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# KSPFGMRES

Implements the Flexible Generalized Minimal Residual method. developed by Saad with restart

### Options Database Keys

| -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 <refine_never,refine_ifneeded,refine_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
| -ksp_fgmres_modifypcnochange | - do not change the preconditioner between iterations
| -ksp_fgmres_modifypcksp | - modify the preconditioner using KSPFGMRESModifyPCKSP()

### Notes

See KSPFGMRESSetModifyPC() for how to vary the preconditioner between iterations Only right preconditioning is supported.

### Notes

The following options -ksp_type fgmres -pc_type ksp -ksp_ksp_type bcgs -ksp_view -ksp_pc_type jacobi make the preconditioner (or inner solver) be bi-CG-stab with a preconditioner of Jacobi.

### Developer Notes

This object is subclassed off of KSPGMRES

### See Also

KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPGMRES, KSPLGMRES,
KSPGMRESSetRestart(), KSPGMRESSetHapTol(), KSPGMRESSetPreAllocateVectors(), KSPGMRESSetOrthogonalization(), KSPGMRESGetOrthogonalization(), KSPGMRESClassicalGramSchmidtOrthogonalization(), KSPGMRESModifiedGramSchmidtOrthogonalization(), KSPGMRESCGSRefinementType, KSPGMRESSetCGSRefinementType(), KSPGMRESGetCGSRefinementType(), KSPGMRESMonitorKrylov(), KSPFGMRESSetModifyPC(), KSPFGMRESModifyPCKSP()

### Level

beginner

### Location

src/ksp/ksp/impls/gmres/fgmres/fgmres.c

### Examples

src/dm/impls/stag/tutorials/ex2.c.html
src/dm/impls/stag/tutorials/ex3.c.html
src/dm/impls/stag/tutorials/ex4.c.html
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages