[petsc-users] Convergence of iterative linear solver

[Eduardo]

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
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