# PetscCommSplitReductionBegin
Begin an asynchronous split-mode reduction 
## Synopsis
```
#include "petscvec.h"    
PetscErrorCode PetscCommSplitReductionBegin(MPI_Comm comm)
```
Collective but not synchronizing


## Input Parameter
comm - communicator on which split reduction has been queued




## Note
Calling this function is optional when using split-mode reduction. On supporting hardware, calling this after all
VecXxxBegin() allows the reduction to make asynchronous progress before the result is needed (in VecXxxEnd()).


## See Also
 `VecNormBegin()`, `VecNormEnd()`, `VecDotBegin()`, `VecDotEnd()`, `VecTDotBegin()`, `VecTDotEnd()`, `VecMDotBegin()`, `VecMDotEnd()`, `VecMTDotBegin()`, `VecMTDotEnd()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/vec/utils/comb.c.html#PetscCommSplitReductionBegin">src/vec/vec/utils/comb.c</A>


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


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