I am solving a FEM solid mechanics linear elasticity model, for now the only problem is the mesh that has needle-shaped and very flat elements. Have you any suggestion of preconditioner (and references). Thanks, Eduardo
On Tue, Jun 2, 2015 at 4:11 AM, Barry Smith <[email protected]> wrote: > > > On Jun 1, 2015, at 4:06 PM, Eduardo <[email protected]> wrote: > > > > I am solving a linear system for which the preconditioned residual > decreases, but the true residual increases (or have an erratic behavior). > According to Petsc FAQ, this is due to a preconditioner that is singular or > close to singular. What can I do in this case? I used GMRES with ILU > preconditioner. > ^^^^^^^^^^^^^^^ > > > > Incidentally, I tried to solve a smaller system with a direct solver > (superlu_dist) and it ran, so the system apparently is not singular. > > ILU can produce very badly conditioned (one could say singular > PRECONDITIONER) from not singular sparse matrices. So it doesn't have > anything to do with the system itself being singular. > > What type of problem are you solving? Different problems need different > preconditioners. > > Barry > > > > > > > Thanks in advance, > > Eduardo > >
