def _metzner_figure_4():
    """Generate figure 4 from Metzner's paper [1].
    
    This can be used as a rough test of the sampler
    """
    import matplotlib.pyplot as pp
    def _scatter(Ts, xi, xj, yi, yj):
        pp.grid(False)
        pp.hexbin(Ts[:, xi, xj], Ts[:, yi, yj], cmap='hot_r', vmin=0, vmax=100)
        pp.xlabel('T_{%d,%d}' % (xi+1, xj+1))
        pp.ylabel('T_{%d,%d}' % (yi+1, yj+1))
        pp.plot([0,1], [1,0], c='k')
        pp.ylim(0, 1)
        pp.xlim(0, 1)
    
    C = np.array([[1, 10, 2], [2, 26, 3], [15, 20, 20]])
    Ts = np.array(list(metzner_mcmc_slow(C, 100000)))

    pp.figure(figsize=(6, 6)); pp.subplot(axisbg=(0,0,0,0))
    _scatter(Ts, 0, 1, 0, 2)

    pp.figure(figsize=(6, 6)); pp.subplot(axisbg=(0,0,0,0))
    _scatter(Ts, 1, 0, 1, 2)
    pp.figure(figsize=(6, 6)); pp.subplot(axisbg=(0,0,0,0))
    _scatter(Ts, 2, 0, 2, 1)
    pp.show()
Generate figure 4 from Metzner's paper [1].
    
    This can be used as a rough test of the sampler