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# KSPFETIDPSetPressureOperator
Sets the operator used to set up the pressure preconditioner for the saddle point `KSPFETIDP` solver, 
## Synopsis
```
#include <petscksp.h> 
PetscErrorCode KSPFETIDPSetPressureOperator(KSP ksp, Mat P)
```
Collective


## Input Parameters

- ***ksp -*** the `KSPFETIDP` solver
- ***P -*** the linear operator to be preconditioned, usually the mass matrix.





## Notes
The operator can be either passed in a) monolithic global ordering, b) pressure-only global ordering
or c) interface pressure ordering (if `-ksp_fetidp_pressure_all false`).
In cases b) and c), the pressure ordering of dofs needs to satisfy
pid_1 < pid_2  iff  gid_1 < gid_2
where pid_1 and pid_2 are two different pressure dof numbers and gid_1 and gid_2 the corresponding
id in the monolithic global ordering.


## See Also
 [](ch_ksp), `KSPFETIDP`, `MATIS`, `PCBDDC`, `KSPFETIDPGetInnerBDDC()`, `KSPFETIDPGetInnerKSP()`, `KSPSetOperators()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/impls/fetidp/fetidp.c.html#KSPFETIDPSetPressureOperator">src/ksp/ksp/impls/fetidp/fetidp.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/impls/fetidp/fetidp.c.html#KSPFETIDPSetPressureOperator_FETIDP">KSPFETIDPSetPressureOperator_FETIDP in src/ksp/ksp/impls/fetidp/fetidp.c</A><BR>


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


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