[petsc-dev] SNES for 2x2 problems

[Matthew Knepley]

On Wed, Jan 2, 2013 at 3:21 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> Matt, you know how we always tell people not to use KSP (or even Lapack)
> for 2x2 problems? Surely the same advice applies to SNES, but your point
> location code is doing it.
>

Yep. The wrapping overhead is far less with some Newton iterations, and we
have no good alternative.


> Also, please remember to test that complex actually works before declaring
> it fixed. I just cleaned up a bunch more stuff, including pain invoked by
> SNES operating in PetscScalar for those 2x2 point location problems.
>
>
> https://bitbucket.org/petsc/petsc-dev/commits/0213b4504a412b7304d6032d6047079603a8c2c8
>

We need to get mixed-mode working. This kind of programming is far to
inconvenient and ugly, especially
for small side problems like these that are never ever ever intended to
support complex.


> To be vectorization-friendly, I would write point location to operate
> directly on a batch of points, wrapped in the little Newton loop (not
> SNES). Maybe this implementation of yours is a reference that you're
> planning to replace?
>

Yes, this is for a very small number of point locations necessary for
seismic sources, not intended for
inter-mesh interpolation or anything that fills up the mesh.

   Matt

-- 
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20130102/52afcc43/attachment.html>