call MPI_INIT(ierr)
t0 = MPI_WTIME()

call MPI_ALLREDUCE(z0lc,z0gl,1,MPI_DOUBLE_PRECISION,&
                        MPI_SUM,MPI_COMM_WORLD,ierr)

t1 = MPI_WTIME()
time=t1-t0
call MPI_FINALIZE(ierr)