code: def sigmoid(x):
      return numpy.tanh(x * 0.5) * 0.5 + 0.5
  
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  import chainer.functions
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import backend
  from chainer.testing import condition
label_desc: Use image node_id 2 for calling a global function with example usage: sigmoid(x) and returns: unknown