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# DMCreateNeumannOverlap
Generates an IS, an unassembled (Neumann) Mat, a setup function, and the corresponding context to be used by PCHPDDM. 
## Synopsis
```
#include "petscdmplex.h"   
PetscErrorCode DMCreateNeumannOverlap_Plex(DM dm, IS *ovl, Mat *J, PetscErrorCode (**setup)(Mat, PetscReal, Vec, Vec, PetscReal, IS, void *), void **setup_ctx)
```

## Input Parameter

- ***dm -*** preconditioner context



## Output Parameters

- ***ovl -*** index set of overlapping subdomains
- ***J -*** unassembled (Neumann) local matrix
- ***setup -*** function for generating the matrix
- ***setup_ctx -*** context for setup



## Options Database Keys

- ***-dm_plex_view_neumann_original -*** view the DM without overlap
- ***-dm_plex_view_neumann_overlap -*** view the DM with overlap as needed by PCHPDDM





## See Also
 `DMCreate()`, `DM`, `MATIS`, `PCHPDDM`, `PCHPDDMSetAuxiliaryMat()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/plex/plexhpddm.c.html#DMCreateNeumannOverlap">src/dm/impls/plex/plexhpddm.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/forest/p4est/pforest.h.html#DMCreateNeumannOverlap_pforest(DM dm, IS *ovl, Mat *J, PetscErrorCode (**setup)">DMCreateNeumannOverlap_pforest(DM dm, IS *ovl, Mat *J, PetscErrorCode (**setup) in src/dm/impls/forest/p4est/pforest.h</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/plex/plexhpddm.c.html#DMCreateNeumannOverlap_Plex(DM dm, IS *ovl, Mat *J, PetscErrorCode (**setup)">DMCreateNeumannOverlap_Plex(DM dm, IS *ovl, Mat *J, PetscErrorCode (**setup) in src/dm/impls/plex/plexhpddm.c</A><BR>


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


[Index of all DMPlex routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)