:orphan:
# DMCreateInjection
Gets injection matrix between two `DM` objects. This is an operator that applied to a vector obtained with `DMCreateGlobalVector()` on the fine grid maps the values to a vector on the vector on the coarse `DM` by simply selecting the values on the coarse grid points. This compares to the operator obtained by `DMCreateRestriction()` or the transpose of the operator obtained by `DMCreateInterpolation()` that uses a "local weighted average" of the values around the coarse grid point as the coarse grid value. 
## Synopsis
```
#include "petscdm.h"          
#include "petscdmlabel.h"     
#include "petscds.h"     
PetscErrorCode DMCreateInjection(DM dac, DM daf, Mat *mat)
```
Collective


## Input Parameters

- ***dac -*** the `DM` object
- ***daf -*** the second, finer `DM` object



## Output Parameter

- ***mat -*** the injection





## Note
For `DMDA` objects this only works for "uniform refinement", that is the refined mesh was obtained `DMRefine()` or the coarse mesh was obtained by
`DMCoarsen()`. The coordinates set into the `DMDA` are completely ignored in computing the injection.


## See Also
 [](ch_dmbase), `DM`, `DMDestroy()`, `DMView()`, `DMCreateGlobalVector()`, `DMCreateColoring()`, `DMCreateMatrix()`, `DMCreateMassMatrix()`, `DMCreateInterpolation()`,
`DMCreateRestriction()`, `MatRestrict()`, `MatInterpolate()`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/interface/dm.c.html#DMCreateInjection">src/dm/interface/dm.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/da/dainterp.c.html#DMCreateInjection_DA">DMCreateInjection_DA in src/dm/impls/da/dainterp.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/forest/p4est/pforest.h.html#DMCreateInjection_pforest">DMCreateInjection_pforest in src/dm/impls/forest/p4est/pforest.h</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/moab/dmmbmg.cxx.html#DMCreateInjection_Moab">DMCreateInjection_Moab in src/dm/impls/moab/dmmbmg.cxx</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/plex/plex.c.html#DMCreateInjection_Plex">DMCreateInjection_Plex in src/dm/impls/plex/plex.c</A><BR>


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


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