[petsc-users] Convergence of transposed linear system.

[Jed Brown]

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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