mp_sum_dm4 Subroutine

      SUBROUTINE mp_sum_dm4(msg, gid)
      !! Element-wise sum of a rank-4 array on all processes.
      !! @note see mp_sum_d

         REAL(kind=real_8), CONTIGUOUS, INTENT(INOUT)     :: msg(:, :, :, :)
         !! Array to sum and result
         INTEGER, INTENT(IN)                      :: gid

         CHARACTER(LEN=*), PARAMETER :: routineN = 'mp_sum_dm4'

         INTEGER                                  :: handle, ierr, &
                                                     msglen

         ierr = 0
         CALL timeset(routineN, handle)

         msglen = SIZE(msg)
#if defined(__parallel)
         IF (msglen > 0) THEN
            CALL mpi_allreduce(MPI_IN_PLACE, msg, msglen, MPI_DOUBLE_PRECISION, MPI_SUM, gid, ierr)
            IF (ierr /= 0) CALL mp_stop(ierr, "mpi_allreduce @ "//routineN)
         END IF
         CALL add_perf(perf_id=3, msg_size=msglen*real_8_size)
#else
         MARK_USED(gid)
#endif
         CALL timestop(handle)
      END SUBROUTINE mp_sum_dm4