:orphan:
# VecScatterBegin
Begins a generalized scatter from one vector to another. Complete the scattering phase with `VecScatterEnd()`. 
## Synopsis
```
#include "petscsf.h" 
PetscErrorCode VecScatterBegin(VecScatter sf, Vec x, Vec y, InsertMode addv, ScatterMode mode)
```
Neighbor-wise Collective


## Input Parameters

- ***sf -*** scatter context generated by `VecScatterCreate()`
- ***x -*** the vector from which we scatter
- ***y -*** the vector to which we scatter
- ***addv -*** either `ADD_VALUES`, `MAX_VALUES`, `MIN_VALUES` or `INSERT_VALUES`, with `INSERT_VALUES` mode any location
not scattered to retains its old value; i.e. the vector is NOT first zeroed.
- ***mode -*** the scattering mode, usually `SCATTER_FORWARD`.  The available modes are: `SCATTER_FORWARD` or `SCATTER_REVERSE`





## Notes
The vectors `x` and `y` need not be the same vectors used in the call
to `VecScatterCreate()`, but `x` must have the same parallel data layout
as that passed in as the `x` to `VecScatterCreate()`, similarly for the `y`.
Most likely they have been obtained from `VecDuplicate()`.

You cannot change the values in the input vector between the calls to `VecScatterBegin()`
and `VecScatterEnd()`.

If you use `SCATTER_REVERSE` the two arguments `x` and `y` should be reversed, from
the `SCATTER_FORWARD`.

y[iy[i]] = x[ix[i]], for i=0,...,ni-1

This scatter is far more general than the conventional
scatter, since it can be a gather or a scatter or a combination,
depending on the indices ix and iy.  If x is a parallel vector and y
is sequential, `VecScatterBegin()` can serve to gather values to a
single processor.  Similarly, if `y` is parallel and `x` sequential, the
routine can scatter from one processor to many processors.


## See Also
 [](sec_scatter), `VecScatter`, `VecScatterCreate()`, `VecScatterEnd()`

## Level
intermediate

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

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/tutorials/ex14.c.html">src/dm/tutorials/ex14.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/tutorials/ex22.c.html">src/dm/tutorials/ex22.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/tutorials/ex25.c.html">src/dm/tutorials/ex25.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/tutorials/ex6.c.html">src/dm/tutorials/ex6.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex43.c.html">src/ksp/ksp/tutorials/ex43.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex49.c.html">src/ksp/ksp/tutorials/ex49.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex73.c.html">src/ksp/ksp/tutorials/ex73.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/tao/constrained/tutorials/ex1.c.html">src/tao/constrained/tutorials/ex1.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/tao/pde_constrained/tutorials/elliptic.c.html">src/tao/pde_constrained/tutorials/elliptic.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/tao/pde_constrained/tutorials/hyperbolic.c.html">src/tao/pde_constrained/tutorials/hyperbolic.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/tao/pde_constrained/tutorials/parabolic.c.html">src/tao/pde_constrained/tutorials/parabolic.c</A><BR>


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


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