[petsc-dev] access to finite element second derivatives

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:
> So these elements are C1? I would have a tendency to fall back on mixed
> formulations or interior penalty (I don't understand these) formulations for
> this. Then C0 elements are alright.

C^1 elements can be delicate beasts, though they wouldn't be hard to
express now.  Second derivatives would be useful even for C^0 elements,
to evaluate some error estimators and to provide stabilization terms
like SUPG (with high-order elements).

I have always disliked having separate tiny functions for each of the
entries.  Once you add second derivatives, it is painfully obvious that
humans will not be coding all those tiny functions, at which point it is
clearly not the right interface.
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