I am using discontinuous elements on a regular mesh. Given a degree of
freedom that I know lies on a given cell and face (technically has
support on that face, as this is dG) I would like to find out which dof
is its neighbour i.e. the equivalent dof from the cell adjoining across
the given face.
It is not difficult to loop through all of the cells, then faces then
dofs and find the dofs with support on a given face. It is not
difficult to then extract the neighbouring cell and find which dofs from
that cell also lie on the face. However, what is the best way to find
which dof matches which dof. For example, in 2d using linear dG
elements each face has 2 dofs with support on that face from one cell,
and two from the neighbouring cell. I would like to know how they are
matched so I can add constraints.
There are several very long ways to do this, but does anyone know of a
deal.ii function which can be given a cell, face and dof and return the
equivalent dof from the neighbouring cell? I could write my own loop by
either extracting the true location of the dof, or by using knowledge of
how the dofs are numbered (i.e. in x first, then y, then z if it
exists), but would prefer to use a pre-existing function.
If any of this isn't clear, I can post some code, but I have avoiding
doing so now as what I have doesn't currently do what I want!
Thanks,
John
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