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# PCGASMGetSubdomains
Gets the subdomains supported on this MPI rank for the `PCGASM` additive Schwarz preconditioner. 
## Synopsis
```
#include "petscpc.h" 
PetscErrorCode PCGASMGetSubdomains(PC pc, PetscInt *n, IS *iis[], IS *ois[])
```
Not Collective


## Input Parameter

- ***pc -*** the preconditioner context



## Output Parameters

- ***n   -*** the number of subdomains for this MPI rank (default value = 1)
- ***iis -*** the index sets that define the inner subdomains (without overlap) supported on this rank (can be `NULL`)
- ***ois -*** the index sets that define the outer subdomains (with overlap) supported on this rank (can be `NULL`)





## Notes
The user is responsible for destroying the `IS`s and freeing the returned arrays, this can be done with
`PCGASMDestroySubdomains()`

The `IS` numbering is in the parallel, global numbering of the vector.


## See Also
 `PCGASM`, `PCGASMSetOverlap()`, `PCGASMGetSubKSP()`, `PCGASMCreateSubdomains2D()`,
`PCGASMSetSubdomains()`, `PCGASMGetSubmatrices()`, `PCGASMDestroySubdomains()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/gasm/gasm.c.html#PCGASMGetSubdomains">src/ksp/pc/impls/gasm/gasm.c</A>


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


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