[petsc-users] multigrid questions

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:
>    For optimal implementation of line relaxation (assuming each
>    process is only doing sequential lines) you would write a PCSHELL
>    that looped over the "lines" for your geometry and use inside it a
>    PC created with the tridiagonal matrix for a line. 

Or (less code) assemble a Pmat that skips insertions across lines.  That
will make a bunch of tridiagonal segments on each process and a direct
solver will be trivially cheap (ILU(0) is a direct solver).
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