:orphan:
# PCGASMSetOverlap
Sets the overlap between a pair of subdomains for the additive Schwarz preconditioner `PCGASM`.  Either all or no MPI ranks in the pc communicator must call this routine. 
## Synopsis
```
#include "petscpc.h" 
PetscErrorCode PCGASMSetOverlap(PC pc, PetscInt ovl)
```
Logically Collective


## Input Parameters

- ***pc  -*** the preconditioner context
- ***ovl -*** the amount of overlap between subdomains (ovl >= 0, default value = 0)



## Options Database Key

- ***-pc_gasm_overlap <overlap> -*** Sets overlap





## Notes
By default the `PCGASM` preconditioner uses 1 subdomain per rank.  To use
multiple subdomain per perocessor or "straddling" subdomains that intersect
multiple ranks use `PCGASMSetSubdomains()` (or option `-pc_gasm_total_subdomains` <n>).

The overlap defaults to 0, so if one desires that no additional
overlap be computed beyond what may have been set with a call to
`PCGASMSetSubdomains()`, then `ovl` must be set to be 0.  In particular, if one does
not explicitly set the subdomains in application code, then all overlap would be computed
internally by PETSc, and using an overlap of 0 would result in an `PCGASM`
variant that is equivalent to the block Jacobi preconditioner.

One can define initial index sets with any overlap via
`PCGASMSetSubdomains()`; the routine `PCGASMSetOverlap()` merely allows
PETSc to extend that overlap further, if desired.


## See Also
 `PCGASM`, `PCGASMSetSubdomains()`, `PCGASMGetSubKSP()`,
`PCGASMCreateSubdomains2D()`, `PCGASMGetSubdomains()`

## Level
intermediate

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

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex62.c.html">src/ksp/ksp/tutorials/ex62.c</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/gasm/gasm.c.html#PCGASMSetOverlap_GASM">PCGASMSetOverlap_GASM in src/ksp/pc/impls/gasm/gasm.c</A><BR>


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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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