# High Dimensional Robust Principal Component Analysis

**Abstract:**

The analysis of very high dimensional data - data sets where the dimensionality of each observation is comparable to or even larger than the number of observations - has drawn increasing attention in the last few decades due to a broad array of applications, from DNA microarrays to video processing, to consumer preference modeling and collaborative filtering, and beyond. As we discuss, many of our tried-and-true statistical techniques fail in this regime.

We revisit one of the perhaps most widely used statistical techniques for dimensionality reduction: Principal Component Analysis (PCA). In the standard setting, PCA is computationally efficient, and statistically consistent, i.e., as the number of samples goes to infinity, we are guaranteed to recover the optimal low-dimensional subspace. On the other hand, PCA is well-known to be exceptionally brittle -- even a single corrupted point can lead to arbitrarily bad PCA output.

We consider PCA in the high-dimensional regime, where a constant fraction of the observations in the data set are arbitrarily corrupted. We show that many standard techniques fail in this setting, and discuss some of the unique challenges (and also opportunities) that the high-dimensional regime poses. For example, one of the (many) confounding features of the high-dimensional regime, is that the noise magnitude dwarfs the signal magnitude, i.e., SNR goes to zero. While in the classical regime, dimensionality recovery would fail under these conditions, sharp concentration-of-measure phenomena in high dimensions provide a way forward.

Then, for the main part of the talk, we propose a High-dimensional Robust Principal Component Analysis (HR-PCA) algorithm that is computationally tractable, robust to contaminated points, and easily kernelizable. The resulting subspace has a bounded deviation from the desired one, achieves maximal robustness, and unlike ordinary PCA algorithms, achieves optimality in the limit case where the proportion of corrupted points goes to zero.

**Biography:**

Constantine Caramanis obtained the A.B. degree in Mathematics from Harvard University, and the MS and PhD degrees from the Massachusetts Institute of Technology. Since 2006, he has been on the faculty in Electrical and Computer Engineering at The University of Texas at Austin. His research interests include robust and adaptable optimization and control, and statistics and machine learning, with applications to large scale networks.