class_docstr: encode the bounding boxes
class_docstr_tok: ["encode","the","bounding","boxes"]
code: def forward(self, edges):
      ctx = edges.src["pred_bbox"].context
      n = edges.src["pred_bbox"].shape[0]
      delta_src_obj = self.bbox_delta(
          edges.src["pred_bbox"], edges.dst["pred_bbox"]
      )
      delta_src_rel = self.bbox_delta(
          edges.src["pred_bbox"], edges.data["rel_bbox"]
      )
      delta_rel_obj = self.bbox_delta(
          edges.data["rel_bbox"], edges.dst["pred_bbox"]
      )
      result = nd.zeros((n, 12), ctx=ctx)
      result[:, 0:4] = delta_src_obj
      result[:, 4:8] = delta_src_rel
      result[:, 8:12] = delta_rel_obj
      return {"pred_bbox_additional": result}
  
imports: import pickle
  import dgl
  import gluoncv
  import mxnet
  import numpy
  from dgl.nn.mxnet import GraphConv
  from dgl.utils import toindex
  from mxnet import nd
  from mxnet.gluon import nn
label_desc: Use image node_id 3 for calling the EdgeBBoxExtend obj's underlying member method code with example usage: obj.forward(edges) and returns: dict