[petsc-users] MINRES accuracy for a SPD matrix

[Jed Brown]

Are you saying that the MINRES error is larger than CG error?  In which
norm?  And which norm are you using for CG?  (Output from
-ksp_monitor_true_residual -ksp_view would be useful.)

CG does find a solution that is optimal in a different inner product,
though this is usually pretty benign unless you have a poor
preconditioner.

Mohammad Gohardoust via petsc-users <petsc-users at mcs.anl.gov> writes:

> Hi,
>
> I am trying to evaluate different solver/preconditioner combinations for
> solving Richards' equation in porous media. The coefficient matrix is
> symmetric positive definite and is usually solved by CG solver. I tried
> MINRES with various preconditioners. The solution is acceptable but with
> somehow considerable errors (compared to other solvers) which requires me
> to decrease the tolerance threshold in my Picard iteration leading to
> larger computation time. I would like to know if this is common for MINRES
> and how to possibly overcome this?
>
> Thanks,
> Mohammad