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. Thanks in advance, Eduardo
