class_docstr: Outputs object detection proposals by applying estimated bounding-box
  transformations to a set of regular boxes (called "anchors").
class_docstr_tok: ["Outputs","object","detection","proposals","by","applying","estimated","bounding-box","transformations","to","a","set","of","regular","boxes","(","called","``","anchors","''",")","."]
docstr: This layer does not propagate gradients.
docstr_tok: ["This","layer","does","not","propagate","gradients","."]
code: def backward(self, top, propagate_down, bottom):
      """This layer does not propagate gradients."""
      pass
  
file_path: CNTK/Examples/Image/Detection/utils/caffe_layers/proposal_layer.py
imports: import numpy
  import yaml
  from utils.caffe_layers.default_config import cfg
  from utils.rpn.generate_anchors import generate_anchors
  from utils.caffe_layers.bbox_transform import bbox_transform_inv, clip_boxes
  from utils.nms_wrapper import nms
label_desc: Use image node_id 4 for calling the ProposalLayer obj's underlying member method code with example usage: obj.backward(top, propagate_down, bottom) without return types