student_t.py 文件源码

def _variance(self):
    var = (self._ones() *
           math_ops.square(self.sigma) * self.df / (self.df - 2))
    # When 1 < df <= 2, variance is infinite.
    inf = np.array(np.inf, dtype=self.dtype.as_numpy_dtype())
    result_where_defined = math_ops.select(
        math_ops.greater(self.df, array_ops.fill(self.batch_shape(), 2.)),
        var,
        array_ops.fill(self.batch_shape(), inf, name="inf"))

    if self.allow_nan_stats:
      nan = np.array(np.nan, dtype=self.dtype.as_numpy_dtype())
      return math_ops.select(
          math_ops.greater(self.df, self._ones()),
          result_where_defined,
          array_ops.fill(self.batch_shape(), nan, name="nan"))
    else:
      return control_flow_ops.with_dependencies([
          check_ops.assert_less(
              array_ops.ones((), dtype=self.dtype), self.df,
              message="variance not defined for components of df <= 1"),
      ], result_where_defined)