PyMC3中的隐马尔可夫模型问题

Question

为了学习PyMC，我尝试做一个简单的隐马尔可夫模型，如下所示：

with pymc3.Model() as hmm:
    # Transition "matrix"
    a_t = np.ones(num_states)
    T = [pymc3.Dirichlet('T{0}'.format(i), a = a_t,  shape = num_states) for i in xrange(num_states)]
    # Emission "matrix"
    a_e = np.ones(num_emissions)
    E = [pymc3.Dirichlet('E{0}'.format(i), a = a_e,  shape = num_emissions) for i in xrange(num_states)]
    # State models
    p0 = np.ones(num_states) / num_states
    # No shape, so each state is a scalar tensor
    states = [pymc3.Categorical('s0', p = p0)]
    emissions = [pymc3.Categorical('z0',
                               p = ifelse(eq(states[0], 0), E[0], ifelse(eq(states[0], 1), E[1], E[2])),
                               observed = example_observation[0])]
    for i in xrange(1, num_times):
        states.append(pymc3.Categorical('s{0}'.format(i),
                                    p = ifelse(eq(states[i-1], 0), T[0], ifelse(eq(states[i-1], 1), T[1], T[2]))))
        emissions.append(pymc3.Categorical('z{0}'.format(i),
                                    p = ifelse(eq(states[i], 0), E[0], ifelse(eq(states[i], 1), E[1], E[2])),
                                    observed = example_observation[i]))

我认为这个模型应该是正确的，但是当我尝试从这个模型中取样时，我得到了一个非常奇怪的InvalidValueError：

^{pr2}$

我已经上传了ipython notebook with the complete code。我做错什么了吗？在