code: def bbox_improve(bbox):
      """bbox encoding"""
      area = (bbox[:, 2] - bbox[:, 0]) * (bbox[:, 3] - bbox[:, 1])
      return nd.concat(bbox, area.expand_dims(1))
  
file_path: dgl/examples/mxnet/scenegraph/utils/build_graph.py
imports: import dgl
  import numpy
  from mxnet import nd
label_desc: Use image node_id 1 for calling a global function with example usage: bbox_improve(bbox) and returns: nd