* QQ and ZZ contributed equally to the work. Invited review paper for
IEEE Signal Processing Magazine Special Issue on non-convex optimization for
signal processing and machine learning. This article contains 26 pages with
11 figures Access Paper or Ask Questions
* 6 pages, to appear at the 2019 Conference on Empirical Methods in
Natural Language Processing and 9th International Joint Conference on Natural
Language Processing (EMNLP-IJCNLP 2019) Access Paper or Ask Questions