[yt-users] Profiles, root grid

[David Collins]

> In reference to the __getitem__ issue, it can be challenging to debug
> this sort of thing remotely without the line that causes the error and
> a traceback.

Sorry about that.  I wanted to do a little more digging before sending
out an actual request for help. (good for my yt knowledge) Since I
have a workaround, this is now not very high priority, but it seems
like a bug so I thought I'd see if I could fix it.  I fixed one bug,
but then got stuck:

The problem I had was trying to do a profile on a covering grid using
the lazy reader, but the real problem comes from a derived quantity on
a covering grid with the lazy_reader=True, as in

cg = pf.h.covering_grid(0,left,resolution)
cg.quantities['Extrema']('Density')

Initially this throws a key error, "can't find key 'D'".  I sorted
this one out, but then got stuck.  Both problems stem from the same
_get_data_from_grid call on the covering grid.

When the derived quantity __call__ grabs data from the data source, it
does it (eventually) through a call to
AMRCoveringGridBase._get_data_from_grid (data_containers lin 3302),
which has the line:

g_fields = [grid[field] for field in fields]

which needs an ensure_list around fields so it doesn't try to iterate
over a string (which is why they key error on 'D').  I'm comfortable
checking in this change.

My next question is the general behavior of this function, which I'm
not comfortable changing:  Instead of
AMRCoveringGridBase._get_data_from_grid returning a data object, as
the name would imply, it returns an integer.  Is this what's supposed
to happen?  The string also causes problems with the derived quantity,
since several places expect an array.  This is the code in question:

    def _get_data_from_grid(self, grid, fields):
        ll = int(grid.Level == self.level)
        ref_ratio = self.pf.refine_by**(self.level - grid.Level)
        g_fields = [grid[field] for field in ensure_list(fields)]
        c_fields = [self[field] for field in ensure_list(fields)]
        count = FillRegion(ref_ratio,
            grid.get_global_startindex(), self.global_startindex,
            c_fields, g_fields,
            self.ActiveDimensions, grid.ActiveDimensions,
            grid.child_mask, self.domain_width, ll, 0)
        return count

The full test and trace are here, wherein you can see the error that
data[field] has returned a number, not a numpy array.

>>> cg = b.h.covering_grid(0,[0.0]*3,[256]*3)
>>> cg.quantities['Extrema']('Density')

Parsing Hierarchy100%
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Time: 00:00:00
Warning: divide by zero encountered in divide
Warning: divide by zero encountered in divide
Searching grids for values 100%
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Time: 00:00:01
Traceback (most recent call last):
  File "tmp.py", line 18, in <module>
    cg.quantities['Extrema']('Density')
  File "/Users/dccollins/local/src/yt-hg/yt/data_objects/derived_quantities.py",
line 92, in __call__
    return self._call_func_lazy(args, kwargs)
  File "/Users/dccollins/local/src/yt-hg/yt/data_objects/derived_quantities.py",
line 100, in _call_func_lazy
    rv = self.func(GridChildMaskWrapper(g, self._data_source), *args, **kwargs)
  File "/Users/dccollins/local/src/yt-hg/yt/data_objects/derived_quantities.py",
line 544, in _Extrema
    if data[field].size < 1:
AttributeError: 'int' object has no attribute 'size'

Thanks!
d.

>
> -Matt
>
> On Mon, May 9, 2011 at 10:24 AM, David Collins
> <dcollins at physics.ucsd.edu> wrote:
>> Hey, Matt--
>>
>> I found that if I do "lazy_reader = False" the covering grid works
>> fine.  It looks like somewhere the field string in one of the
>> __getitem__  calls is being treated like a list.
>>
>> I'm interested in using this with some derivative quantities, can I
>> just send 'DivV' to the grid collection in your example, or will I
>> have to let it know that it should grab ghost zones?
>>
>> d.
>>
>> On Mon, May 9, 2011 at 10:57 AM, Matthew Turk <matthewturk at gmail.com> wrote:
>>> Hi David,
>>>
>>> Try a grid_collection:
>>>
>>> gc = pf.h.grid_collection([0.5,0.5,0.5], [pf.h.grids[0]])
>>>
>>> Note that it still requires a 'center'.  Also, this object is not
>>> supposed to do any child masking, so if you find that it does, let me
>>> know.
>>>
>>> -Matt
>>>
>>> On Mon, May 9, 2011 at 9:43 AM, david collins <antpuncher at gmail.com> wrote:
>>>> Hi there--
>>>>
>>>> I'd like to add a profile object using only the root grid.  I
>>>> typically do something like this:
>>>>
>>>> pc.add_profile_object(region,fields, weight=weight)
>>>>
>>>> Is there a way to restrict this to only root grid tiles?  I've tried
>>>> using a covering grid, but that's throwing some key error (that I'm
>>>> looking into presently, I'll have more info if/as I sort it out)
>>>>
>>>> Thanks,
>>>> d.
>>>>
>>>> --
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