From: Roy Stogner <roystgnr@ic...>  20070625 23:25:44

On Mon, 25 Jun 2007, pcorreia@... wrote: > The result I get is: > ERROR: LASPACK Error: > in ILUFactor for Mat: > Factorization produces zero pivot elements. > [0] src/numerics/laspack_linear_solver.C, line 274, compiled Jun 15 2007 > I suppose this has to do with the sparsity pattern defined by the dof_map > object. Not necessarily. If your matrix is singular (say, Stokes flow with no pinned pressure value) it might give you a system that behaves will in iterative methods but breaks factorizing preconditioners. > The question is: how to define a special sparsity pattern which would take > in account the degrees of freedom on two neighbor elements. I've never really looked at the compute_sparsity_pattern code, but there is an option there (turned on by the command line option "implicit_neighbor_dofs) that appears to be adding additional connectivity between neighboring element degrees of freedom. Give that a try.  Roy 