On 10 Nov 2014, at 21:48, Matthew Knepley <[email protected]> wrote:
> On Fri, Nov 7, 2014 at 11:04 AM, Lawrence Mitchell > <[email protected]>wrote: > Hi petsc-dev, > > I'm solving a pure Neumann mixed Poisson-like problem, preconditioning with a > schur complement. The pressure space has a nullspace of the constant > functions and so I attach the appropriate nullspace to the krylov solver, and > compose the constant nullspace with the IS defining the pressure space. My > RHS is consistent. > > That is supposed to work, and I think it does in my tests. The code is here > > > https://bitbucket.org/petsc/petsc/src/1f0d623c8336219eb98f7ded6f95c151ca603fe7/src/ksp/pc/impls/fieldsplit/fieldsplit.c?at=master#cl-562 > That code attaches the nullspace attached to the IS to jac->pmat if appropriate. However, if I'm using -pc_fieldsplit_schur_precondition selfp then the schur complement is preconditioned with jac->schurp (rather than jac->pmat[1]) which is not setup until here https://bitbucket.org/petsc/petsc/src/1f0d623c8336219eb98f7ded6f95c151ca603fe7/src/ksp/pc/impls/fieldsplit/fieldsplit.c?at=master#cl-656 at which point the nullspace is not attached, no? Cheers, Lawrence
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