PETSc version 3.16.5
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# PCShellSetPreSolve

Sets routine to apply to the operators/vectors before a KSPSolve() is applied. This usually does something like scale the linear system in some application specific way.

### Synopsis

    #include "petscpc.h"
    PetscErrorCode  PCShellSetPreSolve(PC pc,PetscErrorCode (*presolve)(PC,KSP,Vec,Vec))

Logically Collective on PC

### Input Parameters

| pc | - the preconditioner context
| presolve | - the application-provided presolve routine

### Calling sequence of presolve

       PetscErrorCode presolve (PC,KSP ksp,Vec b,Vec x)

| pc | - the preconditioner, get the application context with PCShellGetContext()
| xin | - input vector
| xout | - output vector

### Notes

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

### See Also

PCShellSetApplyRichardson(), PCShellSetSetUp(), PCShellSetApplyTranspose(), PCShellSetPostSolve(), PCShellSetContext()

### Level

developer

### Location

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

### Implementations

PCShellSetPreSolve_Shell(PC pc,PetscErrorCode (*presolve) in src/ksp/pc/impls/shell/shellpc.c
Index of all PC routines
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