def zoom(ax, xy='x', factor=1):
    """Zoom into axis.

    Parameters
    ----------
    """
    limits = ax.get_xlim() if xy == 'x' else ax.get_ylim()
    new_limits = (0.5*(limits[0] + limits[1])
                  + 1./factor * np.array((-0.5, 0.5)) * (limits[1] - limits[0]))
    if xy == 'x':
        ax.set_xlim(new_limits)
    else:
        ax.set_ylim(new_limits)
Zoom into axis.

    Parameters
    ----------