code: def backward(self, dy):
      (arg,) = self.saved_tensors
      offsets = self.offsets
      m = offsets[-1].asscalar()
      if self.op == "sum":
          offsets_np = asnumpy(offsets[1:])
          indices_np = np.zeros((m + 1,), dtype=offsets_np.dtype)
          np.add.at(indices_np, offsets_np, np.ones_like(offsets_np))
          indices_np = np.cumsum(indices_np, -1)[:-1]
          indices = zerocopy_from_numpy(indices_np)
          dx = dy[indices]
      else:
          dx = _bwd_segment_cmp(dy, arg, m)
      return dx
  
imports: import mxnet
  import numpy
  from mxnet import nd
  from ..._sparse_ops import _bwd_segment_cmp, _csrmask, _csrmm, _csrsum, _gsddmm, _gspmm, _scatter_add, _segment_reduce
  from ...base import ALL, dgl_warning, is_all
  from ...heterograph_index import create_unitgraph_from_csr
  from .tensor import asnumpy, context, copy_to, to_backend_ctx, zerocopy_from_numpy
label_desc: Use image node_id 3 for calling the SegmentReduce obj's underlying member method code with example usage: obj.backward(dy) and returns: dx