code: def forward(self, gy):
      if self._use_int_scale_forward:
          return self._integer_scale_forward(gy[0])
      if isinstance(gy[0], cuda.ndarray):
          gcol = conv.im2col_gpu(
              gy[0],
              self.kh,
              self.kw,
              self.sy,
              self.sx,
              self.ph,
              self.pw,
              cover_all=self.cover_all,
          )
      else:
          gcol = conv.im2col_cpu(
              gy[0],
              self.kh,
              self.kw,
              self.sy,
              self.sx,
              self.ph,
              self.pw,
              cover_all=self.cover_all,
          )
      gx = gcol.sum(axis=(2, 3))
      return (gx,)
  
imports: import numpy
  import numpy.lib.stride_tricks
  from chainer import backend
  from chainer.backends import cuda
  from chainer import function_node
  from chainer.functions.pooling import pooling_2d
  from chainer.utils import conv
  from chainer.utils import type_check
label_desc: Use image node_id 3 for calling the Unpooling2DGrad obj's underlying member method code with example usage: obj.forward(gy) and returns: gx, self