sum_allreduce_sub_real_3array Subroutine

  subroutine sum_allreduce_sub_real_3array (a,sub_comm)
    implicit none
    real, dimension (:,:,:), intent (in out) :: a
    integer, intent(in) :: sub_comm
# ifdef MPI
    integer :: ierror
!$OMP MASTER
    call time_message(.false., time_mp_collectives, ' MPI Collectives')
!$OMP END MASTER
    call mpi_allreduce &
         (MPI_IN_PLACE, a, size(a), mpireal, MPI_SUM, sub_comm, ierror)
!$OMP MASTER
    call time_message(.false., time_mp_collectives, ' MPI Collectives')
!$OMP END MASTER
# else
    UNUSED_DUMMY(sub_comm); UNUSED_DUMMY(a)
# endif
  end subroutine sum_allreduce_sub_real_3array