ffc team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

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. Better would be

    a.preprocess()

or

    a.form_data()

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?
>>>>>