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

### Notes

By default the GASM preconditioner uses 1 subdomain per processor. To use
multiple subdomain per perocessor or "straddling" subdomains that intersect
multiple processors 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 GASM
variant that is equivalent to the block Jacobi preconditioner.

Note that 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

PCGASMSetSubdomains(), PCGASMGetSubKSP(),

PCGASMCreateSubdomains2D(), PCGASMGetSubdomains()

### Level

intermediate

### Location

src/ksp/pc/impls/gasm/gasm.c
### Examples

src/ksp/ksp/examples/tutorials/ex62.c.html

### Implementations

PCGASMSetOverlap_GASM in src/ksp/pc/impls/gasm/gasm.c

Index of all PC routines

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