[petsc-users] beginner's, technical programming manual?

[Matthew Knepley]

On Mon, Sep 5, 2016 at 12:52 PM, Tonio Herrmann <tonioherrmann at gmail.com>
wrote:

> Hello,
> I am new to PETSc, and I am struggling to use it for some numerics
> problems. The mathematical capabilities are well explained in the manual,
> in several tutorials and examples.
>
> But I am stuck at every tiny step, because I cannot find the required
> functions for all the very basic technical details, like getting the vertex
> coordinates of a DMPlex, the face areas and cell volumes (if available
> through PETSc?). Merging two DMPlexes, that share a common boundary, into
> one. Extracting a boundary of one DMPlex as a new DMPlex. Etc.
>

Hi Hermann,

There is currently no introduction of the kind you want. Everything I have
written is geared towards solving PDEs because that
it what I do with most of my time, and it is what I get the most questions
about. However, there are some resources:

a) Papers

         http://arxiv.org/abs/0908.4427
         http://arxiv.org/abs/1506.07749
         http://arxiv.org/abs/1508.02470
         http://arxiv.org/abs/1506.06194

b) Manpages

For example, you can get the coordinates of a DM using


http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DM/DMGetCoordinates.html

http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DM/DMGetCoordinatesLocal.html#DMGetCoordinatesLocal

or compute things like volumes or face areas,


http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DM/DMPlexComputeCellGeometryFVM.html

or extracting the boundary


http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DM/DMPlexCreateSubmesh.html

c) Examples

There are a lot of examples, like SNES ex12, ex62, ex77 where we use these
operations to solve PDEs.

There is no operation for merging two Plex objects, but it would not be
hard to write, if you marked the common
boundary in both using a DMLabel. Plex is intended to be transparent enough
for users to write new operations
like these.

  Thanks,

      Matt

Is there any technical introduction that shows how to deal with the data
> structures on a basic, geometrical and topological level without
> necessarily discussing the numerics of PDEs and equation systems?
>
> Thank you
> Hermann
>



-- 
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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