[petsc-dev] coarse grid in gamg (for the OPTE paper)

[Barry Smith]

   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 <jedbrown at mcs.anl.gov> wrote:

> Barry Smith <bsmith at 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?