# KSPLGMRES

Augments the standard GMRES approximation space with approximation to the error from previous restart cycles.

### 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 <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
| -ksp_lgmres_constant | - Use constant approx. space size
| -ksp_lgmres_augment <n> | - Number of error approximations to augment the Krylov space with

### Described in

A. H. Baker, E.R. Jessup, and T.A. Manteuffel. A technique for accelerating the convergence of restarted GMRES. Submitted to SIAM Journal on Matrix Analysis and Applications. Also available as Technical Report #CU-CS-945-03, University of Colorado, Department of Computer Science, January, 2003.

Notes: This object is subclassed off of KSPGMRES

Contributed by: Allison Baker

### See Also

KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPFGMRES, KSPGMRES,
KSPGMRESSetRestart(), KSPGMRESSetHapTol(), KSPGMRESSetPreAllocateVectors(), KSPGMRESSetOrthogonalization() KSPGMRESClassicalGramSchmidtOrthogonalization(), KSPGMRESModifiedGramSchmidtOrthogonalization(), KSPGMRESCGSRefinementType, KSPGMRESSetCGSRefinementType(), KSPGMRESKrylovMonitor(), KSPLGMRESSetAugDim(), KSPGMRESSetConstant()

Level:beginner
Location:src/ksp/ksp/impls/gmres/lgmres/lgmres.c
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages