code: def _sigmoid(x):
      half = x.dtype.type(0.5)
      return numpy.tanh(x * half) * half + half
  
file_path: chainer/tests/chainer_tests/functions_tests/activation_tests/test_swish.py
imports: import numpy
  from chainer import functions
  from chainer import testing
label_desc: Use image node_id 1 for calling a global function with example usage: _sigmoid(x) and returns: unknown