[petsc-users] PCSORSetSymmetric

[John Fettig]

I don't really understand what is the purpose of the "local" options
in PCSOR. In serial for AIJ for example, SOR_FORWARD_SWEEP and
SOR_LOCAL_FORWARD_SWEEP appear to follow the same path in the code.

In parallel for MPIAIJ, SOR_FORWARD_SWEEP isn't even handled by
MATSOR_MPIAIJ().  It actually results in a segfault if you try it
(this looks like a bug), for example in ksp/ksp/examples/tutorials:
"mpirun -np 2 ./ex2 -pc_type sor -pc_sor_forward"  So in parallel, the
only valid options are the "local" ones, which makes sense since you
haven't provided a true parallel SOR.

What is the purpose of the "local" options then, if there really isn't
a "global" SOR?

Thanks,
John