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

[Barry Smith]

  After talking to Mark I think this will not work. Without a block size GAMG will not do a good job aggregating the graph.   

  Mark suggested leaving those rows and columns in the matrix zeroing its rows and columns (except the diagonal) instead then call GAMG with the block size of 3.

   Barry

On Sep 19, 2013, at 3:56 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> Barry Smith <bsmith at mcs.anl.gov> writes:
> 
>>   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.
> 
> Yup, that's what I would try.