:orphan:
# DMPlexMarkBoundaryFaces
Mark all faces on the boundary 
## Synopsis
```
#include "petscdmplex.h"    
#include "petscdmlabel.h"   
PetscErrorCode DMPlexMarkBoundaryFaces(DM dm, PetscInt val, DMLabel label)
```
Not Collective


## Input Parameters

- ***dm -*** The original `DM`
- ***val -*** The marker value, or `PETSC_DETERMINE` to use some value in the closure (or 1 if none are found)



## Output Parameter

- ***label -*** The `DMLabel` marking boundary faces with the given value





## Note
This function will use the point `PetscSF` from the input `DM` to exclude points on the partition boundary from being marked, unless the partition overlap is greater than zero. If you also wish to mark the partition boundary, you can use `DMSetPointSF()` to temporarily set it to `NULL`, and then reset it to the original object after the call.


## See Also
 [](ch_unstructured), `DM`, `DMPLEX`, `DMLabelCreate()`, `DMCreateLabel()`

## Level
developer

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

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex12.c.html">src/snes/tutorials/ex12.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex56.c.html">src/snes/tutorials/ex56.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex77.c.html">src/snes/tutorials/ex77.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/tao/tutorials/ex3.c.html">src/tao/tutorials/ex3.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ts/tutorials/ex48.c.html">src/ts/tutorials/ex48.c</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/plex/plexsubmesh.c.html#DMPlexMarkBoundaryFaces_Internal">DMPlexMarkBoundaryFaces_Internal in src/dm/impls/plex/plexsubmesh.c</A><BR>


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