code: def sigmoid(x):
      return 1 / (1 + numpy.exp(-x))
  
imports: import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 1 for calling a global function with example usage: sigmoid(x) and returns: unknown