# PCEisenstatSetOmega
Sets the SSOR relaxation coefficient, omega, to use with Eisenstat's trick (where omega = 1.0 by default) 
## Synopsis
```
#include "petscpc.h" 
PetscErrorCode PCEisenstatSetOmega(PC pc, PetscReal omega)
```
Logically Collective on pc


## Input Parameters

- ***pc -*** the preconditioner context
- ***omega -*** relaxation coefficient (0 < omega < 2)



## Options Database Key

- ***-pc_eisenstat_omega <omega> -*** Sets omega



## Notes
The Eisenstat trick implementation of SSOR requires about 50% of the
usual amount of floating point operations used for SSOR + Krylov method;
however, the preconditioned problem must be solved with both left
and right preconditioning.

To use SSOR without the Eisenstat trick, employ the `PCSOR` preconditioner,
which can be chosen with the database options
```none
-pc_type  sor  -pc_sor_symmetric
```




## See Also
 `PCSORSetOmega()`, `PCEISENSTAT`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/eisens/eisen.c.html#PCEisenstatSetOmega">src/ksp/pc/impls/eisens/eisen.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/eisens/eisen.c.html#PCEisenstatSetOmega_Eisenstat">PCEisenstatSetOmega_Eisenstat in src/ksp/pc/impls/eisens/eisen.c</A><BR>


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


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