Title: First-order Methods Almost Always Avoid Saddle Points,
Abstract: 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.