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# PCSetDiagonalScale
Indicates the left scaling to use to apply an additional left and right scaling as needed by certain time-stepping codes. 
## Synopsis
```
#include "petscksp.h" 
PetscErrorCode PCSetDiagonalScale(PC pc, Vec s)
```
Logically Collective


## Input Parameters

- ***pc -*** the preconditioner context
- ***s -*** scaling vector





## Notes
The system solved via the Krylov method is
```none
           D M A D^{-1} y = D M b  for left preconditioning or
           D A M D^{-1} z = D b for right preconditioning
```


`PCDiagonalScaleLeft()` scales a vector by D. `PCDiagonalScaleRight()` scales a vector by D^{-1}.


## See Also
 `PCCreate()`, `PCSetUp()`, `PCDiagonalScaleLeft()`, `PCDiagonalScaleRight()`, `PCGetDiagonalScale()`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/interface/precon.c.html#PCSetDiagonalScale">src/ksp/pc/interface/precon.c</A>


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


[Index of all PC routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)