
CS Colloquium: Jason Lee (USC, Data Sciences and Operations)On the Foundations of Deep Learning: SGD, Overparametrization, and Generalization
Tue, Feb 19, 2019 @ 11:00 AM  12:00 PM
Thomas Lord Department of Computer Science
Conferences, Lectures, & Seminars
Speaker: Jason Lee, USC, Data Sciences and Operations
Talk Title: On the Foundations of Deep Learning: SGD, Overparametrization, and Generalization
Series: CS Colloquium
Abstract: We provide new results on the effectiveness of SGD and overparametrization in deep learning.
a) SGD: We show that SGD converges to stationary points for general nonsmooth , nonconvex functions, and that stochastic subgradients can be efficiently computed via Automatic Differentiation. For smooth functions, we show that gradient descent, coordinate descent, ADMM, and many other algorithms, avoid saddle points and converge to local minimizers. For a large family of problems including matrix completion and shallow ReLU networks, this guarantees that gradient descent converges to a global minimum.
b) Overparametrization: We show that gradient descent finds global minimizers of the training loss of overparametrized deep networks in polynomial time.
c) Generalization:
For general neural networks, we establish a marginbased theory. The minimizer of the crossentropy loss with weak regularization is a maxmargin predictor, and enjoys stronger generalization guarantees as the amount of overparametrization increases.
d) Algorithmic and Implicit Regularization: We analyze the implicit regularization effects of various optimization algorithms on overparametrized networks. In particular we prove that for least squares with mirror descent, the algorithm converges to the closest solution in terms of the bregman divergence. For linearly separable classification problems, we prove that the steepest descent with respect to a norm solves SVM with respect to the same norm. For overparametrized nonconvex problems such as matrix sensing or neural net with quadratic activation, we prove that gradient descent converges to the minimum nuclear norm solution, which allows for both meaningful optimization and generalization guarantees
This lecture satisfies requirements for CSCI 591: Research Colloquium
Biography: Jason Lee is an assistant professor in Data Sciences and Operations at the University of Southern California. Prior to that, he was a postdoctoral researcher at UC Berkeley working with Michael Jordan. Jason received his PhD at Stanford University advised by Trevor Hastie and Jonathan Taylor. His research interests are in statistics, machine learning, and optimization. Lately, he has worked on high dimensional statistical inference, analysis of nonconvex optimization algorithms, and theory for deep learning.
Host: Yan Liu
Location: Olin Hall of Engineering (OHE)  132
Audiences: Everyone Is Invited
Contact: Assistant to CS chair