在 PYMC3 中使用自定义似然会导致“预期 ndarray"错误

在 PYMC3 中使用自定义似然会导致“预期 ndarray

问题描述：

我正在尝试在 PYMC3 中使用自定义分布(广义极值或 GEV 分布).我已经写了一些代码来计算这个，但是我得到了一个

I'm trying to use a custom distribution (Generalized Extreme Value or GEV distribution) in PYMC3. I have written some code to compute this, but I get an error of

ValueError: 需要一个 ndarray应用导致错误的节点:MakeVector{dtype='float64'}(logp_sigma_log, __logp_mu, __logp_xi, __logp_x)

ValueError: expected an ndarray Apply node that caused the error: MakeVector{dtype='float64'}(logp_sigma_log, __logp_mu, __logp_xi, __logp_x)

代码如下:

@theano.as_op(itypes=[tt.dvector, tt.dscalar, tt.dscalar, tt.dscalar],
              otypes=[tt.dscalar])
def likelihood_op(values, mu, sigma, xi):
    logp = 0.
    for val in values:
        logp += genextreme.logpdf(val,-xi,loc=mu,scale=sigma)
    return logp

def gev_ll(values):
    return likelihood_op(values, mu, sigma, xi)



with pymc3.Model() as model:
    mean_sigma = 0.0
    sd_sigma   = 5.0
    sigma      = pymc3.Lognormal('sigma',mu = mean_sigma,tau = sd_sigma)

    mean_mu = 0.0
    sd_mu   = 40.0
    mu      = pymc3.Normal('mu',mu=mean_mu,sd =sd_mu)

    mean_xi = 0.0
    sd_xi   = 2.0
    xi      = pymc3.Normal('xi',mu = mean_xi, sd = sd_xi)

    x = pymc3.DensityDist('x',gev_ll,observed = np.squeeze(maxima.values ))
    step = pymc3.Metropolis()
    trace = pymc3.sample(draws=1000,step=step,n_int = 10000,tune = 1000,n_jobs = 4)
    print 'Gelman-Rubin diagnostic: {0}'.format(pymc3.diagnostics.gelman_rubin(trace))

答

原来这个错误是因为 likelihood_op 的返回值需要是一个 numpy 数组.一旦我改变了

It turns out that this error was because the return value of likelihood_op needed to be a numpy array. Once I changed

def likelihood_op(values, mu, sigma, xi):
    logp = 0.
    for val in values:
        logp += genextreme.logpdf(val,-xi,loc=mu,scale=sigma)
    return logp

到

def likelihood_op(values, mu, sigma, xi):
    logp = 0.
    for val in values:
        logp += genextreme.logpdf(val,-xi,loc=mu,scale=sigma)
    return np.array(logp)

然后图形编译得很好，我就可以采样了.

then the graph was compiled fine and I was able to sample.

在 PYMC3 中使用自定义似然会导致“预期 ndarray"错误

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