# 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.

PETSC_COMM_SELF

beginner

## Location#

include/petscsys.h

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