On Wed, Apr 25, 2012 at 19:46, Mark F. Adams <mark.adams at columbia.edu>wrote:
> 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. > Well, the translational modes are position-independent, so they should retain sparsity with a standard implementation of QR (in the sense that the zeros will remain very close to 0 so that you could discard them, though I don't think it's even worth trying to do that). -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20120425/c8f09e11/attachment.html>
