code: def sign(x):
      """Elementwise sign function.
  
      For a given input :math:`x`, this function returns :math:`sgn(x)`
      defined as
  
      .. math::
  
          sgn(x) = \\left \\{ \\begin{array}{cc}
          -1 & {\\rm if~x < 0} \\\\
          0 & {\\rm if~x = 0} \\\\
          1 & {\\rm if~x > 0} \\\\
          \\end{array} \\right.
  
      .. note::
  
          The gradient of this function is ``None`` everywhere and therefore
          unchains the computational graph.
  
      Args:
          x (:class:`~chainer.Variable` or :ref:`ndarray`):
              Input variable for which the sign is computed.
  
      Returns:
          ~chainer.Variable: Output variable.
  
      """
      if isinstance(x, chainer.variable.Variable):
          x = x.array
      xp = backend.get_array_module(x)
      return chainer.as_variable(utils.force_array(xp.sign(x)))
  
label_desc: Use image node_id 1 for calling a global function with example usage: sign(x) and returns: chainer