On Fri, Nov 6, 2015 at 9:29 AM, Denis Davydov <[email protected]> wrote:
> > > On 6 Nov 2015, at 16:22, Matthew Knepley <[email protected]> wrote: > > > > Is it possible that the matrix is rank deficient? Jacobi will just chug > along and sometimes work, but > > AMG will fail spectacularly in that case. > > It should not. It is just a mass (overlap) matrix coming from linear FEs > with zero Dirichlet BC assembled in deal.II. > Due to elimination of some algebraic constraints on DoFs there are lines > with only diagonal element, > but it should still be SPD. > > More interestingly is that it does not fail immediately (i.e. the first > time it’s used in SLEPc solvers), > but only on the 4th step. So 3 times SLEPc worked just fine to solve GHEP > with Gamg and zero shift. > Then I think it is not doing what you suppose. I am not inclined to believe that it behaves differently on the same matrix. Matt > Regards, > Denis. > > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
