# PetscDualSpaceGetHeightSubspace
Get the subset of the dual space basis that is supported on a mesh point of a given height.  This assumes that the reference cell is symmetric over points of this height. 
## Synopsis
```
#include "petscfe.h" 
PetscErrorCode PetscDualSpaceGetHeightSubspace(PetscDualSpace sp, PetscInt height, PetscDualSpace *subsp)
```
Not collective


## Input Parameters

- ***sp -*** the `PetscDualSpace` object
- ***height -*** the height of the mesh point for which the subspace is desired



## Output Parameter

- ***subsp -*** the subspace.  Note that the functionals in the subspace are with respect to the intrinsic geometry of the
point, which will be of lesser dimension if height > 0.





## Notes
If the dual space is not defined on mesh points of the given height (e.g. if the space is discontinuous and
pointwise values are not defined on the element boundaries), or if the implementation of `PetscDualSpace` does not
support extracting subspaces, then NULL is returned.

This does not increment the reference count on the returned dual space, and the user should not destroy it.


## See Also
 `PetscDualSpace`, `PetscSpaceGetHeightSubspace()`, `PetscDualSpace`, `PetscDualSpaceGetPointSubspace()`

## Level
advanced

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


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


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