This implements a method that applies ONLY the preconditioner exactly once. This may be used in inner iterations, where it is desired to allow multiple iterations as well as the “0-iteration” case. It is commonly used with the direct solver preconditioners like PCLU and PCCHOLESKY. There is an alias of this with the name KSPNONE.

Options Database Key#

  • -ksp_type preonly - use preconditioner only


Since this does not involve an iteration the basic KSP parameters such as tolerances and iteration counts do not apply

To apply multiple preconditioners in a simple iteration use KSPRICHARDSON

This KSPType cannot be used with the flag -ksp_initial_guess_nonzero or the call KSPSetInitialGuessNonzero() since it simply applies the preconditioner to the given right-hand side during KSPSolve(). Except when the PCType is PCREDISTRIBUTE; in that situation pass the nonzero initial guess flag with -ksp_initial_guess_nonzero or KSPSetInitialGuessNonzero() both to the outer KSP (which is KSPPREONLY) and the inner KSP object obtained with KSPGetPC() followed by PCRedistributedGetKSP() followed by KSPSetInitialGuessNonzero() or the option -redistribute_ksp_initial_guess_nonzero.

Developer Note#

Even though this method does not use any norms, the user is allowed to set the KSPNormType to any value. This is so the users does not have to change KSPNormType options when they switch from other KSP methods to this one.

See Also#

KSP: Linear System Solvers, KSPCreate(), KSPSetType(), KSPType, KSP, KSPRICHARDSON, KSPCHEBYSHEV, KSPGetPC(), KSPSetInitialGuessNonzero(), PCREDISTRIBUTE, PCRedistributedGetKSP()







Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages