# DMSetNullSpaceConstructor
Provide a callback function which constructs the nullspace for a given field, defined with `DMAddField()`, when function spaces are joined or split, such as in `DMCreateSubDM()` 
## Synopsis
```
#include "petscdm.h"          
#include "petscdmlabel.h"     
#include "petscds.h"     
PetscErrorCode DMSetNullSpaceConstructor(DM dm, PetscInt field, PetscErrorCode (*nullsp)(DM, PetscInt, PetscInt, MatNullSpace *))
```
Logically collective on dm


## Input Parameters

- ***dm     -*** The `DM`
- ***field  -*** The field number for the nullspace
- ***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 Notes
This function is not available from Fortran.


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

## Level
intermediate

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

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex62.c.html">src/snes/tutorials/ex62.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex69.c.html">src/snes/tutorials/ex69.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex76.c.html">src/snes/tutorials/ex76.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ts/tutorials/ex76.c.html">src/ts/tutorials/ex76.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ts/tutorials/ex77.c.html">src/ts/tutorials/ex77.c.html</A><BR>


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