# PCMGSetRestriction
Sets the function to be used to restrict dual vectors from level l to l-1. 
## Synopsis
```
#include "petscksp.h" 
PetscErrorCode PCMGSetRestriction(PC pc, PetscInt l, Mat mat)
```
Logically Collective on pc


## Input Parameters

- ***pc -*** the multigrid context
- ***l -*** the level (0 is coarsest) to supply [Do not supply 0]
- ***mat -*** the restriction matrix





## Notes
Usually this is the same matrix used also to set the interpolation
for the same level.

One can pass in the interpolation matrix or its transpose; PETSc figures
out from the matrix size which one it is.

If you do not set this, the transpose of the `Mat` set with `PCMGSetInterpolation()`
is used.


## See Also
 `PCMG`, `PCMGSetInterpolation()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/mg/mgfunc.c.html#PCMGSetRestriction">src/ksp/pc/impls/mg/mgfunc.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/tutorials/ex4.c.html">src/dm/impls/stag/tutorials/ex4.c.html</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/pc/impls/mg/mgfunc.c)


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