VecGhostGetLocalForm — PETSc 3.23.0 documentation

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# VecGhostGetLocalForm

Obtains the local ghosted representation of a parallel vector (obtained with `VecCreateGhost()`, `VecCreateGhostWithArray()` or `VecCreateSeq()`).

## Synopsis

    #include "petscvec.h"
    PetscErrorCode VecGhostGetLocalForm(Vec g, Vec *l)

Logically Collective

## Input Parameter

- g - the global vector

## Output Parameter

- l - the local (ghosted) representation,`NULL` if `g` is not ghosted

## Notes

This routine does not actually update the ghost values, but rather it returns a sequential vector that includes the locations for the ghost values and their current values. The returned vector and the original vector passed in share the same array that contains the actual vector data.

To update the ghost values from the locations on the other processes one must call `VecGhostUpdateBegin()` and `VecGhostUpdateEnd()` before accessing the ghost values. Thus normal usage is

         VecGhostUpdateBegin(x,INSERT_VALUES,SCATTER_FORWARD);
         VecGhostUpdateEnd(x,INSERT_VALUES,SCATTER_FORWARD);
         VecGhostGetLocalForm(x,&xlocal);
         VecGetArray(xlocal,&xvalues);
            // access the non-ghost values in locations xvalues[0:n-1] and ghost values in locations xvalues[n:n+nghost];
         VecRestoreArray(xlocal,&xvalues);
         VecGhostRestoreLocalForm(x,&xlocal);

One should call `VecGhostRestoreLocalForm()` or `VecDestroy()` once one is finished using the object.

## See Also

Vectors and Parallel Data, `Vec`, `VecType`, `VecCreateGhost()`, `VecGhostRestoreLocalForm()`, `VecCreateGhostWithArray()`

## Level

advanced

## Location

src/vec/vec/impls/mpi/commonmpvec.c

## Examples

src/vec/vec/tutorials/ex14f.F90
src/vec/vec/tutorials/ex9.c
src/vec/vec/tutorials/ex9f.F90

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