ffc team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Tue, Apr 26, 2011 at 09:24:02AM -0700, Johan Hake wrote:
> On Tuesday April 26 2011 09:18:15 Garth N. Wells wrote:
> > On 26/04/11 17:16, Anders Logg wrote:
> > > On Tue, Apr 26, 2011 at 06:12:26PM +0200, Martin Sandve Alnæs wrote:
> > >> On 26 April 2011 18:10, Johan Hake <johan.hake@xxxxxxxxx> wrote:
> > >>     On Tuesday April 26 2011 09:01:35 Anders Logg wrote:
> > >>     > On Tue, Apr 26, 2011 at 08:44:24AM -0700, Johan Hake wrote:
> > >>     > > On Tuesday April 26 2011 08:42:32 Anders Logg wrote:
> > >>     > > > On Tue, Apr 26, 2011 at 08:39:30AM -0700, Johan Hake wrote:
> > >>     > > > > On Tuesday April 26 2011 08:33:11 Garth N. Wells wrote:
> > >>     > > > > > On 26/04/11 16:31, Johan Hake wrote:
> > >>     > > > > > > On Tuesday April 26 2011 08:16:29 Garth N. Wells wrote:
> > >>     > > > > > >> On 26/04/11 16:07, Anders Logg wrote:
> > >>     > > > > > >>> On Tue, Apr 26, 2011 at 03:59:52PM +0100, Garth N.
> > >>     > > > > > >>> Wells
> > >>
> > >>     wrote:
> > >>     > > > > > >>>> On 26/04/11 15:55, Anders Logg wrote:
> > >>     > > > > > >>>>> On Tue, Apr 26, 2011 at 03:45:22PM +0100, Garth N.
> > >>     > > > > > >>>>> Wells
> > >>
> > >>     wrote:
> > >>     > > > > > >>>>>> On 26/04/11 13:51, Anders Logg wrote:
> > >>     > > > > > >>>>>>> On Tue, Apr 26, 2011 at 02:00:50PM +0200, Anders
> > >>     > > > > > >>>>>>> Logg
> > >>
> > >>     wrote:
> > >>     > > > > > >>>>>>>> It feels good that you trust me enough to handle
> > >>     > > > > > >>>>>>>> it. ;-)
> > >>     > > > > > >>>>>>>>
> > >>     > > > > > >>>>>>>> Will add it sometime this afternoon and then we
> > >>     > > > > > >>>>>>>> can revisit the JIT compiler caching.
> > >>     > > > > > >>>>>>>
> > >>     > > > > > >>>>>>> I'm getting confused here... Looking at
> > >>     > > > > > >>>>>>> preprocess.py in UFL, I see
> > >>     > > > > > >
> > >>     > > > > > > this:
> > >>     > > > > > >>>>>> It is confusing. Does the function 'preprocess' do
> > >>
> > >>     anything
> > >>
> > >>     > > > > > >>>>>> that the old FormData class didn't? It would be
> > >>     > > > > > >>>>>> easier to follow if Form just had a member
> > >>     > > > > > >>>>>> function form_data() that computes and stores data
> > >>     > > > > > >>>>>> (like it used to), or if Form had a 'preprocess'
> > >>     > > > > > >>>>>> function. Having the function preprocess return a
> > >>     > > > > > >>>>>> new form is really confusing.
> > >>     > > > > > >>>>>
> > >>     > > > > > >>>>> I don't find that particularly confusing. It's the
> > >>     > > > > > >>>>> same as
> > >>     > > > > > >>>>>
> > >>     > > > > > >>>>>   refined_mesh = refine(mesh)
> > >>     > > > > > >>>>
> > >>     > > > > > >>>> Which is the whole problem. By creating a new object,
> > >>
> > >>     FormData
> > >>
> > >>     > > > > > >>>> is thrown away. The preprocessing should just compute
> > >>     > > > > > >>>> some more data, just like we *don't* do
> > >>     > > > > > >>>>
> > >>     > > > > > >>>>   initialised_mesh = mesh.init(0)
> > >>     > > > > > >>>>
> > >>     > > > > > >>>> What was wrong with Martin's original design that
> > >>
> > >>     necessitated
> > >>
> > >>     > > > > > >>>> the change?
> > >>     > > > > > >>>
> > >>     > > > > > >>> As I explained, I thought it was better to have an
> > >>     > > > > > >>> explicit call to preprocess since that makes it clear
> > >>     > > > > > >>> that one makes a call to a function which may take
> > >>     > > > > > >>> some time to execute (instead of just calling a
> > >>     > > > > > >>> member function which seems to
> > >>
> > >>     just
> > >>
> > >>     > > > > > >>> return some data).
> > >>     > > > > > >>>
> > >>     > > > > > >>> But as I say above: I added the caching back at some
> > >>     > > > > > >>> point (maybe even the day after I removed it 2 years
> > >>     > > > > > >>> ago) so we don't need to discuss why I removed it (as
> > >>     > > > > > >>> I realized myself
> > >>
> > >>     I
> > >>
> > >>     > > > > > >>> shouldn't have removed it and added it back a long
> > >>     > > > > > >>> time ago).
> > >>     > > > > > >>>
> > >>     > > > > > >>> What has me confused now is that the caching seems to
> > >>     > > > > > >>> be in place but we still need the extra caching in
> > >>     > > > > > >>> FFC/DOLFIN and I don't see why.
> > >>     > > > > > >>
> > >>     > > > > > >> Because preprocess returns a new form, e.g. define a
> > >>     > > > > > >> form
> > >>     > > > > > >>
> > >>     > > > > > >>   a = u*v*dx
> > >>     > > > > > >>   jit(a)
> > >>     > > > > > >>
> > >>     > > > > > >> Inside jit,
> > >>     > > > > > >>
> > >>     > > > > > >>    a.form_data() is None:
> > >>     > > > > > >>        b = preprocess(a) # b now has data attached, but
> > >>     > > > > > >>        a doesn't
> > >>     > > > > > >>
> > >>     > > > > > >>    else:
> > >>     > > > > > >>        b = a
> > >>     > > > > > >>
> > >>     > > > > > >> Now 'b' has been preprocessed, and has form data
> > >>     > > > > > >> attached, but 'a' doesn't. Calling 'jit(a)' again, the
> > >>     > > > > > >> code will never enter the 'else' part of the clause
> > >>     > > > > > >> because 'a' never gets any form data. Johan has added
> > >>     > > > > > >> some code FFC that attaches the form
> > >>
> > >>     data
> > >>
> > >>     > > > > > >> of 'b' to 'a', but it is a bit clumsy.
> > >>     > > > > > >
> > >>     > > > > > > No, it was already attached. I just made ffc use it.
> > >>     > > > > >
> > >>     > > > > > Didn't you add the line
> > >>     > > > > >
> > >>     > > > > >     form._form_data = preprocessed_form.form_data()
> > >>     > > > >
> > >>     > > > > No, I added:
> > >>     > > > >   preprocessed_form = form.form_data()._form
> > >>     > > > >
> > >>     > > > > I think the thing here is that form_data has always had a
> > >>     > > > > preprocessed form. Someone (lets not point fingers!) thought
> > >>     > > > > that was too much magic and added an
> > >>     > > > >
> > >>     > > > > explicit need to call:
> > >>     > > > >   form = preprocess(form)
> > >>     > > > >
> > >>     > > > > in jit_compiler(). This made the design more complicated and
> > >>     > > > > also introduced a cirucular dependency, as the return
> > >>     > > > > preprocessed form need to know of its form_data, but the
> > >>     > > > > form_data already had a reference to the preprocessed form.
> > >>     > > > > The latter is what I used in
> > >>
> > >>     the
> > >>
> > >>     > > > > one line I altered.
> > >>     > > >
> > >>     > > > No, it made the design cleaner since it makes clear something
> > >>     > > > needs
> > >>
> > >>     to
> > >>
> > >>     > > > happen to get the metadata: a call to preprocess.
> > >>     > > >
> > >>     > > > Where did you add this line?
> > >>     > >
> > >>     > > I change
> > >>     > >
> > >>     > >   preprocessed_form = form
> > >>     > >
> > >>     > > to:
> > >>     > >   preprocessed_form = form.form_data()._form
> > >>     >
> > >>     > Yes, but where?
> > >>     >
> > >>     > I've fixed the bug now in preprocess.py (attaching to both forms).
> > >>     > Does that help?
> > >>
> > >>     In ffc.jit_form.
> > >>
> > >>     Your fix wont fix the circular dependency.
> > >>
> > >>     We also need to remove form_data from the preprocessed form.
> > >>
> > >> Or just use a weakref.
> > >>
> > >>     This means that
> > >>     we need to return form_data from preprocess and maybe change its
> > >>     name to compute_form_data.
> > >>
> > >>     Johan
> > >
> > > Why is the circular dependency a problem? Anyway, I'm thinking now the
> > > cleanest design would be
> > >
> > >   form.compute_form_data()
> > >   form_data = form.form_data()
> > >   preprocessed_form = form_data.preprocessed_form
> > >
> > > Here, the preprocessed_form would not store form_data.
> >
> > Agree.
>
> Go for it! We would then also avoid problems with ciruclar dep.

Great! Will fix soon.

> Still think form.compute_form_data() line is superflous ;)

I foresee we will have another long discussion in a year or two and we
will then end up removing compute_form_data... :-)

--
Anders