"Young, Matthew, Adam" <[email protected]> writes: > Should I be using MatSetNearNullSpace (as opposed to MatSetNullSpace) with > -pc_type hypre -pc_hypre_type boomeramg since BoomerAMG is multigrid?
As far as I know, Hypre doesn't directly use either of these. MatSetNullSpace is for an actual null space. It is usually set so that the Krylov method can clean any pollution caused by the preconditioner. MatSetNearNullSpace is for things like rigid body motions which are sort of a local null space (i.e., it would be a null space with some different boundary conditions, like natural/floating). It is used by aggregation-based multigrid methods.
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