code: def _grad_sigmoid(x):
      return x * (1 - x)
  
file_path: chainer/chainer/functions/rnn/tree_lstm.py
imports: import numpy
  import six
  import chainer
  from chainer import backend
  from chainer.backends import cuda
  from chainer import function
  from chainer.utils import type_check
  import chainerx
label_desc: Use image node_id 3 for calling a global function with example usage: _grad_sigmoid(x) and returns: unknown