KSPPREONLY#
This implements a method that applies ONLY the preconditioner exactly once. It is commonly used with the direct solver preconditioners like PCLU and PCCHOLESKY, but it may also be used when a single iteration of the
preconditioner is needed for smoothing in multigrid, PCMG or PCGAMG or within some other nested linear solve such as PCFIELDSPLIT or PCBJACOBI.
There is an alias of this with the name KSPNONE.
Options Database Key#
-ksp_type preonly - use a single application of the preconditioner only
Notes#
Since this does not involve an iteration the basic KSP parameters such as tolerances and maximum iteration counts
do not apply
To apply the preconditioner multiple times 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, PCRedistributeGetKSP(), KSPNONE
Level#
beginner
Location#
Examples#
src/ksp/ksp/tutorials/ex57f.F90
src/ksp/ksp/tutorials/ex52.c
src/snes/tutorials/ex31.c
src/tao/constrained/tutorials/maros.c
src/tao/constrained/tutorials/ex1.c
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages