@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} }