ffc team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

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.

> Better would be
> 
>     a.preprocess()
> 
> or
> 
>     a.form_data()

As already mentioned in a previous email, I suggest we only call form_data(). 
This will return the form_data. The preprocessed form is attached to the 
form_data and this is what is passed to the code generator. I am pretty sure 
this is what was there from the beginning.

It is confusing to call:

  form = preprocess(form)

as the preprocessed form was never ment to be doing anything but being passed 
to the code generator, AFAIK.

Johan



> Garth
> 
> > --
> > Anders
> > 
> >> Garth
> >> 
> >>>> Garth
> >>>> 
> >>>>> def preprocess(form, object_names={}, common_cell=None):
> >>>>>     ...
> >>>>>     
> >>>>>     # Check that form is not already preprocessed
> >>>>>     
> >>>>>     if form.form_data() is not None:
> >>>>>         debug("Form is already preprocessed. Not updating form
> >>>>>         data.") return form
> >>>>>     
> >>>>>     ...
> >>>>>     
> >>>>>     # Attach form data to form
> >>>>>     form._form_data = form_data
> >>>>>     
> >>>>>     # Attach preprocessed form to form data
> >>>>>     form_data._form = form
> >>>>> 
> >>>>> And when I look at the blamelist (bzr annotate), it looks like I
> >>>>> added those lines, so I must have come to my senses and added it
> >>>>> back at some point (way back). So in conclusion, calling
> >>>>> preprocess() should not taking any time.
> >>>>> 
> >>>>> What am I missing?
> 
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