[petsc-users] MatGetDiagonalBlock and shell matrices

[Steven Dargaville]

Hi all

I'm just wondering if there is any plans in the future for
MatGetDiagonalBlock to support shell matrices by registering a
user-implemented MATOP? MatGetDiagonal supports MATOP, but the block
version of this does not.

I found a previous query on the user list which touched on this and
mentioned that it would be easy to add:

http://lists.mcs.anl.gov/pipermail/petsc-users/2011-May/008700.html

I have implemented a matrix-free multigrid algorithm using shell operations
in PETSc, and it would be very convenient to be able to provide a local
shell Mat so I could apply local GMRES (or other matvec-based solvers) as a
local block smoother.

Thanks!
Steven
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