[petsc-users] Null spaces with fieldsplit preconditioning
Lawrence Mitchell
lawrence.mitchell at imperial.ac.uk
Wed Mar 12 06:44:06 CDT 2014
Hello,
I have a mixed FEM system, for which the null space is constant
functions in one of the sub spaces. That is, I have W = V * Q and the
null space is a constant function in Q (and zero in V). If I assemble
the operator, I get a block structure:
X = [A B,
C D]
When I solve this monolithically, I project the null space out by
attaching it to X. However, if I use Schur complement preconditioning,
then S = D - C Ainv B has a null space of the constant functions as
well. Do I therefore need to attach null spaces to both X and S in this
case, or will attaching it to X be enough? If I do need to hang
something on S, is there an easy way to do it?
Cheers,
Lawrence
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