In plain words: They view gradient-following optimization as a system that evolves step by step, and use a stability theorem to show the unlucky starting points form a tiny set. So these methods almost never stall at a saddle point, without needing second derivatives or random noise.
Abstract · First-order Methods Almost Always Avoid Saddle Points
We establish that first-order methods avoid saddle points for almost all initializations. Our results apply to a wide variety of first-order methods, including gradient descent, block coordinate descent, mirror descent and variants thereof. The connecting thread is that such algorithms can be studied from a dynamical systems perspective in which appropriate instantiations of the Stable Manifold Theorem allow for a global stability analysis. Thus, neither access to second-order derivative information nor randomness beyond initialization is necessary to provably avoid saddle points.
Jason D. Lee, Ioannis Panageas, Georgios Piliouras, Max Simchowitz, Michael I. Jordan, Benjamin Recht
arXiv:1710.07406 · stat.ML, cs.LG, math.OC · submitted Oct 20, 2017
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