ffc team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

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?

--
Anders