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[Martin Sandve Alnæs <question152702@xxxxxxxxxxxxxxxxxxxxx>]

Question #152702 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/152702

    Status: Open => Answered

Martin Sandve Alnæs proposed the following answer:
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>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?
>
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