:orphan:
# PCShellSetApplySymmetricLeft
Sets routine to use as left preconditioner (when the `PC_SYMMETRIC` is used). 
## Synopsis
```
#include "petscpc.h" 
PetscErrorCode PCShellSetApplySymmetricLeft(PC pc, PetscErrorCode (*apply)(PC, Vec, Vec))
```
Logically Collective


## Input Parameters

- ***pc -*** the preconditioner context
- ***apply -*** the application-provided left preconditioning routine



## Calling sequence of `apply`
```none
   PetscErrorCode apply(PC pc, Vec xin, Vec xout)
```


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





## See Also
 `PCSHELL`, `PCShellSetApply()`, `PCShellSetApplySymmetricLeft()`, `PCShellSetSetUp()`, `PCShellSetApplyTranspose()`, `PCShellSetContext()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/shell/shellpc.c.html#PCShellSetApplySymmetricLeft">src/ksp/pc/impls/shell/shellpc.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/shell/shellpc.c.html#PCShellSetApplySymmetricLeft_Shell(PC pc, PetscErrorCode (*apply)">PCShellSetApplySymmetricLeft_Shell(PC pc, PetscErrorCode (*apply) in src/ksp/pc/impls/shell/shellpc.c</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/pc/impls/shell/shellpc.c)


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