[petsc-dev] Non-scalable matrix operations

[Jed Brown]

On Fri, Dec 23, 2011 at 10:48, Mark F. Adams <mark.adams at columbia.edu>wrote:

> There is the implementation in Prometheus that uses my C++ linked lists
> and hash tables.  I would like to implement this with STLs.  I also hack
> into MPIAIJ matrices to provide a primitive of applying G-S on an index set
> of local vertices, required for the algorithm.  This should be rethought.
>  I would guess that it would take about a week or two to move this into
> PETSc.
>
> The complex communication required make this code work much better with
> large subdomains, so it is getting less attractive in a flat MPI mode, as
> it is currently written.  If I do this I would like to think about doing it
> in the next programming model of PETSc (pthreads?).  Anyway, this would
> take enough work that I'd like to think a bit about its design and even the
> algorithm in a non flat MPI model.
>
> Note, I see the win with G-S over Cheby in highly unsymmetric (convection,
> hyperbolic) problems where Cheby is not very good.
>

Can we mix with Eisenstat to apply multiple cycles? I know the theory
doesn't argue for it, but G-S with Cheby sometimes wins over everything
else I've tried. Is there any hope of doing nonlinear G-S where the user
can provide something moderately simple?
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