ufl team mailing list archive

[Mikael Mortensen <mikael.mortensen@xxxxxxxxx>]

The source of truth suggests Levi-Civita, alternating or permutation symbol:
http://en.wikipedia.org/wiki/Levi-Civita_symbol

Mikael

On 13 April 2011 20:31, Martin Sandve Alnæs <martinal@xxxxxxxxx> wrote:

> That should be fairly easy to do, can be handled similarly to Identity.
>
> I = Identity(cell.d)
> f = I[i,j] * ...
>
> e = Permutation(cell.d)
> f = e[i,j,l] * v[j]*w[i]*v[l]*dx
>
> Other suggestions for naming?
>
> Martin
>
> On 13 April 2011 20:24, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
>
>> The permutation symbol should be added to UFL.
>>
>> Garth
>>
>> On 13/04/11 19:20, Martin Sandve Alnæs wrote:
>> > Python does not know anything about implicit index summation, so in your
>> > code e() is only called once, and reaches the else condition and thus
>> > returns 0.0.
>> >
>> > Similar to as_vector, you can use the as_tensor function, since you need
>> > three dimensions.
>> >
>> > Martin
>> >
>> > On 13 April 2011 19:04, B. Emek Abali
>> > <question152702@xxxxxxxxxxxxxxxxxxxxx
>> > <mailto:question152702@xxxxxxxxxxxxxxxxxxxxx>> wrote:
>> >
>> >     New question #152702 on DOLFIN:
>> >     https://answers.launchpad.net/dolfin/+question/152702
>> >
>> >     May be a non-needed trial for some, but I try to define an
>> >     expression (permutation symbol)
>> >
>> >     def e(i,j,k):
>> >            if (i,j,k) == (1.0,2.0,3.0): return 1.0
>> >            elif (i,j,k) == (2.0,3.0,1.0): return 1.0
>> >            elif (i,j,k) == (3.0,1.0,2.0): return 1.0
>> >            elif (i,j,k) == (3.0,2.0,1.0): return -1.0
>> >            elif (i,j,k) == (2.0,1.0,3.0): return -1.0
>> >            elif (i,j,k) == (1.0,3.0,2.0): return -1.0
>> >            else: return 0.0
>> >
>> >     and use (with summation over indices, it is a curl operator
>> >     contracted with w) in the form like
>> >
>> >     f=v[j]*w[i]*e(i,j,l)*v[l]*dx
>> >
>> >     which raises:
>> >     ufl.log.UFLException: Trying to integrate expression of rank 0 with
>> >     free indices
>> >
>> >     Do I have to use as_vector(...) type definition to sum with indices
>> >     or is there a nice possibility to let it sum over the arguments of
>> >     e(...) expression?
>> >
>> >     --
>> >     You received this question notification because you are a member of
>> >     DOLFIN Team, which is an answer contact for DOLFIN.
>> >
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>> >
>> >
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>
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