def get_xaxis_bounds(plotnums):
    """ Get longest xaxis bounds for the plot
    so that all subplots have the same xaxis.
    """
    lower = upper = 0
    for x in plotnums:
        times = plotnums[x][0]
        l, u = times[0], times[-1]
        if l < lower:
            lower = l
        if u > upper:
            upper = u
    return lower, upper