: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
src/dm/impls/plex/plexsubmesh.c
## Examples
src/snes/tutorials/ex12.c
src/snes/tutorials/ex56.c
src/snes/tutorials/ex77.c
src/tao/tutorials/ex3.c
src/ts/tutorials/ex48.c
## Implementations
DMPlexMarkBoundaryFaces_Internal in src/dm/impls/plex/plexsubmesh.c
---
[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)