code: def _ref_sigmoid(x):
      if x >= 0:
          return 1 / (1 + np.exp(-x))
      else:
          z = np.exp(x)
          return z / (1 + z)
  
imports: import numpy
  from keras import activations
  from keras import backend
  from keras import testing
label_desc: Use image node_id 9 for calling a global function with example usage: _ref_sigmoid(x) and returns: unknown, unknown