[petsc-users] Refinement, interpolation, and auxiliary data

[Matthew Knepley]

On Tue, Jan 20, 2015 at 3:06 AM, Justin Chang <jychang48 at gmail.com> wrote:

> Hi all,
>
> I have a few simple questions regarding DMPlex mesh refinement,
> interpolation, and auxiliary data:
>
> 1) What exactly does DMPlexSetRefinementUniform do? Is it relevant only
> for the DMPlexCreateBoxMesh() function?
>

Plex supports two types of refinement now. First, you can call a mesh
generator for refinement, like Triangle or TetGen. Second,
you can uniformly refine cells, although I have only coded this for
simplices and tensor products. The uniform refinement works
on any mesh, not just the builtin ones.


> 2) When I interpolate a given DMPlex mesh, what becomes of the "boundary"
> edge/face labels and/or IDs? That is, say if I had a 2D simplex element on
> the boundary domain and two of its vertices are assigned different marker
> ID's and/or labels, what will become of those intermediate mesh point(s)
> become?
>

I do not mark them. That is up to the application, since there is no way to
do it generically. What I do in my simple code is to use
MarkBoundaryFaces() and LabelComplete(). For complex things, I use the
ExodusII format for marking faces.


> 3) If I have highly heterogeneous diffusivity or permeability (e.g.,
> random permeability or a marmousi
> <http://www.caam.rice.edu/~benamou/OLD/marmousi.html>data set) that need
> to be read in as auxiliary coefficients, would I need to manually
> interpolate the data for the intermediate mesh points before I project the
> field into the FE space, or does PETSc have an ability somewhere to
> automatically interpolate these values for you?
>

You have to explain more about what this data means. Is it cell-wise data?
If so, why do you need to interpolate?
Shouldn't it just be in P0? If not, you can project the P0 data into any
other space using either ProjectFunction()
or a slightly modified version of DMPlexComputeInterpolatorFEM().

  Thanks,

     Matt


> Thanks,
> Justin
>



-- 
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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