environment/share/doc/ipython/examples/parallel/wave2D/parallelwave-mpi.py
def wave_saver(u, x, y, t):
    """save the wave log"""
    global u_hist
    global t_hist
    t_hist.append(t)
    u_hist.append(1.0*u)
def wave_saver(u, x, y, t):
    """save the wave log"""
    global u_hist
    global t_hist
    t_hist.append(t)
    u_hist.append(1.0*u)
save the wave log