code: def box_xyxy_to_cxcywh(x):
      x0, y0, x1, y1 = x.unbind(-1)
      b = [(x0 + x1) / 2, (y0 + y1) / 2, (x1 - x0), (y1 - y0)]
      return paddle.stack(b, axis=-1)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from ppdet.core.workspace import register, create, merge_config
  import paddle
  import numpy
  import paddle
  import paddle.nn.functional
  from ppdet.core.workspace import register, create
  from ppdet.utils.logger import setup_logger
  from ppdet.modeling.ssod.utils import filter_invalid
  from .multi_stream_detector import MultiSteamDetector
label_desc: Use image node_id 2 for calling a global function with example usage: box_xyxy_to_cxcywh(x) and returns: paddle