[petsc-users] unreliable AMG in PETSc

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:
>    It is any interesting question if there is anything one can “do” to
>    a preconditioner to insure that it is SPD or detect if it may not
>    be BEFORE actually running the CG with that preconditioned. 

You can use an eigensolver for the extreme eigenvalues of the iteration
matrix for the smoother.  And if it's unstable, report that.  This is
one thing that the petsc-eig plugin (which I'll update) can do, but it's
too expensive to do by default.
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