[yt-dev] Field naming proposal

Nathan Goldbaum nathan12343 at gmail.com
Tue Dec 23 12:23:05 PST 2014


On Tue, Dec 23, 2014 at 11:47 AM, Michael Zingale <
michael.zingale at stonybrook.edu> wrote:

> Matt had a proposal to support general grids, and somewhere inbetween that
> and what yt does now are logical Cartesian curvilinear / quadralaterial
> grids (some people use eta and xi for the coordinate names in 2-d for
> these).  Should those types of grids be address in the field naming
> proposal or Matt's unstructured proposal (technically, these are
> structured, but ...)
>

I think this is unrelated (but Matt please feel free to jump in if you
think this field naming discussion has any bearing on support for
unstructured meshes).

The proposal establishes a standard naming convention for vector fields in
curvilinear coordinates. If people want to use alternate naming
conventions, perhaps it's enough that they can create new alias fields with
their preferred names?  I'm not sure how far down the road of support for
alternative curvilinear naming conventions we need to build in to yt
itself, since that will easily get complicated and confusing.

Fields exist at a high conceptual layer in yt where ideally a user doesn't
need to know anything about the underlying discretization.  When I ask for
the radial coordinate of the of the gas velocity vector for a set of cells,
I don't necessarily care how those cells are discretized.

Do you have am example where the proposed field naming system would be
awkward to work with for some data that we would like to support in the
future?

On Tue, Dec 23, 2014 at 11:54 AM, Michael Zingale <
michael.zingale at stonybrook.edu> wrote:

> perhaps off topic for this, but should yt know about the type of
> discretization for the grid -- i.e. finite-difference vs. finite-volume,
> and should that be indicated in the field name somehow?  The only place I
> see this really coming into play is in creating derived fields -- at the
> moment everything is second-order accurate for a finite-volume code, but if
> someone has a higher-order code they might care about the accuracy that the
> conversions are done to, and perhaps yt should know about the
> discretization.
>
>
I'm not sure whether this should show up in the field names.  Can you
sketch out an example where it would be useful to know the underlying
discretization?

Are you thinking of fields like velocity divergence, where we need to use a
stencil to compute the derived field? If that's the case, I think that
should be implemented using multiple dispatch for python field
implementation functions.  In this approach, the implementation for a field
gets determined at runtime based on the underlying data format.  We do
something similar where we swap out definitions for the energy fields for
codes that conserve either total energy or internal energy.


>
> On Tue, Dec 23, 2014 at 2:01 PM, Nathan Goldbaum <nathan12343 at gmail.com>
> wrote:
>
>> Hi all,
>>
>> I've just issued a pull request that bears some developer discussion.
>>
>> Right now yt is a bit of a wild west in terms of the field naming
>> convention for fields that reference a coordinate system.  See for example,
>> see issue 947:
>>
>>
>> https://bitbucket.org/yt_analysis/yt/issue/947/consistent-field-naming-for-spherical-and
>>
>> I'd like to propose a naming convention for fields that reference a
>> coordinate system.  Gas and particle fields should be of the form:
>>
>> (field_type, "<particle?>_<vector_field_name>_<coordinate>")
>>
>> while index fields for coordinates should be of the form:
>>
>> ("index", "<coordinate>")
>>
>> This fits within our existing field naming convention for cartesian
>> coordinates, e.g.:
>>
>> ("gas", "velocity_x")
>> (ptype, "particle_velocity_y")
>>
>> as well as our convention for index coordinate fields, e.g.:
>>
>> ("index", "x")
>> ("index", "spherical_theta")
>>
>> This means that index fields do not need to explicitly reference
>> themselves as positions.  So we *won't* have field names like:
>>
>> ("index", "position_x")
>>
>> I don't like the above construction because it's a bit redundant ("index"
>> implies that we are talking about a position or something similar).
>>
>> Some existing field names will need to be changed to fit this.  In
>> particular, some of the index fields will need to be renamed to be more
>> verbose ("index", "spherical_r") becomes ("index", "spherical_radius") and
>> (ptype, "particle_spherical_position_radius") becomes (ptype,
>> "particle_position_spherical_radius").
>>
>> Wherever an existing field name needs to change, I propose we mark the
>> existing field name for deprecation, stub it out, and make it an alias for
>> the field with the new field name.  In a future release, we can then remove
>> the deprecated fields.
>>
>> I've implemented this for the particle fields (for the most part) in PR
>> 1378:
>>
>> https://bitbucket.org/yt_analysis/yt/pull-request/1378
>>
>> I'm happy to update the field naming YTEP if this proposed field naming
>> scheme gets approval in this thread.
>>
>> What do you all think?  Question, concerns?
>>
>> -Nathan
>>
>>
>>
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>>
>>
>
>
> --
> Michael Zingale
> Associate Professor
>
> Dept. of Physics & Astronomy • Stony Brook University • Stony Brook, NY
> 11794-3800
> *phone*:  631-632-8225
> *e-mail*: Michael.Zingale at stonybrook.edu
> *web*: http://www.astro.sunysb.edu/mzingale
>
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