from tensorflow.python.ops import math_ops

      ```

      where digamma(alpha) is the digamma function.""")
  def _entropy(self):
    return (self.alpha +
            math_ops.log(self.beta) +
            math_ops.lgamma(self.alpha) -
            (1. + self.alpha) * math_ops.digamma(self.alpha))

  @distribution_util.AppendDocstring(
