[petsc-users] Neumann BC with non-symmetric matrix

[Mark Adams]

>
>
>    4-4) Along the same lines, I tried a couple of other PCs such as
> {jacobi, sor, gamg, ilu} and none of them were able to converge with bcgs
> as the KSP. However, with gmres, almost all of them converge with the
> exception of gamg.
>

Note, I'm not sure why you need the null space of A^T, you want the null
space of A.

And for singular systems like yours you need to use a pseudo inverse of the
coarse grid because it is singular -- if you represent the null space
exactly.

GAMG is use for AMR problems like this a lot in BISICLES.

You need to use an 'svd' coarse grid solver, or an appropriate iterative
solver. LU is the default.

Mark
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