@article{imagecaptioningbasedonahierarchical,
  title = {Image Captioning Based on a Hierarchical Attention Mechanism and Policy Gradient Optimization},
  author = {Shi-Yang Yan and Yuan Xie and Fang-Yu Wu and Jeremy S. Smith and Wenjin Lu and Bai-Ling Zhang},
  year = {2018},
  eprint = {1811.05253},
  archivePrefix = {arXiv},
  url = {http://arxiv.org/abs/1811.05253v2},
}