ffc team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Tuesday April 26 2011 08:46:26 Garth N. Wells wrote:
> On 26/04/11 16:39, 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:
> bzr says that you did ;). 

Well, then I did! I just got confused of looking at the patch.

> I'd take credit for it because it adds the
> missing data to the original form.

I bet you do!

Johan

> Garth
> 
> >   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.
> > 
> > Johan
> > 
> >> ?
> >> 
> >> Garth
> >> 
> >>>> 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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