KSPFGMRES#
Implements the Flexible Generalized Minimal Residual method. Flexible Krylov Methods
Options Database Keys#
-ksp_gmres_restart
- the number of Krylov directions to orthogonalize against-ksp_gmres_haptol
- 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.
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 PCJACOBI
Developer Note#
This object is subclassed off of KSPGMRES, see the source code in src/ksp/ksp/impls/gmres for comments on the structure of the code
Contributed by#
Allison Baker
See Also#
KSP: Linear System Solvers, Flexible Krylov Methods, KSPCreate(), KSPSetType(), KSPType, KSP, KSPGMRES, KSPLGMRES,
KSPGMRESSetRestart(), KSPGMRESSetHapTol(), KSPGMRESSetPreAllocateVectors(), KSPGMRESSetOrthogonalization(), KSPGMRESGetOrthogonalization(),
KSPGMRESClassicalGramSchmidtOrthogonalization(), KSPGMRESModifiedGramSchmidtOrthogonalization(),
KSPGMRESCGSRefinementType, KSPGMRESSetCGSRefinementType(), KSPGMRESGetCGSRefinementType(), KSPGMRESMonitorKrylov(), KSPFGMRESSetModifyPC(),
KSPFGMRESModifyPCKSP()
Level#
beginner
Location#
Examples#
src/ksp/pc/tutorials/ex4.c
src/dm/impls/stag/tutorials/ex8.c
src/ts/tutorials/ex30.c
src/dm/impls/stag/tutorials/ex2.c
src/dm/impls/stag/tutorials/ex3.c
src/ksp/ksp/tutorials/ex7.c
src/dm/impls/stag/tutorials/ex4.c
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages