petsc-3.7.7 2017-09-25
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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.

### Keywords

PC, shell, set, apply, user-provided

### See Also

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

Level:developer
Location:src/ksp/pc/impls/shell/shellpc.c
Index of all PC routines
Table of Contents for all manual pages
Index of all manual pages