[petsc-dev] higher-order coordiate fields in DMPlex

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:

> On Fri, Jun 2, 2017 at 7:55 PM, Jed Brown <jed at jedbrown.org> wrote:
>
>> Matthew Knepley <knepley at gmail.com> writes:
>>
>> > On Fri, Jun 2, 2017 at 5:04 PM, Alberto Paganini <
>> > Alberto.Paganini at maths.ox.ac.uk> wrote:
>> >
>> >> Dear PETSc developers,
>> >>
>> >> I'm Alberto and I'm a user of the finite element library Firedrake,
>> >> which relies on DMPlex to import meshes.
>> >>
>> >
>> > Great.
>> >
>> >
>> >> In order to use higher-order FEs, it is desirable to import higher-order
>> >> meshes.
>> >>
>> >
>> > I really do not like that term. Let me try and convince you that it is
>> > wrong. The topology of the
>> > mesh is unchanged. You are only talking about the order of the
>> > representation of the geometry
>> > field. Thus, it is not the mesh that is "higher order", but the geometry.
>> >
>> >
>> >> I've been told that DMPlex does not offer this future (at present).
>> >>
>> >
>> > Toby just merged this to master, so I think we can say that we have alpha
>> > support for this. How
>> > does it work? We already have a coordinateDM and coordinates Vec, so you
>> > just choose a
>> > higher order discretization for the DS inside the coordinateDM. Does that
>> > make sense?
>>
>> Can it load quadratic geometry from a file (ExodusII or otherwise)?
>>
>
> If someone requests a given file format, we can do it. That's how we always
> proceed.

Okay.  When people ask about higher order geometry for unstructured
finite elements, I think that about 90% of the time they're really
asking whether it can read quadratic geometry from a file.  I hate that
ExodusII is a cumbersome dependency, but it might be the most useful to
add.  This wouldn't be just cosmetically checking a box because this can
make a big accuracy difference -- quadratic elements have a really hard
time paying off for engineering problems if you don't also have
quadratic geometry.
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