我正在尝试在 PyMC3 上运行一个简单的逻辑回归。这里的代码：

with pm.Model() as logistic_model:
    alpha=pm.Normal('alpha', mu=0, sd=100)
    beta1=pm.Normal('beta', mu=0, sd=100)
    beta2=pm.Normal('beta2', mu=0, sd=100)

    argtemp=alpha + beta1*data['age'].values +beta2*data['educ'].values
    prob=pm.invlogit(argtemp)
    Y_obs = pm.Bernoulli('Y_obs', p=prob, observed=data['income_more_50K'].values)
    map_estimate = pm.find_MAP()
    sampler=pm.Metropolis()

    trace= pm.sample(40000, step=sampler, start=map_estimate)

采样器运行，但最后它给出了这个错误：

The gelman-rubin statistic is larger than 1.4 for some parameters. The sampler did not converge.
The estimated number of effective samples is smaller than 200 for some parameters.

有人可以帮助我理解什么是错的，为什么采样器不收敛？

谢谢！