Hi Roy,

The nonlinear Navier-Stokes equation is a difficult problem.  It is nonsymmetric
and with strong convection can create a mess.  Much research has gone into solving
this problem using AMG as well as many other solvers and if you are interested you
could find a number of papers on what is required of AMG to work well.

AMG was originally defined for symmetric positive definite problems and once you
get outside of that realm you should take a look at what others have done.  I have
a colleague who has done work on Navier-Stokes and MG and I'm waiting for his
opinion.  Is it possible to try regular multigrid on this problem and if so how does
it perform?  Just curious.

Cheers, Travis

----- Original Message ----
From: Roy Stogner <roystgnr@ices.utexas.edu>
To: Travis Austin <austint73@gmail.com>
Cc: libmesh-users@lists.sourceforge.net
Sent: Wednesday, February 28, 2007 1:02:49 PM
Subject: Re: [Libmesh-users] Algebraic multigrid

On Thu, 22 Feb 2007, Travis Austin wrote:

> Please note that you must have a recent version of petsc (2.3.x) that is
> compiled with HYPRE support.  Earlier versions of petsc do not make room
> for HYPRE use.

I note that one probably should also have a more intimate knowledge of
HYPRE than I do - on the first complicated example problem I tried (3D
lid-driven cavity incompressible flow), the linear symmetric Stokes
flow case was unbelievably faster using multigrid, but as soon as I
turn on the nonlinear/nonsymmetric Navier-Stokes convection term,
something goes wrong.  The KSP residuals say I'm converged, but Newton
doesn't think that the result is even necessarily a descent direction.

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