ffc team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Tuesday April 26 2011 08:48:33 Garth N. Wells wrote:
> On 26/04/11 16:44, 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.

Why is:

  form_data = form.form_data()
  preprocessed_form = form_data._form

so bad? 

> How about something like
> 
>   a.compute_form_data()
> 
> to compute the data, and
> 
>   data = a.form_data()
> 
> to get the FormData. This is like Martin's orginal design, except
> form_data() returns None if the data hasn't been computed.

I think this adds more to the form than is nessesary. 

Johan

> Garth
> 
> >> Where did you add this line?
> > 
> > I change
> > 
> >   preprocessed_form = form
> > 
> > to:
> >   preprocessed_form = form.form_data()._form
> > 
> > Johan
> > 
> >> --
> >> Anders
> >> 
> >>> 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
> >>>>>> 
> >>>>>>>> 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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