ffc team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

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. This means that 
we need to return form_data from preprocess and maybe change its name to 
compute_form_data.

Johan

> --
> Anders