text: from chainer import cuda
  from chainer import function_node
  from chainer import utils
  from chainer.utils import type_check
  
  
  class SquaredDifference(function_node.FunctionNode):
      """Squared difference of input variables."""
  
      def check_type_forward(self, in_types):
          type_check.expect(in_types.size() == 2)
          type_check.expect(
              in_types[0].dtype.kind == 'f',
              in_types[0].dtype == in_types[1].dtype,
              in_types[0].shape == in_types[1].shape
          )
  
      def forward(self, inputs):
          self.retain_inputs((0, 1))
          xp = cuda.get_array_module(*inputs)
          x1, x2 = inputs
          difference = x1 - x2
          y = xp.square(difference)
          return utils.force_array(y, dtype=x1.dtype),
  
      def backward(self, indexes, grads):
          gy, = grads
          x1, x2 = self.get_retained_inputs()
          difference = x1 - x2
          gx = gy * 2 * difference
          return gx, -gx
  
  
  def squared_difference(x1, x2):
      """Squared difference of input variables.
  
      Args:
          x1 (~chainer.Variable): Input variables to be compared.
          x2 (~chainer.Variable): Input variables to be compared.
  
      Returns:
          ~chainer.Variable: ``(x1 - x2) ** 2`` element-wise.
      """
      return SquaredDifference().apply((x1, x2))[0]
  