explicitly note that fcoords, fwidth must be
in the domain coordinates.

-Matt

PS Fixing the tests -- not sure what's up with them! -- is on my
agenda for today.