[petsc-dev] MetSetBlockSize issue

[Mark F. Adams]

On Apr 25, 2012, at 7:15 PM, Jed Brown wrote:

> On Wed, Apr 25, 2012 at 17:58, Mark F. Adams <mark.adams at columbia.edu> wrote:
> The blocks are not always dense, so by what appears to be your definition of block size it is not (always) a 'column block size'.   But I think that it is  semantically a blocked matrix and hence it has a column block size.
> 
> I think we shouldn't try to encode the near-null space being sparse. For elasticity, we would only reduce the 18 matrix entries to 12, which is only about break-even on storage since the dense null space can use fewer column indices (this is ignoring the dense case also being more efficient).

Its worse than that in aggregation MG, I think, because P is not the null space but Q in a QR decomposition of the rigid body modes ... that might still have some sparsity, not sure.
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