On Sep 19, 2013, at 3:53 PM, Barry Smith <bsm...@mcs.anl.gov> wrote:
> > It is essentially 3 Laplacians If you mean literally 3 scalar laplacians packed in one matrix for some reason then the one constant vector is fine. Is this a block diagonal matrix with 3 big blocks, if you order it correctly of course? > so I think the default null space of 3 constant vectors is fine. You get this if you set the block size to 3. Constant vectors in each of the three components. > 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? >