code: def backward(self, indexes, grad_outputs):
      p, x, y = self.get_retained_inputs()
      (gz,) = grad_outputs
      return LinearInterpolateGrad().apply((p, x, y, gz))
  
file_path: chainer/chainer/functions/math/linear_interpolate.py
imports: from chainer.backends import cuda
  from chainer import function_node
  from chainer import utils
  from chainer.utils import type_check
label_desc: Use image node_id 4 for calling the LinearInterpolate obj's underlying member method code with example usage: obj.backward(indexes, grad_outputs) and returns: LinearInterpolateGrad