[petsc-users] GAMG

[Mark Adams]

>
>
> The labeling is right, I re-checked. That's the funny part, I can't get
> GAMG to work with PCSetCoordinates (which BTW, I think its documentation
> does not address the issue of DOF ordering).
>

Yep, this needs to be made clear. I guess people do actually look at the
manual so I will add that.

As far as symmetry and BCs. If all dofs are set at a node, so the node is
all zero when you zero out BC's, then this should cause a problem in
parallel (you may need several processor to hit the problem). You really
should remove them from the matrix and adjust the RHS accordingly, but if
you set -pc_gamg_threshold X to a negative number (default is zero) and
keep the zeros in the matrix after zero out rows then it should work (the
graph algorithms will keep your zero node so the graph is symmetric).
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