| -ksp_gmres_restart <restart> | - the number of Krylov directions to orthogonalize against | |
| -ksp_gmres_haptol <tol> | - sets the tolerance for "happy ending" (exact convergence) | |
| -ksp_gmres_preallocate | - preallocate all the Krylov search directions initially (otherwise groups of vectors are allocated as needed) | |
| -ksp_gmres_classicalgramschmidt | - use classical (unmodified) Gram-Schmidt to orthogonalize against the Krylov space (fast) (the default) | |
| -ksp_gmres_modifiedgramschmidt | - use modified Gram-Schmidt in the orthogonalization (more stable, but slower) | |
| -ksp_gmres_cgs_refinement_type <never,ifneeded,always> | - determine if iterative refinement is used to increase the stability of the classical Gram-Schmidt orthogonalization. | |
| -ksp_gmres_krylov_monitor | - plot the Krylov space generated |
Notes: Left and right preconditioning are supported, but not symmetric preconditioning.