**petsc-master 2018-09-17**

# VecScatterBegin

Begins a generalized scatter from one vector to another. Complete the scattering phase with VecScatterEnd().
### Synopsis

#include "petscvec.h"
PetscErrorCode VecScatterBegin(VecScatter ctx,Vec x,Vec y,InsertMode addv,ScatterMode mode)

Neighbor-wise Collective on VecScatter and Vec

### Input Parameters

Options Database: See VecScatterCreate()

### Notes

The vectors x and y need not be the same vectors used in the call
to VecScatterSetData() or VecScatterCreateWithData(), but x must have the same parallel data layout
as that passed in as the x to VecScatterSetData() or VecScatterCreateWithData(), 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

VecScatterCreateWithData(), VecScatterEnd()

### Level

intermediate

### Location

src/vec/vscat/interface/vscatfce.c
### Examples

src/vec/vec/utils/tagger/examples/tutorials/ex1.c.html

src/dm/examples/tutorials/ex2.c.html

src/dm/examples/tutorials/ex6.c.html

src/ksp/ksp/examples/tutorials/ex43.c.html

src/ksp/ksp/examples/tutorials/ex49.c.html

src/tao/pde_constrained/examples/tutorials/elliptic.c.html

src/tao/pde_constrained/examples/tutorials/parabolic.c.html

src/tao/pde_constrained/examples/tutorials/hyperbolic.c.html

### Implementations

VecScatterBegin_SGToSG in src/vec/vscat/impls/seq/seqvscat.c

VecScatterBegin_SGToSS_Stride1 in src/vec/vscat/impls/seq/seqvscat.c

VecScatterBegin_SGToSS in src/vec/vscat/impls/seq/seqvscat.c

VecScatterBegin_SSToSG_Stride1 in src/vec/vscat/impls/seq/seqvscat.c

VecScatterBegin_SSToSG in src/vec/vscat/impls/seq/seqvscat.c

VecScatterBegin_SSToSS in src/vec/vscat/impls/seq/seqvscat.c

VecScatterBegin_MPI_ToAll in src/vec/vscat/impls/vscat.c

VecScatterBegin_MPI_ToOne in src/vec/vscat/impls/vscat.c

Index of all Vec routines

Table of Contents for all manual pages

Index of all manual pages