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[Martin Sandve Alnæs <question158115@xxxxxxxxxxxxxxxxxxxxx>]

Question #158115 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/158115

Martin Sandve Alnæs proposed the following answer:
But note that fenics only supports facet normals that are constant
over each facet.

So this should be the same:
  u.dx(i,j)*n[i]*n[j]
or
  dot(n, grad(dot(grad(u), n)))

Martin

On 19 May 2011 08:27, Martin Sandve Alnæs <martinal@xxxxxxxxx> wrote:
> Hi Gerard.
> Use index notation instead of the grad operator:
>
> (u.dx(i)*n[i]).dx(j)*n[j]
>
> And that should work fine.
>
> Mixing of "compound operators" that create expressions
> with a tensor shape, with index notation which deals with
> "sets of scalars", will not always work. Some times it is
> ambiguous. In this case, should it work? Could be a bug, not sure.
>
> Martin
>
> On 19 May 2011 00:35, Gerard Awanou
> <question158115@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> New question #158115 on DOLFIN:
>> https://answers.launchpad.net/dolfin/+question/158115
>>
>> I am running the Fenics demo written for C^0 Discontinuous Galerkin
>> method for the biharmonic equation. I understood that the demo is for
>> the boundary condition \Delta u =0. For a boundary condition \partial
>> u/\partial b =0, it seems that one should use the formulation in
>>
>> C0 Interior Penalty Methods for Fourth Order Elliptic Boundary Value
>> Problems on Polygonal Domains by Brenner and Sung
>>
>> To do this I need to compute n'(D^2 u)n (p. 100 of the paper).
>> I tried n[i]*( grad(grad(v))[i,j]*n[j]) without success.
>> How do you compute \partial^2 u/\partial n^2  where n is the unit
>> outward normal to an edge?
>>
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>

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