Dear All,

	There has been a lot of independent activity on elliptic solvers
lately.  They are still one of our major bottlenecks (sometimes 95% of run
time!), and they are increasingly needed:  maximal slicing is still one of
the most successful slicings,  and new work in Palma with eigenmethods
relies on it, too;  an entire family of shift conditions involves coupled
ellitpptics; and recently Kip Thorne has been visiting us in Potsdam and
has some proposal for gauge conditions that involves 3 or 4 coupled
elliptics that we want to try out.

	I just had a long talk with Dan Bullok and Paul Saylor at Illinois
on Friday.  Dan plans to take a look at our elliptic problems over the
summer, and would like to get started soon.  He has developed his own
"patch" multigrid solver that can interface to Cactus through Petsc.  I
brought him up to date on Bernd's BAM multigrid solver, and he would like
to take a look at it to see if he might have some ideas about optimizing
it.  Bernd, could you help point Dan to the minimal setup he would need to
check it out, with say, maximal slicing in Cactus?

	Gerd and Mark, could assist Dan if he needs some help with Cactus?

	At the same time, Paul wrote a Matvec operator that would hook
directly to our matrix setup for elliptics.  Faisal and Paul have discussed
using this as the core of an iterative package we could put together, like
CMstab was in the old G code.  Dan might be able to easily write some
simple CG based iterative solvers around that that we could experiement
with.   Paul, could you point Dan and the rest of us to that?

	Dan's own multigrid solver might be used through Petsc, or perhaps
directly through our elliptic solver interfaces in Cactus.  Paul, Mark,
Bernd, it would be helpful if you could lend a hand to Dan to see what
would be required to connect it directly as a thorn.

	Finally, having all this together would allow us to experiment with
different ways of solving elliptics, possibly ussing MG as a preconditioner
for iterative solvers, with Petsc or our own home grown solvers.  I suspect
they all would have some use, some strngths, and weaknesses.

	Let us try to organize this and march forward.

	Thanks,
	Ed

	I am planning to be really running simulations this summer where
elliptic will probably play an important role.  I am very anxoious




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Ed Seidel
Max-Planck-Institut fuer Gravitationsphysik
Albert-Einstein-Institut
Schlaatzweg 1
D-14473 Potsdam, Germany
Tel. +49-331-27537-13
Fax +49-331-27537-98
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