[petsc-users] Modified Taylor-Hood elements with piece-wise constant pressure for Stokes equation

[Justin Chang]

Actually, something is wrong. The velocity solutions are correct, but the
pressure solution has gone awry (see attached, left uses MTH whereas right
is TH). Don't know why I didn't catch this earlier, I may need to consult
to the FEniCS guys for this

On Tue, Jun 2, 2015 at 4:45 PM, Jed Brown <jed at jedbrown.org> wrote:

> Justin Chang <jychang48 at gmail.com> writes:
>
> > Last one with the svd did not work with the way the AMG PC was hard-coded
> > into FEniCS. Here's the list of preconditioners my installation of FEniCS
> > supports:
> >
> > Preconditioner    |  Description
> > ---------------------------------------------------------------
> > default           |  default preconditioner
> > ilu               |  Incomplete LU factorization
> > icc               |  Incomplete Cholesky factorization
> > sor               |  Successive over-relaxation
> > petsc_amg         |  PETSc algebraic multigrid
> > jacobi            |  Jacobi iteration
> > bjacobi           |  Block Jacobi iteration
> > additive_schwarz  |  Additive Schwarz
> > amg               |  Algebraic multigrid
> > hypre_amg         |  Hypre algebraic multigrid (BoomerAMG)
> > hypre_euclid      |  Hypre parallel incomplete LU factorization
> > hypre_parasails   |  Hypre parallel sparse approximate inverse
> > none              |  No preconditioner
>
> Wrapping an extensible dynamic system with a static maintenance burden
> is pretty much the canonical example of bad design.
>
> I used to keep a patched version of Dolfin so I could bypass this stupid
> table.  The table can and should be constructed dynamically using
>
>   const char **pcs;
>   int npcs;
>   PetscFunctionListGet(PCList,&pcs,&npcs);
>
> Anyway, are you sure this wasn't fixed so that you can pass PETSc
> options directly?
>
> If you can get commands to PETSc, but just can't change the
> preconditioner, then try
>
>   -ksp_view_mat binary
>
> (for the tiny problem) and open the resulting matrix "binaryoutput" in
> octave/matlab/scipy.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20150602/b175bae0/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: stokes_iter_pressure.png
Type: image/png
Size: 108344 bytes
Desc: not available
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20150602/b175bae0/attachment-0001.png>