VecGhostUpdateBegin#

Begins the vector scatter to update the vector from local representation to global or global representation to local.

Synopsis#

#include "petscvec.h"   
PetscErrorCode VecGhostUpdateBegin(Vec g, InsertMode insertmode, ScatterMode scattermode)

Neighbor-wise Collective

Input Parameters#

g - the vector (obtained with VecCreateGhost() or VecDuplicate())
insertmode - one of ADD_VALUES, MAX_VALUES, MIN_VALUES or INSERT_VALUES
scattermode - one of SCATTER_FORWARD or SCATTER_REVERSE

Notes#

Use the following to update the ghost regions with correct values from the owning process

       VecGhostUpdateBegin(v,INSERT_VALUES,SCATTER_FORWARD);
       VecGhostUpdateEnd(v,INSERT_VALUES,SCATTER_FORWARD);

Use the following to accumulate the ghost region values onto the owning processors

       VecGhostUpdateBegin(v,ADD_VALUES,SCATTER_REVERSE);
       VecGhostUpdateEnd(v,ADD_VALUES,SCATTER_REVERSE);

To accumulate the ghost region values onto the owning processors and then update the ghost regions correctly, call the latter followed by the former, i.e.,

       VecGhostUpdateBegin(v,ADD_VALUES,SCATTER_REVERSE);
       VecGhostUpdateEnd(v,ADD_VALUES,SCATTER_REVERSE);
       VecGhostUpdateBegin(v,INSERT_VALUES,SCATTER_FORWARD);
       VecGhostUpdateEnd(v,INSERT_VALUES,SCATTER_FORWARD);