@article{li2019nonsmooth,
  title={Nonsmooth optimization over stiefel manifold: Riemannian subgradient methods},
  author={Li, Xiao and Chen, Shixiang and Deng, Zengde and Qu, Qing and Zhu, Zhihui and So, Anthony Man Cho},
  journal={arXiv preprint arXiv:1911.05047},
  year={2019}
}