[petsc-dev] petsc-dev fails test with debugging=0

[Karl Rupp]

Hi,

 >> I want to use KSPGMRES
>
> With what inside?  Jacobi?
>
> Your outer solve was GMRES, which requires a linear preconditioner.
> That implies fully converging the subdomain solver when using an
> iterative method.  This is likely to be inefficient, in which case you'd
> probably want to switch to FGMRES or GCR for the outer KSP.
>
> I don't know how difficult it will be to make BJacobi support GPUs.
> Could be easy, but someone has to write the code.  Karl or Dominic, have
> you looked at this?

It depends on the amount of stability one wants to put it. If Gauss 
without pivoting is sufficient, Block-Jacobi shouldn't be too hard for 
the block size of interest (9-by-9). However, I suppose we do want 
robust solves, so it's better to use some explicit solution formulas. 
Cramer's rule is okay up to 4-by-4 blocks or maybe 5-by-5, but likely to 
be a mess for 9-by-9.

Best regards,
Karli