[petsc-users] PETSc on unstructured meshes / Sieve

[Marek Schmitt]

Thank you very much for the reply. However, I am even more confused now.

Fenics is built on top of PETSc, 
isn't it? Then why do they use different Sieve implementations? Is one 
of the implementations much more advanced than the other, and if yes, 
could you show me some mailing list discussion or other information 
where the two are compared? (An acronym like "PETSc" is much easier to 
search for than "sieve")


How is it meant that Sieve is 
"nowhere near the level of clarity and robustness that the rest of PETSc has"? Is it just that PETSc has very high standards that are not met by Sieve, or does Sieve have any major flaws or drawbacks? I just want to 
make sure that I don't work in impassable terrain.

Marek

________________________________
From: Matthew Knepley <knepley at gmail.com>
To: Marek Schmitt <marek.schmitt at yahoo.com>; PETSc users list <petsc-users at mcs.anl.gov>
Sent: Wednesday, August 24, 2011 3:45 PM
Subject: Re: [petsc-users] PETSc on unstructured meshes / Sieve


On Wed, Aug 24, 2011 at 1:25 PM, Marek Schmitt <marek.schmitt at yahoo.com> wrote:

I would like to experiment with PETSc for learning FVM on unstructured grids. I get the impression that PETSc is primarily developed for structured grids with cartesian topology, is this true?
>

PETSc is not primarily developed for discretization and topology. It solves systems of nonlinear algebraic equations. It does have
some extensions that handle structured (DMDA) and unstructured (DMMesh) under the recently developed DM interface.

Pylith and Fenics seem to use Sieve for unstructured grids. Is Sieve part of PETSc?
>

Sieve is both the name of an interface (implemented by FEniCS) and an implementation of that interface (in PETSc).

Why is it so much hidden? The very silent sieve-dev mailing list exists since four years, but there is a recent post:
>

I am not sure its hidden. I answer all the questions on the list. Its a big project for one person to support. I put most of
my time into supporting PyLith (http://geodynamics.org/cig/software/pylith) which uses it for parallel FEM simulation.
PETSc is 20 years old, so we have had time to make some components more robust.

"2) Unstructured meshes. This is not well-documented. There is a tutorial presentation and a repository of code for it. A few people have used this, but it is nowhere near the level of clarity and robustness that the rest of PETSc has." (from http://lists.mcs.anl.gov/pipermail/sieve-dev/2010-October/000098.html)
>Is the sieve-dev list about a different sieve than what is used by Pylith and Fenics?
>

They are two different implementations.

There is a PETSc FAQ "Do you have examples of doing unstructured grid finite element computations (FEM) with PETSc?". It mentions Sieve but no further links or documentation.
>
>Is the directory petsc-3.1-p8/include/sieve all that is needed to work with Sieve? Or are these only header files, and I have to link to the Sieve library from somewhere else (then where can I find Sieve)?
>

You must use petsc-dev in order for the examples to work, like SNES ex12.

  Thanks,

      Matt

Please shine some light into the mysterious Sieve.
>Marek
>


-- 
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