# VecScatterCreate#

Creates a vector scatter context.

## Synopsis#

#include "petscsf.h"
PetscErrorCode VecScatterCreate(Vec x, IS ix, Vec y, IS iy, VecScatter *newsf)


Collective

## Input Parameters#

• xin - a vector that defines the shape (parallel data layout of the vector) of vectors from which we scatter

• yin - a vector that defines the shape (parallel data layout of the vector) of vectors to which we scatter

• ix - the indices of xin to scatter (if NULL scatters all values)

• iy - the indices of yin to hold results (if NULL fills entire vector yin)

## Output Parameter#

• newsf - location to store the new scatter context

## Options Database Keys#

• -vecscatter_view - Prints detail of communications

• -vecscatter_view ::ascii_info - Print less details about communication

• -vecscatter_merge - VecScatterBegin() handles all of the communication, VecScatterEnd() is a nop eliminates the chance for overlap of computation and communication

## Notes#

If both xin and yin are parallel, their communicator must be on the same set of processes, but their process order can be different. In calls to the scatter options you can use different vectors than the xin and yin you used above; BUT they must have the same parallel data layout, for example, they could be obtained from VecDuplicate(). A VecScatter context CANNOT be used in two or more simultaneous scatters; that is you cannot call a second VecScatterBegin() with the same scatter context until the VecScatterEnd() has been called on the first VecScatterBegin(). In this case a separate VecScatter is needed for each concurrent scatter.

Both ix and iy cannot be NULL at the same time.

Use VecScatterCreateToAll() to create a vecscatter that copies an MPI vector to sequential vectors on all MPI ranks. Use VecScatterCreateToZero() to create a vecscatter that copies an MPI vector to a sequential vector on MPI rank 0. These special vecscatters have better performance than general ones.

Low-level Vector Communication, VecScatter, VecScatterDestroy(), VecScatterCreateToAll(), VecScatterCreateToZero(), PetscSFCreate()

intermediate

## Location#

src/vec/is/sf/interface/vscat.c

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