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# KSPPGMRES
Implements the Pipelined Generalized Minimal Residual method. [](sec_pipelineksp) 
## 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





## Note
MPI configuration may be necessary for reductions to make asynchronous progress, which is important for performance of pipelined methods.
See [](doc_faq_pipelined)


## Reference
Ghysels, Ashby, Meerbergen, Vanroose, Hiding global communication latencies in the GMRES algorithm on massively parallel machines, 2012.


## Developer Note
This object is subclassed off of `KSPGMRES`


## See Also
 [](ch_ksp), [](sec_pipelineksp), [](doc_faq_pipelined), `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPGMRES`, `KSPLGMRES`, `KSPPIPECG`, `KSPPIPECR`,
`KSPGMRESSetRestart()`, `KSPGMRESSetHapTol()`, `KSPGMRESSetPreAllocateVectors()`, `KSPGMRESSetOrthogonalization()`, `KSPGMRESGetOrthogonalization()`,
`KSPGMRESClassicalGramSchmidtOrthogonalization()`, `KSPGMRESModifiedGramSchmidtOrthogonalization()`,
`KSPGMRESCGSRefinementType`, `KSPGMRESSetCGSRefinementType()`, `KSPGMRESGetCGSRefinementType()`, `KSPGMRESMonitorKrylov()`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/impls/gmres/pgmres/pgmres.c.html#KSPPGMRES">src/ksp/ksp/impls/gmres/pgmres/pgmres.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/ksp/impls/gmres/pgmres/pgmres.c)


[Index of all KSP routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)