It is essentially 3 Laplacians so I think the default null space of 3 constant vectors is fine. The problem is without the block information presumably GAMG is using only a single constant vector over all variables? So maybe we need to construct a 3 vector null space which just marks in the reduced vector from which of the 3 components each entry came from.
Barry On Sep 19, 2013, at 3:48 PM, Jed Brown <jedbr...@mcs.anl.gov> wrote: > Barry Smith <bsm...@mcs.anl.gov> writes: >> That is what it is doing and apparently it doesn't result in a good >> preconditioner; I don't know why off hand. One thing is it no >> longer knows about the block structure. > > How is the near null space being specified?
