[Yt-dev] Field definitions, derived fields, whats-in-a-file and the "deliberate_fields" branch

Matthew Turk matthewturk at gmail.com
Wed Nov 9 14:37:02 PST 2011


Hi David,

On Wed, Nov 9, 2011 at 5:34 PM, david collins <antpuncher at gmail.com> wrote:

> > To be perfectly honest, you were in my list of top one people I thought
> would
> > either love or hate this proposed change.
>
> It wouldn't be so much "hate" as much as "gripe because my
> non-standard code that worked with the 1987 vintage of yt doesn't work
> with the changes you made in 1995." :D  I'm actually really impressed
> that it all went so smoothly, that's a pretty major change with many
> opportunities for bear traps to step in.
>

Well, in fairness, 1995 was a good year for yt.


>
> > Ah!  I think this is what TranslateFunc is designed for.  I think the
> way I
> > envision it working is to choose a canonical name, maybe Bx, and then do:
> > add_enzo_field("Bx", function=NullFunc)
> > add_field("Bx", function=TranslateFunction("MagneticField_C_1"))
>
> Is this now functioning?   I don't quite get the logic behind the
> function calls here, why is Bx itself an "add_enzo_field" but the
> translate is an add_field?
>

That *should* function.  What it does is say, the canonical name is Bx, and
that's the one you'll find in a file (even if you find another) and that
we'll address in yt.  But, just in case, we want it also to return
MagneticField_C_1, if it can't find Bx itself.  So the first goes to the
"known" fields, and the second goes to the "derived" fields.  Does that
make any more sense?

-Matt


>
> Thanks a ton,
> d.
>
> > Thank you.  :)  I have updated the pull request with the new changeset
> where
> > con_args is fixed.
> > Best,
> > Matt
> >
> >>
> >> Thanks a ton!
> >> d.
> >>
> >> Trace for the first bug:
> >>  File "go", line 20, in <module>
> >>    from yt.mods import *
> >>  File "/Users/dccollins/local/src/yt_turk/yt/mods.py", line 44, in
> >> <module>
> >>    from yt.data_objects.api import \
> >>  File "/Users/dccollins/local/src/yt_turk/yt/data_objects/api.py",
> >> line 31, in <module>
> >>    from grid_patch import \
> >>  File
> "/Users/dccollins/local/src/yt_turk/yt/data_objects/grid_patch.py",
> >> line 35, in <module>
> >>    from yt.data_objects.data_containers import YTFieldData
> >>  File
> >> "/Users/dccollins/local/src/yt_turk/yt/data_objects/data_containers.py",
> >> line 3407
> >>    _con_args = {"regions"}
> >>                          ^
> >> SyntaxError: invalid syntax
> >>
> >>
> >>
> >> On Wed, Nov 9, 2011 at 1:25 PM, j s oishi <jsoishi at gmail.com> wrote:
> >> > Hi Matt,
> >> >
> >> > This sounds like a much needed overhaul. However, I'm not quite clear
> >> > on exactly what this will entail, or how it will work once
> >> > implemented. Could you or Casey provide an example of a new field or
> >> > two, demonstrating how these dictionaries, fallbacks, and Null
> >> > functions work? I think this is likely a very simple thing, but I'm
> >> > having trouble visualizing it.
> >> >
> >> > thanks,
> >> >
> >> > j
> >> >
> >> > On Wed, Nov 9, 2011 at 9:05 AM, Matthew Turk <matthewturk at gmail.com>
> >> > wrote:
> >> >> Hi all,
> >> >>
> >> >> Over the last couple months, Casey and I have been working -- on and
> >> >> off! -- on a new branch of the code called "deliberate_fields."  This
> >> >> branch will change, in a substantial but easy-to-update way, how
> >> >> fields are handled in yt.
> >> >>
> >> >> I recognize this email is long.  But if you use non-standard fields,
> a
> >> >> bunch of derived fields, unit modifications, any of that, it may
> >> >> affect you.  So I *please* ask that you read it and, if you like,
> >> >> contribute back to the discussion.
> >> >>
> >> >> This is one of the items I really want to have done for a
> hypothetical
> >> >> 2.3 release.
> >> >>
> >> >> = Background =
> >> >>
> >> >> The way fields work currently was designed a bit haphazardly.  They
> >> >> use FieldInfoContainers, objects which share state and which contain
> >> >> unions of the known derived fields and the known IO-based fields.
>  One
> >> >> of the problems with this is that the only thing that separates a
> >> >> derived field from a known field is that function that generates the
> >> >> field: the IO-based fields all use a lambda which returns None, and
> >> >> the non-IO based fields return actual fields.  This is pretty
> >> >> sub-optimal, and it actually lands us in trouble when (for instance)
> >> >> we have fields wandering around named things like "Thermal_Energy"
> and
> >> >> "ThermalEnergy"; the mechanism by which one is selected and the other
> >> >> not is problematic, and to get around infinite recursion, hacks have
> >> >> had to be applied.
> >> >>
> >> >> As it stands, to find a field, the shared-state "field info" on a
> >> >> parameter file is queried; this then will try to check universal
> >> >> fields.  But because of how the fields are stored, the field info
> >> >> cascade can also operate in reverse.  The big problem is that the
> >> >> field selection mechanism doesn't seem to have a bus factor >= 1.0.
> >> >> And, it has a number of hacks to make it work with conflicting field
> >> >> definitiosn and the like.
> >> >>
> >> >> Unfortunately, layering these hacks on top of each other makes it
> much
> >> >> harder for other codes to be supported; translations are not
> reliable,
> >> >> and sometimes cause too many levels of recursion to be added.
> >> >> Something simpler is necessary.
> >> >>
> >> >> = What this does =
> >> >>
> >> >> Essentially, this creates multi-level, explicit fallbacks.  The field
> >> >> info container, which was a bloated, weird shared state object, is
> now
> >> >> simply a dictionary subclass with a "fallback" option.  When you
> >> >> create them, you can either create it in isolation (with no fallback)
> >> >> or with a fallback.  When you query it, if it does not have a field,
> >> >> it checks its fallback.  There are, additionally, two new functions
> >> >> for IO: the translation function and the null function.  The first is
> >> >> to translate, for instance, "density" to "Density" and the second is
> >> >> to indicate that a field is expected to be found in an output from
> the
> >> >> simulation code.
> >> >>
> >> >> There are now affiliated with each simulation code two field info
> >> >> objects: the "known" fields, which may appear in files, and the
> >> >> non-known (i.e., code-specific derived) fields.  These live as the
> >> >> attributes _fieldinfo_fallback and _fieldinfo_known on the
> >> >> StaticOutput sublcass corresponding to a simulation code.  When the
> >> >> Hierarchy (not static output) is instantiated, the first step is to
> >> >> create a new field_info object.  This has, as a fallback, the
> >> >> _fieldinfo_fallback, which itself has as a fallback the
> >> >> universally-known derived fields.  The hierarchy then queries the
> >> >> output file for which fields are available.  This process then looks
> >> >> for a corresponding field in fieldinfo_known, and if it finds it, it
> >> >> adds it to the field_info object, *overriding* any possible derived
> >> >> fields.  (In this manner, for instance, yt will not recalculate a
> >> >> "CoolingTime" field if one exists in the output.)
> >> >>
> >> >> = What it aims to do in the future =
> >> >>
> >> >> This will be utilized in three main ways:
> >> >>
> >> >> 1) Making it more clear which fields belong to which code, and which
> >> >> come from disk and which are derived
> >> >> 2) Help move IO into fields, to optimize for geometries and data
> >> >> containers
> >> >> 3) Make units more clear and specific
> >> >> 4) This is all designed around better supporting the GDF.
> >> >>
> >> >> = Where from here? =
> >> >>
> >> >> It would be hugely beneficial if you could test this and report back.
> >> >> I have created a pull request:
> >> >>
> >> >>
> >> >>
> https://bitbucket.org/yt_analysis/yt/pull-request/27/field-overhaul-to-utilize-explicit
> >> >>
> >> >> This is by no means a settled matter; I think we need to have testing
> >> >> on this, buy-in from developers and users, and to make sure that old
> >> >> code doesn't beak.  The test cases all pass for me for Enzo.
> >> >>
> >> >> Before this can be merged, I would hope we can get some testing from:
> >> >>
> >> >>  * Enzo
> >> >>  * Nyx
> >> >>  * FLASH
> >> >>  * Orion
> >> >>
> >> >> and any other codes that can hear me.
> >> >>
> >> >> Thanks very much for your time; please let me know if you have any
> >> >> questions, concerns, jokes, comments, improvements, CDs of your band,
> >> >> suggestions, and so on.  For this major of a change I'd like to keep
> >> >> discussion on list, so the record of this is a bit more prominent.
> >> >>
> >> >> Best,
> >> >>
> >> >> Matt
> >> >> _______________________________________________
> >> >> Yt-dev mailing list
> >> >> Yt-dev at lists.spacepope.org
> >> >> http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org
> >> >>
> >> > _______________________________________________
> >> > Yt-dev mailing list
> >> > Yt-dev at lists.spacepope.org
> >> > http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org
> >> >
> >>
> >>
> >>
> >> --
> >> Sent from my computer.
> >> _______________________________________________
> >> Yt-dev mailing list
> >> Yt-dev at lists.spacepope.org
> >> http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org
> >
> >
> > _______________________________________________
> > Yt-dev mailing list
> > Yt-dev at lists.spacepope.org
> > http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org
> >
> >
>
>
>
> --
> Sent from my computer.
> _______________________________________________
> Yt-dev mailing list
> Yt-dev at lists.spacepope.org
> http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.spacepope.org/pipermail/yt-dev-spacepope.org/attachments/20111109/63e9d550/attachment.htm>


More information about the yt-dev mailing list