code: def pairwise_iou(boxlist1, boxlist2):
      """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.
      """
      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),
      )
  
imports: import tensorflow
  from tensorpack.tfutils.scope_utils import under_name_scope
label_desc: Use image node_id 3 for calling a global function with example usage: pairwise_iou(boxlist1, boxlist2) and returns: tf