So we need something akin to adding particle filters?  Define the field_parameter and then add the field_parameter?  That seems reasonable to me.

On Thu, Oct 2, 2014 at 7:42 AM, Matthew Turk <matthewturk@gmail.com> wrote:
On Thu, Oct 2, 2014 at 9:41 AM, Cameron Hummels <chummels@gmail.com> wrote:
> I like the option of just adding a "dimension" argument to when you
> declare/add a field_parameter.  That retains the freedom of making your own
> field_parameters, but seems to fix this dimensional problem.

We'd also need to add a step where they are added or declared that
isn't inside userspace code.

>
> Cameron
>
> On Thu, Oct 2, 2014 at 5:36 AM, Matthew Turk <matthewturk@gmail.com> wrote:
>>
>> Hi Hilary,
>>
>> Maybe we ought to have a registry of known field parameters,
>> affiliated with dimensions.  A while back I looked at the known ones,
>> and there were not many in use.  It might be relatively
>> straightforward to set up a simple registry.  My concern is then that
>> individuals wanting to define their own are going to run into an issue
>> of the behavior changing, not knowing how to fix it, and so on.
>>
>> Alternately, we could use a default parameter in those failing fields.
>> Or, we could add an argument to the add_field call of the dimensions
>> of the field parameter.
>>
>> -Matt
>>
>> On Wed, Oct 1, 2014 at 3:22 PM, Hilary Egan <hilaryye@gmail.com> wrote:
>> > Hi all,
>> >
>> > I've encountered a bug with this example in the docs of getting/setting
>> > field parameters of a dataset for use in a derived field. The example
>> > works
>> > fine for known yt field parameters like bulk_velocity, but if you change
>> > every instance of "bulk_velocity" to "my_bulk_velocity" (sample script),
>> > then it breaks with this error.
>> >
>> > It seems as though this breaks because `has_field_parameter` always
>> > returns
>> > True, and there is no way to know ahead of time what units a
>> > user-defined
>> > field parameter will take, so the mock field data can't be set up
>> > correctly.
>> > Nathan suggested via IRC that this might necessitate creating a way to
>> > register user-defined field parameters, but it's probably worth
>> > brain-storming about if anyone else has any other suggestions!
>> >
>> > -Hilary
>> >
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>> >
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>
>
>
> --
> Cameron Hummels
> Postdoctoral Researcher
> Steward Observatory
> University of Arizona
> http://chummels.org
>
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--
Cameron Hummels
Postdoctoral Researcher
Steward Observatory
University of Arizona
http://chummels.org