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 KSPNONE.
Options Database Keys#
-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
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.