petsc-3.14.5 2021-03-03
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# KSPPREONLY

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

### Options Database Keys

| -ksp_type preonly

### Notes

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

### Developer Notes

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

KSPCreate(), KSPSetType(), KSPType, KSP, KSPRICHARDSON, KSPCHEBYSHEV

### Level

beginner

### Location

src/ksp/ksp/impls/preonly/preonly.c

### Examples

src/ksp/ksp/tutorials/ex52.c.html
src/ksp/ksp/tutorials/ex78.c.html
src/ksp/ksp/tutorials/ex52f.F90.html
src/tao/constrained/tutorials/maros.c.html
src/tao/constrained/tutorials/toy.c.html
src/tao/constrained/tutorials/ex1.c.html
src/tao/constrained/tutorials/toyf.F90.html
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages