petsc-3.14.5 2021-03-03
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# KSP_GMRES_CGS_REFINE_IFNEEDED

Do the classical (unmodified) Gram-Schmidt process and one step of iterative refinement if an estimate of the orthogonality of the resulting vectors indicates poor orthogonality.

Note: This is slower than KSP_GMRES_CGS_REFINE_NEVER because it requires an extra norm computation to estimate the orthogonality but is more stable.

### See Also

KSPGMRESClassicalGramSchmidtOrthogonalization(), KSPGMRESSetOrthogonalization(), KSPGMRESGetOrthogonalization(),
KSPGMRESSetCGSRefinementType(), KSPGMRESGetCGSRefinementType(), KSP_GMRES_CGS_REFINE_NEVER, KSP_GMRES_CGS_REFINE_ALWAYS, KSPGMRESModifiedGramSchmidtOrthogonalization()

### Level

advanced

### Location

src/ksp/ksp/guess/../../../../include/petscksp.h
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages