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# DMPlexGetOrdering
Calculate a reordering of the mesh 
## Synopsis
```
#include "petscdmplex.h"   
#include "petscmat.h"      
PetscErrorCode DMPlexGetOrdering(DM dm, MatOrderingType otype, DMLabel label, IS *perm)
```
Collective


## Input Parameters

- ***dm -*** The DMPlex object
- ***otype -*** type of reordering, see `MatOrderingType`
- ***label -*** [Optional] Label used to segregate ordering into sets, or `NULL`



## Output Parameter

- ***perm -*** The point permutation as an `IS`, `perm`[old point number] = new point number





## Note
The label is used to group sets of points together by label value. This makes it easy to reorder a mesh which
has different types of cells, and then loop over each set of reordered cells for assembly.


## See Also
 `DMPLEX`, `DMPlexPermute()`, `MatOrderingType`, `MatGetOrdering()`

## Level
intermediate

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


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