class_docstr: Gumbel Distribution.
  
  The probability density function of the distribution is expressed as
  
  .. math::
     f(x) = \frac{1}{\eta}            \exp\left\{ - \frac{x - \mu}{\eta} \right\}            \exp\left[-\exp\left\{-\frac{x - \mu}{\eta}            \right\}\right],
  
  Args:
      loc(:class:`~chainer.Variable` or :ref:`ndarray`): Parameter of
          distribution :math:`\mu`.
      scale(:class:`~chainer.Variable` or :ref:`ndarray`): Parameter of
          distribution :math:`\eta`.
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code: def __init__(self, loc, scale):
      super(Gumbel, self).__init__()
      self.__loc = loc
      self.__scale = scale
  
imports: import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import distribution
  from chainer.functions.math import exponential
  from chainer.functions.math import lgamma
  from chainer.utils import cache
label_desc: Use image node_id 1 to create a new Gumbel object from inherited base classes: distribution with example: obj = Gumbel(loc, scale)