[yt-dev] ipython-physics

[Anthony Scopatz]

I am +1 for adding sympy.

On Tue, Oct 23, 2012 at 9:55 AM, Matthew Turk <matthewturk at gmail.com> wrote:

> Hi all,
>
> Sorry for letting this drop.
>
> My feeling is that we should definitely go with dimensionful (Casey's
> project), and add SymPy to the stack.  It seems likely that the
> emerging SciPy stack will include SymPy as a component, and
> furthermore it's pure python, so it should not be terribly difficult
> to include in that respect.
>
> Having a coherent unit stack is crucial.  Right now we have the
> really, really terrible (and I take full blame for this) overloading
> of parameter files like dictionaries.  As an example, here's how Enzo
> would work:
>
> pf["time"]
> pf["InitialTime"]
> pf["kpc"]
> pf["HydroMethod"]
> pf["seconds"]
> pf["Density"]
>
> All of these do different things.  And, on the backend, they query
> different dictionaries -- units, conversion_factors, and parameters.
> This is not okay!  We have:
>
> pf.current_time
>
> but this is given in code units for some reason for most codes.
>
> I think we should move to a system where when querying, the person
> doing the querying needs to explicitly state what they want.  And all
> the unit conversion stuff (time, length, fluid, etc) needs to be
> handled by a separate process -- and my preference would be that it
> would be handled by dimensionful.  I think that can come in at a
> higher level than the conversion from on-disk to CGS, but it should
> come in somewhere.
>
> I would absolutely love to rip out all of the dictionary-access for
> parameters this instant -- moving to tuples of (value, unit) was the
> first step, to get away from value/pf[unit].  But we can't do this
> just yet, and it needs to happen at a 3.0 break.
>
> What does everyone think?  Can we do a [+-][01] on SymPy +
> Dimensionful, or do we need more info?
>
> -Matt
>
> On Sat, Oct 6, 2012 at 12:59 AM, Anthony Scopatz <scopatz at gmail.com>
> wrote:
> > Hi Mike,
> >
> > ipython-physics looks like a good, relatively simple solution.  I would
> > assume that we would use this *instead* of sympy to prevent having to add
> > yet-another-dependency and end up packaging this right with yt.  (ip-p
> seems
> > to be unlicensed yet 'placed in the public domain', which is weird since
> the
> > public domain is not a legal construct everywhere.  We would need to ask
> > them about that before including in yt.)
> >
> > That said, I think a sympy solution would end up being more powerful
> > ultimately.  Additionally, ip-p definitely needs some clean up before
> > inclusion.  At quick glance they seems to use camel case for some
> functions,
> > their main class NumberDict subclasses from dict (huge no-no,
> > collections.MutableMapping people!), all of the _addUnit() calls at the
> end
> > of the file should be hard coded into _unit_table (or a mapped call),
> they
> > seem to be definitely using eval() wrong by not having an empty globals
> dict
> > which captures builtins, and the unit comments never seem to be used (so
> why
> > have them?).  And they have no tests!
> >
> > So I would be in favor a rewrite of ip-p, but sympy would be better ;)
> >
> > Be Well
> > Anthony
> >
> > On Fri, Oct 5, 2012 at 7:24 PM, Michael Kuhlen <mqk at astro.berkeley.edu>
> > wrote:
> >>
> >> Hi yt gang
> >>
> >> Just had a little chat with Matt, and he suggested I bring up
> >> ipython-physics for discussion. Sounds like unit handling is an issue
> that
> >> needs to be addressed in yt. I've found ipython-physics to be pretty
> neat
> >> and quite usable. Maybe this is something worth tying into yt? Matt also
> >> mentioned that Casey had written a sympy-based library for handling
> units;
> >> how does it compare to what ipython-physics does?
> >>
> >> Mike
> >>
> >> --
> >> *********************************************************************
> >> *                                                                   *
> >> *  Dr. Michael Kuhlen              Theoretical Astrophysics Center  *
> >> *  email: mqk at astro.berkeley.edu   UC Berkeley                      *
> >> *  cell phone: (831) 588-1468      B-116 Hearst Field Annex # 3411  *
> >> *  skype username: mikekuhlen      Berkeley, CA 94720               *
> >> *                                                                   *
> >> *********************************************************************
> >>
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