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# 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


## 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 `-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>


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


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