# PetscSFGatherBegin
begin pointwise gather of all leaves into multi-roots, to be completed with `PetscSFGatherEnd()` 
## Synopsis
```
#include "petscsf.h" 
PetscErrorCode PetscSFGatherBegin(PetscSF sf, MPI_Datatype unit, const void *leafdata, void *multirootdata)
```
Collective


## Input Parameters

- ***sf -*** star forest
- ***unit -*** data type
- ***leafdata -*** leaf data to gather to roots



## Output Parameter

- ***multirootdata -*** root buffer to gather into, amount of space per root is equal to its degree





## See Also
 `PetscSF`, `PetscSFComputeDegreeBegin()`, `PetscSFScatterBegin()`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/sf/interface/sf.c.html#PetscSFGatherBegin">src/vec/is/sf/interface/sf.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/sf/tutorials/ex1.c.html">src/vec/is/sf/tutorials/ex1.c.html</A><BR>


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


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