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

[Tonio Herrmann]

Thank you, Matt,
the source codes of DMPlexComputeCellGeometryFVM and your other links seem
to be very helpful. I think they answer most of my questions. I might come
back with a few more detailed questions in 1-2 weeks if that is ok with you.

Thanks
Herrmann


On Wed, Sep 7, 2016 at 4:39 PM, Matthew Knepley <knepley at gmail.com> wrote:

> 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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