[yt-users] Potential problem with the field_parameters dictionary in SlicePlot (and certainly others)

[Matthew Turk]

Hi Antoine,

This should be fixed in the release put up last night, 3.0.1.  Britton
Smith tracked this down and fixed it.  Apologies for the issue.

-Matt

On Wed, Sep 3, 2014 at 1:40 PM, Antoine Strugarek
<strugarek at astro.umontreal.ca> wrote:
> Thank for your answers, it confirms what I understood.
>
> After digging a bit deeper in the Python and Cython codes, I think I may
> have found another bug that adds up to the problem with ‘_set_center' I was
> mentioning before. In ‘geometric_fields.py’, when computing the geometric
> fields (take _cylindrical_r for instance, but it true for other fields as
> well), the center from the field_parameters dictionary is subtracted from
> the coords. Though, it appears that the coords are obtained from the
> obtain_rvec function defined in geometry_utils.pyx, and in there the center
> (from the field_parameters dictionary as well) is already subtracted. The
> center is hence subtracted twice, which leads to weird behaviours when using
> those geometrical fields. Please advise on what would be the best way to
> cope with this issue, in order to use the already defined geometrical fields
> (cylindrical and spherical).
>
> Antoine
>
>
> Le 2014-09-03 à 13:07 , Nathan Goldbaum <nathan12343 at gmail.com> a écrit :
>
>
>
> On Wed, Sep 3, 2014 at 10:05 AM, Chris Malone <chris.m.malone at gmail.com>
> wrote:
>>
>> Hi Antoine,
>>
>> As you hinted, the field_parameters dictionary is mainly used for derived
>> fields and defaults to the center of the domain.  For a SlicePlot (and
>> others), the keyword variable 'center' is actually what determines where in
>> the domain the slice should be taken - it is completely independent of the
>> field_parameters['center'] value.
>
>
> You can also adjust the plot center using the set_center function that hangs
> off of SlicePlot instances.
>
>>
>>
>> Hope that helps.
>>
>> Chris
>>
>>
>> On Wed, Sep 3, 2014 at 10:45 AM, Antoine Strugarek
>> <strugarek at astro.umontreal.ca> wrote:
>>>
>>> Hi Matthew,
>>>
>>> Thank you for the quick answer. I’m on 3.0 (obtained with
>>> yt.__version__).
>>>
>>> I’m not completely sure how to fix this since I’m discovering the code,
>>> but I’m suspecting something strange there. To my understanding, the
>>> field_parameters dictionary given in argument to SlicePlot should be used
>>> for derived fields only, and the center keyword to specify the location
>>> where the Slice should be taken, right?
>>> Also, if I specify in advance the center (doing ad = ds.all_data() ;
>>> ad.set_field_parameter("center", custom_center)), this new center does not
>>> seem to be used in the SlicePlot to compute, e.g., the cylindrical radius
>>> (in this latter case I try to do a SlicePlot without giving a
>>> field_parameters dictionary in argument).
>>>
>>> Antoine
>>>
>>>
>>> Le 2014-09-03 à 12:27 , Matthew Turk <matthewturk at gmail.com> a écrit :
>>>
>>> > Hi Antoine,
>>> >
>>> > Thanks for reporting this!  Which version of the code are you on?  "yt
>>> > instinfo" should be able to tell you this.
>>> >
>>> > -Matt
>>> >
>>> > On Wed, Sep 3, 2014 at 11:08 AM, Antoine Strugarek
>>> > <strugarek at astro.umontreal.ca> wrote:
>>> >> Hi,
>>> >>
>>> >> I’ve been trying to specify by hand the ‘center’ entry of the
>>> >> dictionary field_parameters to a SlicePlot so that the derived field can
>>> >> make use of another center to compute, e.g., cylindrical coordinates. After
>>> >> tracking why my specified center had no effect, I noticed that the function
>>> >> _set_center is called when a SlicePlot is created, and this function erases
>>> >> any ‘center’ entry in the field_parameters dictionary, putting there the
>>> >> ‘center’ keyword specified as an argument to SlicePlot. It appears to me
>>> >> this should not be the normal behaviour, but I may be misunderstanding
>>> >> something. I would naively suggest not to update the ‘field_parameters’
>>> >> dictionary in the _set_center function, though I’m not completely sure?
>>> >>
>>> >> Thanks in advance for your help and suggestion about this issue!
>>> >>
>>> >> Antoine
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