class_docstr: Chi-Square Distribution.
  
  The probability density function of the distribution is expressed as
  
  .. math::
      p(x;k) = \frac{1}{2^{k/2}\Gamma(k/2)}x^{k/2-1}e^{-x/2}
  
  Args:
      k(:class:`~chainer.Variable` or :ref:`ndarray`): Parameter of
          distribution.
code: def _half_k(self):
      return 0.5 * self.k
  
imports: import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import distribution
  from chainer.functions.math import digamma
  from chainer.functions.math import exponential
  from chainer.functions.math import lgamma
  from chainer.utils import cache
label_desc: Use image node_id 3 for calling the Chisquare obj's underlying member method code with example usage: obj._half_k() and returns: unknown