ffc team mailing list archive

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

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()

?

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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