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

[Mark F. Adams]

>>> 
>>> results in two levels with the coarse problem being 13*13. Wouldn't
>>> it be natural for the coarse problem to be of size that's an integer
>>> multiple of 3, though?

Yes, something is wrong here.  And as Jed said if you have different Mats for the operator and preconditioner the you have to set the block size on the preconditioned Mat.  If you are then we have a problem.

> 
>>> 2) For the specific set of parameters I'm using for testing purposes,
>>> the smallest nonzero entry of the finest level matrix is of order
>>> e-7.

BTW, the scaling of the matrix should not matter.  If you see a difference then we would want to look at it.

>>> For the coarse level matrix (size 13*13), whose entries are
>>> determined by MatPtAP called in createlevel (in gamg.c), the smallest
>>> nonzero entry is of order e-24 - this jumped out at me as a potential
>>> sign of something wrong.

Oh, you are talking about the smallest.  That does not matter.  (its a sparse matrix so technically the smallest entry is zero)

> 
> What does -mg_coarse_pc_type svd -mg_coarse_pc_svd_monitor tell you
> about the condition number of the coarse operator?  Send -ksp_view.