dolfin team mailing list archive

[Kristian Ølgaard <k.b.oelgaard@xxxxxxxxx>]

On 8 June 2011 14:08, Martin Sandve Alnæs <martinal@xxxxxxxxx> wrote:
> On 8 June 2011 13:55, Martin Sandve Alnæs <martinal@xxxxxxxxx> wrote:
>> On 8 June 2011 13:46, Kristian Ølgaard <k.b.oelgaard@xxxxxxxxx> wrote:
>>> On 8 June 2011 13:31, Martin Sandve Alnæs <martinal@xxxxxxxxx> wrote:
>>>> On 8 June 2011 13:11, Kristian Ølgaard <k.b.oelgaard@xxxxxxxxx> wrote:
>>>>> On 8 June 2011 12:11, Martin Sandve Alnæs <martinal@xxxxxxxxx> wrote:
>>>>>> Done and checked in. If someone updates FFC to support this, we can
>>>>>> hopefully close this bug.
>>>>>
>>>>> I'm not sure this is enough to handle the bug. If you look at the
>>>>> output of printing M in the example code I posted you'll see that the
>>>>> list tensor contains component '7'. This is what you'll get from
>>>>> calling self.component(), but the
>>>>> TT.symmetry() only contains:
>>>>> {(2,): (1,), (6,): (5,)}
>>>>>
>>>>> Is there some function we need to call first to map the component '7'
>>>>> --> '6', before looking at symmetries to map '6' --> '5'?
>>>>> Doing so will get us into trouble with mapping '3' --> '2' since
>>>>> symmetry will map that to '1'.
>>>>> The TT element has 2 x 3 sub elements due to symmetry.
>>>>
>>>> The 7 is an index into the value index space of the coefficient and is
>>>> correct. It has nothing (directly) to do with subelement indexing. I
>>>> think you're assuming a closer relation between them than there is?
>>>> Let me try to clear it up...
>>>>
>>>> The value index space is contiguous from the point of view of UFL
>>>> expressions, but has holes when symmetries are considered. The
>>>> noncontiguous value index space will then need to be mapped to a
>>>> contiguous subelement space by associating each value index that is
>>>> not in the symmetry mapping with a subelement index.
>>>>
>>>> 1) We have a component/value index
>>>> 2) We map that value index to another value index using a symmetry
>>>> mapping (e.g. 6->5 and 7->7 in your example)
>>>> 3) We map from the noncontiguous value index space to the contiguous
>>>> subelement index space
>>>>
>>>> Clear as mud? :)
>>>
>>> Yes, but since we only deal with the (sub)elements that are actually
>>> present in FFC, it's really inconvenient that we can't get a mapping
>>> from the component to the subelement.
>>> I somehow suspected the FiniteElement.extract_component() to do this,
>>> but it turns out not to be the case.
>>>
>>>> UFL handles (2) for you only when you apply expand_indices.
>>>>
>>>> FFC will have to handle (3) when generating code, it doesn't touch
>>>> anything UFL needs to know about. I'll see if I can whip up a quick
>>>> utility function for it though.
>>>
>>> That would really be nice.
>>
>> Done :) The latest patch contains code and test showing usage.
>>
>> But maybe it should be integrated into extract_component, I'll take a
>> look at that now that I'm into this.
>
> I applied the symmetry mapping inside extract_component for tensor elements,
> that way you shouldn't have to do the symmetry mapping in addition to
> calling extract_component. The numbering utility I checked in could still
> come in handy though, so I'll let it stay.

OK, will you add the numbering utility function in extract_component such that
calling this function will return the contiguous component and element?

> Note that when I pushed now I pushed the float formatting fix as well,
> so some FFC references will probably need regeneration again :)

Yes, I noticed that :)

Kristian

> Martin
>