# 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(),
KSPGMRESSetCGSRefinementType(), KSP_GMRES_CGS_REFINE_NEVER, KSP_GMRES_CGS_REFINE_ALWAYS, KSPGMRESModifiedGramSchmidtOrthogonalization()

Level:advanced
Location:src/ksp/ksp/../../../include/petscksp.h
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages