Poster
Stochastic PCA with $\ell_2$ and $\ell_1$ Regularization
Poorya Mianjy · Raman Arora

Wed Jul 11th 06:15 -- 09:00 PM @ Hall B #17

We revisit convex relaxation based methods for stochastic optimization of principal component analysis (PCA). While methods that directly solve the nonconvex problem have been shown to be optimal in terms of statistical and computational efficiency, the methods based on convex relaxation have been shown to enjoy comparable, or even superior, empirical performance -- this motivates the need for a deeper formal understanding of the latter. Therefore, in this paper, we study variants of stochastic gradient descent for a convex relaxation of PCA with (a) $\ell2$, (b) $\ell1$, and (c) elastic net ($\ell1+\ell2)$ regularization in the hope that these variants yield (a) better iteration complexity, (b) better control on the rank of the intermediate iterates, and (c) both, respectively. We show, theoretically and empirically, that compared to previous work on convex relaxation based methods, the proposed variants yield faster convergence and improve overall runtime to achieve a certain user-specified $\epsilon$-suboptimality on the PCA objective. Furthermore, the proposed methods are shown to converge both in terms of the PCA objective as well as the distance between subspaces. However, there still remains a gap in computational requirements for the proposed methods when compared with existing nonconvex approaches.

Author Information

Poorya Mianjy (Johns Hopkins University)
Raman Arora (Johns Hopkins University)

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