class_docstr: iou loss, see https://arxiv.org/abs/1908.03851
  loss = 1.0 - iou * iou
  Args:
      loss_weight (float): iou loss weight, default is 2.5
      max_height (int): max height of input to support random shape input
      max_width (int): max width of input to support random shape input
      ciou_term (bool): whether to add ciou_term
      loss_square (bool): whether to square the iou term
code: def __init__(
      self,
      loss_weight=2.5,
      giou=False,
      diou=False,
      ciou=False,
      loss_square=True,
  ):
      self.loss_weight = loss_weight
      self.giou = giou
      self.diou = diou
      self.ciou = ciou
      self.loss_square = loss_square
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import numpy
  import math
  import paddle
  from ppdet.core.workspace import register, serializable
  from ..bbox_utils import bbox_iou
label_desc: Use image node_id 1 to create a new IouLoss object from inherited base classes: object with example: obj = IouLoss(loss_weight, giou, diou, ciou, loss_square)