[petsc-dev] 6-node wedge cells in DMPlex

Matthew Knepley knepley at gmail.com
Thu Jan 26 08:04:15 CST 2017

On Wed, Jan 25, 2017 at 11:12 PM, Adrian Croucher <a.croucher at auckland.ac.nz
> wrote:

> hi Matt,
> A couple of years ago we discussed adding support for 6-node wedge cells
> in DMPlex- the hurdle being that at present DMPlex doesn't support cells
> with faces of different shapes (see below)- and you said it could be done,
> if and when I needed it.
> People are starting to want to use my code on real models now, many of
> which have 6-node wedge cells. So it would be very handy to have support
> for those in DMPlex fairly soon if possible.
> Any chance you would be able to take a look at it? In principle I would be
> happy to help if I can. I have started looking at plexinterpolate.c to try
> and see how it works, but at this stage I'm not at all confident that I
> understand the subtleties.
Okay. First I need to understand exactly what shape we want to handle. Can
you draw it or explain precisely?

Second, we need to prescribe a total order on the vertices for a wedge, and
then a set of faces as ordered arrays of vertices.
That information goes here:


I think that might be all we have to do, but until you try something,
secret assumptions lurking in the code are not obvious.



> Cheers, Adrian
> On 16/04/14 08:42, Matthew Knepley wrote:
> Yeah, I was afraid that might be the workaround ;-) It seems to me that
> for a large unstructured mesh, creating the whole DAG would basically
> amount to duplicating what the very handy DMPlexInterpolate() function does.
> The problem here is that if I allow faces of different shapes, I have to
> keep track of the shape of each
> face when I make it. This is possible,  and I have added it to the TODO
> list, but I think it will be a while
> before I get to it. If you want to try doing it, I would help.
> I'd have to get more familiar with how it works first, and it probably
> isn't top of my priority list either at present- I can continue getting my
> code together without support for wedge cells at the moment. But at some
> point I will need it.
> Okay, when you need it, we will make it work.
> --
> Dr Adrian Croucher
> Senior Research Fellow
> Department of Engineering Science
> University of Auckland, New Zealand
> email: a.croucher at auckland.ac.nz
> tel: +64 (0)9 923 4611 <+64%209-923%204611>

What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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