ufl team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

On Mon, Apr 20, 2009 at 1:27 PM, Anders Logg <logg@xxxxxxxxx> wrote:
> On Mon, Apr 20, 2009 at 01:21:07PM +0200, Martin Sandve Alnæs wrote:
>> Yes, I agree that the data flow can be confusing,
>> and I've intended to discuss it for a while.
>> But there's so much to do and so little time, we
>> can't do any major restructuring right now anyway...
>>
>> In SFC, I do this as the first thing:
>>
>>   fd = input_form.form_data() # not recomputed if done before
>>   form = fd.form # has applied all common expansions and renumberings
>>
>> From that point I use fd and form, never touch input_form
>> again, and never call form_data() again. Do that in FFC, and
>> you should be safe.
>
> We do something similar, but it gets a bit ugly since we want to
> modify the integral metadata (set correct representation and
> quadrature order if not already set by a user). So then we first call
> form_data() only to be able to estimate the quadrature order. Then we
> need to call form_data() again on the modified form after having
> modified the integral metadata.


This calling of form_data on the second form will result in
a new computation, which is costly.

If the metadata is the only thing you modify, can't
you store the modified metadata outside the form?


>  # Validate form
>  validate_form(form)
>
>  # Set metadata for all integrals (requires form_data().form)
>  new_form = Form([])
>  for integral in form.form_data().form.integrals():
>      new_form += Form([_set_integral_metadata(integral, options)])
>  form = new_form
>
>  # Extract form data
>  form_data = form.form_data()
>  form = form_data.form
>
>> Most algorithms work on expanded expressions,
>> but that could be documented better. Some assume
>> already expanded expressions, and some call
>> expand functions, and this is not consistent.
>> Don't hesitate to ask or report if something specific is unclear.
>
> Is it possible to either set a flag that can be checked by algorithms
> requiring expanded expressions, or that these algorithms call
> expand_compounds?
>
> It's confusing if something is required by an algorithm and it doesn't
> report an error if that requirement is not met.

That's a solution I have considered, but not found the time to go into detail.
Such flags must be possibly be propagated many places, the implementation
could be very error prone if not done carefully.

Martin