code: def pairwise_iou(boxlist1, boxlist2):
      
      intersections = pairwise_intersection(boxlist1, boxlist2)
      areas1 = area(boxlist1)
      areas2 = area(boxlist2)
      unions = (
          tf.expand_dims(areas1, 1) + tf.expand_dims(areas2, 0) - intersections)
      return tf.where(
          tf.equal(intersections, 0.0),
          tf.zeros_like(intersections), tf.truediv(intersections, unions))
docs: Computes pairwise intersection-over-union between box collections.
  
      Args:
        boxlist1: Nx4 floatbox
        boxlist2: Mx4
  
      Returns:
        a tensor with shape [N, M] representing pairwise iou scores.