Ben,
I'm trying to add a single DoF to my Trilinos system (not associated with the
FE system, similar to the question asked here
<https://groups.google.com/d/msg/dealii/FpDMRyhsmqI/XqiHH2qZpWEJ>). I followed
the advice there, and set it up as a block system, where block (0,0) is the
usual FE matrix, and block (1,1) is a 1x1 "matrix". Setting this up to work in
parallel with Trilinos was tricky, but I got it working by using the usual
partitioning IndexSet and an IndexSet with 1 entry owned by processor 0, which
I use to reinit the new matrix blocks (the 1x1 block, and the 1xn and nx1
off-diagonal blocks).
The code I've written works, however, as I've scaled up the system it's become
a huge bottleneck.
Can you elaborate? Is it setting up the matrices that is the bottleneck, or
solving the linear system?
If it is solving the linear system, have you thought about forming the Schur
complement with regard to the 1x1 block? This will just yield a rank-1 update
to the other diagonal block.
Best
W.
--
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Wolfgang Bangerth email: bange...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/
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