[yt-users] Problems with fields

[Matthew Turk]

Hi Cameron,

On Wed, Oct 2, 2013 at 7:06 PM, Cameron Hummels <chummels at gmail.com> wrote:
> Interesting.  When I replace data["GridLevel"] with data.Level, it works in
> cases where I'm using ValidateSpatial(0), but not in cases when
> ValidateSpatial(1) is called.  Even in a simple test case this is true.  So
> for instance this works:
>
> def _testfield(field, data):
>     level = data.Level
>     return data.dds[0]*2.0**level
> add_field("TestField", function=_testfield,
>               validators=[ValidateSpatial(0)])
>
>
> But this does not:
>
> def _testfield(field, data):
>     level = data.Level
>     return data.dds[0]*2.0**level
> add_field("TestField", function=_testfield,
>               validators=[ValidateSpatial(1,["dx"])])
>
> with the traceback pointing to line: "level = data.Level" stating that
> AMRSmoothedCoveringGrid object has no attribute 'Level'.  This is weird
> because the same dataset works for the previous field call so clearly the
> AMRSmoothedCoveringGrid *does* have that attribute.

data.level works, but data.Level does not.

>
> So I guess there is no way around this for 2D datasets, or at least, this 2D
> dataset?  I'm out of ideas here.

This script produces three identical, nice-looking plots for me:

http://paste.yt-project.org/show/3914/

It is based on your notebook.

The problem is almost certainly the combination of the following things:

 * GridLevel (which is ValidateSpatial(0))
 * dx (which as I mentioned previously in IRC usually is used with a
"just_one" call inside a ValidateSpatial field)
 * 2D data
 * Asking for ghost zones

What appears to be going on is that some logic in how the size of the
grids is calculated is causing wraparound along the (false) third
dimension that is added for 2D data, which escalates once you throw in
nested ValidateSpatial fields.  I don't know why you want to use
either VS=0 or VS=1 interchangeably; these are not necessarily meant
to do the same thing.  My suggestion would be that if you want to use
the fields "dx" and "GridLevel" that you instead manually strip off
the z-axis edges of those particular fields if dimensionality < 2.

-Matt