code: def _maxout(x, W, b):
      W_r = numpy.rollaxis(W, 2)
      y = numpy.tensordot(_as_mat(x), W_r, axes=1)
      if b is not None:
          y += b
      return numpy.max(y, axis=2)
  
imports: import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import gradient_check
  from chainer.initializers import constant
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
  from chainer.utils import type_check
label_desc: Use image node_id 2 for calling a global function with example usage: _maxout(x, W, b) and returns: numpy