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# PETSC_COMM_WORLD
the equivalent of the `MPI_COMM_WORLD` communicator which represents all the processes that PETSc knows about. 


## Notes
By default `PETSC_COMM_WORLD` and `MPI_COMM_WORLD` are identical unless you wish to
run PETSc on ONLY a subset of `MPI_COMM_WORLD`. In that case create your new (smaller)
communicator, call it, say comm, and set `PETSC_COMM_WORLD` = comm BEFORE calling
PetscInitialize(), but after `MPI_Init()` has been called.

The value of `PETSC_COMM_WORLD` should never be USED/accessed before `PetscInitialize()`
is called because it may not have a valid value yet.


## See Also
 `PETSC_COMM_SELF`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/include/petscsys.h.html#PETSC_COMM_WORLD">include/petscsys.h</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/dt/dualspace/impls/lagrange/tutorials/ex1.c.html">src/dm/dt/dualspace/impls/lagrange/tutorials/ex1.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/dt/dualspace/impls/lagrange/tutorials/ex2.c.html">src/dm/dt/dualspace/impls/lagrange/tutorials/ex2.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/field/tutorials/ex1.c.html">src/dm/field/tutorials/ex1.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/forest/tutorials/ex1.c.html">src/dm/impls/forest/tutorials/ex1.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/plex/tutorials/ex1.c.html">src/dm/impls/plex/tutorials/ex1.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/plex/tutorials/ex10.c.html">src/dm/impls/plex/tutorials/ex10.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/plex/tutorials/ex11.c.html">src/dm/impls/plex/tutorials/ex11.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/plex/tutorials/ex13.c.html">src/dm/impls/plex/tutorials/ex13.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/plex/tutorials/ex14.c.html">src/dm/impls/plex/tutorials/ex14.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/plex/tutorials/ex1f90.F90.html">src/dm/impls/plex/tutorials/ex1f90.F90</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/plex/tutorials/ex3f90.F90.html">src/dm/impls/plex/tutorials/ex3f90.F90</A><BR>


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