PETSc version 3.16.5
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# PCShellSetApplyRichardson

Sets routine to use as preconditioner in Richardson iteration.

### Synopsis

    #include "petscpc.h"
    PetscErrorCode  PCShellSetApplyRichardson(PC pc,PetscErrorCode (*apply)(PC,Vec,Vec,Vec,PetscReal,PetscReal,PetscReal,PetscInt,PetscBool,PetscInt*,PCRichardsonConvergedReason*))

Logically Collective on PC

### Input Parameters

| pc | - the preconditioner context
| apply | - the application-provided preconditioning routine

### Calling sequence of apply

       PetscErrorCode apply (PC pc,Vec b,Vec x,Vec r,PetscReal rtol,PetscReal abstol,PetscReal dtol,PetscInt maxits)

| pc | - the preconditioner, get the application context with PCShellGetContext()
| b | - right-hand-side
| x | - current iterate
| r | - work space
| rtol | - relative tolerance of residual norm to stop at
| abstol | - absolute tolerance of residual norm to stop at
| dtol | - if residual norm increases by this factor than return
| maxits | - number of iterations to run

### Notes

the function MUST return an error code of 0 on success and nonzero on failure.

### See Also

PCShellSetApply(), PCShellSetContext()

### Level

developer

### Location

src/ksp/pc/impls/shell/shellpc.c

### Implementations

PCShellSetApplyRichardson_Shell(PC pc,PetscErrorCode (*applyrich) in src/ksp/pc/impls/shell/shellpc.c
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