[petsc-users] Off-diagonal matrix-vector product y=(A-diag(A))x

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:

>    You can do MatGetDiagonal() then do a MatMult() followed by
>    subtracting a VecPointsizeMult(). 

I would use VecPointsizeMult followed by MatMultAdd.  One fewer
traversal of a vector.
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