For vector elements, the jump() operator in UFL is defined as follows:
dot(v('+'), n('+')) + dot(v('-'), n('-'))
I'd like to argue that it should instead be implemented like so:
outer(v('+'), n('+')) + outer(v('-'), n('-'))
That would enable writing the natural term appearing in DG/Nitsche
formulations for vector-valued problems as follows:
inner(avg(grad(u)), jump(v, n))
This would be analogous to the scalar case which is written
dot(avg(grad(u)), jump(v, n))
With the current implementation, the term for vector-elements must be
implemented like this:
dot(dot(avg(grad(u)), n('+')), jump(v))
Is the current version of jump() for vector elements implemented as it
is for a particular reason, or can we change it?
--
Anders
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