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# DMGlobalToLocalHookAdd
adds a callback to be run when `DMGlobalToLocal()` is called 
## Synopsis
```
#include "petscdm.h"          
#include "petscdmlabel.h"     
#include "petscds.h"     
PetscErrorCode DMGlobalToLocalHookAdd(DM dm, PetscErrorCode (*beginhook)(DM, Vec, InsertMode, Vec, void *), PetscErrorCode (*endhook)(DM, Vec, InsertMode, Vec, void *), void *ctx)
```
Logically Collective


## Input Parameters

- ***dm -*** the `DM`
- ***beginhook -*** function to run at the beginning of `DMGlobalToLocalBegin()`
- ***endhook -*** function to run after `DMGlobalToLocalEnd()` has completed
- ***ctx -*** [optional] user-defined context for provide data for the hooks (may be `NULL`)



## Calling sequence of `beginhook`
```none
PetscErrorCode  beginhook(DM fine, VecScatter out, VecScatter in, DM coarse, void *ctx)
```

- ***dm -*** global DM
- ***g -*** global vector
- ***mode -*** mode
- ***l -*** local vector
- ***ctx -*** optional user-defined function context



## Calling sequence of `endhook`
```none
PetscErrorCode  endhook(DM fine, VecScatter out, VecScatter in, DM coarse, void *ctx)
```

- ***global -*** global DM
- ***ctx -*** optional user-defined function context





## Note
The hook may be used to provide, for example, values that represent boundary conditions in the local vectors that do not exist on the global vector.


## See Also
 [](ch_dmbase), `DM`, `DMGlobalToLocal()`, `DMRefineHookAdd()`, `SNESFASGetInterpolation()`, `SNESFASGetInjection()`, `PetscObjectCompose()`, `PetscContainerCreate()`

## Level
advanced

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


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