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SILO Seminar – Prakash Ishwar

Event Details

When: September 30, 2015, 12:30 PM

Location: 3rd Floor Orchard View Room , Discovery Building

Contact: 608-316-4401, hstampfli@wisc.edu

Prakash Ishwar

Prakash Ishwar, Assoc. Prof. ECE, Boston University

A Topic Modeling Approach to Learning Preference-Behavior from Pairwise Comparisons

The recent explosion of web analytics tools has enabled us to collect an immense amount of partial preferences for large sets of items such as products from Amazon, movies from Netflix, or restaurants from Yelp, from a large and diverse population of users through transactions, clicks, etc. Modeling, learning, and ultimately predicting the preference behavior of users from pairwise comparisons has been extensively studied since the 1927 work of Thurstone. Yet, almost all models to date have been founded on a clustering-perspective in which users are grouped by their preference behavior.

We take a fundamentally different decomposition-perspective and propose a new class of generative models for pairwise comparisons in which user preference behavior can be decomposed into contributions from multiple shared latent “causes” (partial orders) that are prevalent in the population. We show how the estimation of shared latent partial orders in the new generative model can be formally reduced to the estimation of topics in a statistically equivalent topic modeling problem in which causes correspond to topics and item-pairs to words. We show that an inevitable consequence of having a relatively small number of shared latent causes in a world of large number of item-pairs is the presence of “novel” item-pairs for each latent cause. We then leverage recent advances in the topic modeling literature and develop an algorithm based on extreme-point identification of convex polytopes to learn the shared latent partial orders. Our algorithm is provably consistent and comes with polynomial sample and computational complexity guarantees. We demonstrate that our new model is empirically competitive with the current state-of-the-art approaches in predicting preferences on semi-synthetic and real world datasets.

This talk is based on joint work with Weicong Ding and Venkatesh Saligrama at Boston University.

Prakash Ishwar received the BTech degree in EE from IIT Bombay in 1996 and the MS and PhD degrees in ECE from UIUC in 1998 and 2002 respectively.  After two years as a post-doctoral researcher in the EECS department at UC Berkeley, he joined the faculty of Boston University where he is currently Associate Professor of Electrical and Computer Engineering. His research interests are in information theory, information-theoretic security, statistical signal processing, machine learning, and visual information analysis and processing.

SILO is a lecture series with speakers from the UW faculty, graduate students or invited researchers that discuss mathematical related topics. The seminars are organized by WID’s Optimization research group.

SILO’s purpose is to provide a forum that helps connect and recruit mathematically-minded graduate students. SILO is a lunch-and-listen format, where speakers present interesting math topics while the audience eats lunch.