# DMGetNullSpaceConstructor
Return the callback function which constructs the nullspace for a given field, defined with `DMAddField()` 
## Synopsis
```
#include "petscdm.h"          
#include "petscdmlabel.h"     
#include "petscds.h"     
PetscErrorCode DMGetNullSpaceConstructor(DM dm, PetscInt field, PetscErrorCode (**nullsp)(DM, PetscInt, PetscInt, MatNullSpace *))
```
Not collective


## Input Parameters

- ***dm     -*** The `DM`
- ***field  -*** The field number for the nullspace



## Output Parameter

- ***nullsp -*** A callback to create the nullspace



## Calling sequence of nullsp
```none
    PetscErrorCode nullsp(DM dm, PetscInt origField, PetscInt field, MatNullSpace *nullSpace)
```


- ***dm        -*** The present DM
- ***origField -*** The field number given above, in the original DM
- ***field     -*** The field number in dm
- ***nullSpace -*** The nullspace for the given field



## Fortran Note
This function is not available from Fortran.




## See Also
 `DMAddField()`, `DMGetField()`, `DMSetNullSpaceConstructor()`, `DMSetNearNullSpaceConstructor()`, `DMGetNearNullSpaceConstructor()`, `DMCreateSubDM()`, `DMCreateSuperDM()`

## Level
intermediate

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


---
[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](/docs/manualpages/index.md)  
[Index of all manual pages](/docs/manualpages/singleindex.md)  
