tf.contrib.distributions.Beta.log_cdf(value, name='log_cdf')
Log cumulative distribution function.
Given random variable X, the cumulative distribution function cdf is:
log_cdf(x) := Log[ P[X <= x] ]
Often, a numerical approximation can be used for log_cdf(x) that yields a more accurate answer than simply taking the logarithm of the cdf when x << -1.
Additional documentation from Beta:
Note that the argument x must be a non-negative floating point tensor whose shape can be broadcast