# PetscLayoutReference
Causes a PETSc `Vec` or `Mat` to share a `PetscLayout` with one that already exists. 
## Synopsis
```
#include "petscis.h" 
PetscErrorCode PetscLayoutReference(PetscLayout in, PetscLayout *out)
```
Collective on in


## Input Parameter

- ***in -*** input `PetscLayout` to be copied



## Output Parameter

- ***out -*** the reference location





## Notes
`PetscLayoutSetUp()` does not need to be called on the resulting `PetscLayout`

If the out location already contains a `PetscLayout` it is destroyed


## See Also
 [PetscLayout](sec_matlayout), `PetscLayoutCreate()`, `PetscLayoutDestroy()`, `PetscLayoutSetUp()`, `PetscLayoutDuplicate()`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/utils/pmap.c.html#PetscLayoutReference">src/vec/is/utils/pmap.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/vec/is/utils/pmap.c)


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