[petsc-users] Convergence of transposed linear system.

[Gaetan Kenway]

That's not a bad idea. I'll try that on the large RANS adjoints.

However, I have been trying to replicate the same sort of behavior on
smaller Euler meshes (~500k DOF) and  I have been somewhat successful is
replicating the same sort of issue, although the effect isn't as severe.
For these cases, even with a single processor with an ILU(1)
preconditioner, I'm seeing different convergence rates. Obviously in this
case the ASM isn't the culprit. I still need to do a bit more digging to
try to get to the bottom of this. When I get something, I'll post it.

Thanks,
Gaetan

On Wed, Nov 26, 2014 at 11:10 AM, Jed Brown <jed at jedbrown.org> wrote:

> Gaetan Kenway <gaetank at gmail.com> writes:
> > The untransposed system converges about 6 orders of magnitude with
> > GRMES(100), ASM (overlap 1) and ILU(1) with RCM reordering. The test is
> run
> > on 128 processors.  There are no convergence difficulties.
> >
> > However, when I try to solve the transpose of the same system, by either
> > calling KSPSolveTranspose() or by assembling the transpose of the linear
> > system and its preconditioner and calling KSPSolve(), GMRES stagnates
> after
> > a negligible drop in the residual and no further progress is made.
>
> Just a guess here, but the ASM default is "restricted ASM".  Can you
> compare the nontransposed and transposed convergence with each of
>
>  -pc_type <restrict,basic,interpolate>
>
> I.e., 6 runs in total; how does each converge or not?
>
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