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Previous Seminars

Learning by Random Features: Sharp Asymptotics and Universality Laws
Wed, Dec 8, 2021, 4:30 pm

Many new random matrix ensembles arise in learning and modern signal processing. As shown in recent studies, the spectral properties of these matrices help answer crucial questions regarding the training and generalization performance of neural networks, and the fundamental limits of high-dimensional signal recovery. As a result, there has been growing interest in precisely understanding the spectra and other asymptotic properties of these matrices. Unlike their classical counterparts, these new random matrices are often highly structured and are the result of nonlinear transformations. 

Bayesian Risk Optimization (BRO): A New Approach to Data-driven Stochastic Optimization
Wed, Dec 1, 2021, 4:30 pm

A large class of stochastic optimization problems involves optimizing an expectation taken with respect to an underlying distribution that is unknown in practice. One popular approach to addressing the distributional uncertainty, known as the distributionally robust optimization (DRO), is to hedge against the worst case among an ambiguity set of candidate distributions. However, given that worst-case rarely happens, inappropriate construction of the ambiguity set can sometimes result in over-conservative solutions. To explore the middle ground between optimistically ignoring the distributional uncertainty and pessimistically fixating on the worst-case scenario, we propose a Bayesian risk optimization (BRO) framework for parametric underlying distributions, which is to optimize a risk functional applied to the posterior distribution of the unknown distribution parameter. Of our particular interest are four risk functionals: mean, mean-variance, value-at-risk, and conditional value-at-risk. To reveal the implication of BRO, we establish the consistency of objective functions and optimal solutions, as well as the asymptotic normality of objective functions and optimal values. We also extend the BRO framework to online and multi-stage settings.

MCMC vs. Variational Inference -- for Credible Learning and Decision-Making at Scale
Tue, Nov 23, 2021, 4:30 pm

I will introduce some recent progress towards understanding the scalability of Markov chain Monte Carlo (MCMC) methods and their comparative advantage with respect to variational inference. I will discuss an optimization perspective on the infinite dimensional probability space, where MCMC leverages stochastic sample paths while variational inference projects the probabilities onto a finite dimensional parameter space. Three ingredients will be the focus of this discussion: non-convexity, acceleration, and stochasticity. This line of work is motivated by epidemic prediction, where we need uncertainty quantification for credible predictions and informed decision making with complex models and evolving data.

Optimal No-Regret Learning in Repeated First-Price Auctions
Wed, Nov 17, 2021, 4:30 pm

First-price auctions have very recently swept the online advertising industry, replacing second-price auctions as the predominant auction mechanism on many platforms for display ads bidding. This shift has brought forth important challenges for a bidder: how should one bid in a first-price auction, where unlike in second-price auctions, it is no longer optimal to bid one's private value truthfully and hard to know the others' bidding behaviors? In this paper, we take an online learning angle and address the fundamental problem of learning to bid in repeated first-price auctions. We discuss our recent work in leveraging the special structures of the first-price auctions to design minimax optimal no-regret bidding algorithms. 

CITP Seminar: Matt Weinberg – A Crash Course on Algorithmic Mechanism Design
Tue, Nov 16, 2021, 12:30 pm

Matt is an assistant professor at Princeton University in the Department of Computer Science. His primary research interest is in Algorithmic Mechanism Design: algorithm design in settings where users have their own incentives. He is also interested more broadly in Algorithmic Game Theory, Algorithms Under Uncertainty, and Theoretical Computer Science in general. Please click here for more details.

From Shallow to Deep Representation Learning: Global Nonconvex Theory and Algorithms
Fri, Nov 12, 2021, 4:30 pm

In this talk, we consider two fundamental problems in signal processing and machine learning: (convolutional) dictionary learning and deep network training. For both problems, we provide the first global nonconvex landscape analysis of the learned representations, which will in turn provide new guiding principles for better model/architecture design, optimization, robustness, and in both supervised and unsupervised scenarios. More specifically, the first part of the talk will focus on (convolutional) dictionary learning (aka shallow representation learning) in the unsupervised setting, we show that a nonconvex  L_4 loss over the sphere has no spurious local minimizers. This further inspires us to design efficient optimization methods for convolutional dictionary learning, with applications in imaging sciences. Second, we study the last-layer representation in deep learning, where recent seminal work by Donoho et al. showed a prevalence empirical phenomenon during the terminal phase of network training - neural collapse. By studying the optimization landscape of the training loss under an unconstrained feature model, we provide the theoretical justification for this phenomenon, which could have broad implications for network training, design, and beyond.

CITP Seminar: Alex Hanna – Beyond Bias: Algorithmic Unfairness, Infrastructure, and Genealogies of Data
Tue, Nov 9, 2021, 12:30 pm

Problems of algorithmic bias are often framed in terms of lack of representative data or formal fairness optimization constraints to be applied to automated decision-making systems. However, these discussions sidestep deeper issues with data used in AI, including problematic categorizations and the extractive logics of crowdwork and data mining. This talk will examine two interventions: first by reframing of data as a form of infrastructure, and as such, implicating politics and power in the construction of datasets; and secondly discussing the development of a research program around the genealogy of datasets used in machine learning and AI systems. These genealogies should be attentive to the constellation of organizations and stakeholders involved in their creation, the intent, values, and assumptions of their authors and curators, and the adoption of datasets by subsequent researchers.

Pranay Anchuri – Insights into Predictability of Life Outcomes: A Data-Driven Approach
Tue, Oct 26, 2021, 12:30 pm

Predicting life outcomes is a challenging task even for advanced machine learning (ML) algorithms. At the same time, accurately predicting these outcomes has important implications in providing targeted assistance and in improving policy making. Recent studies based on Fragile Families and Child Wellbeing Study dataset have shown that…

Bridging the Gap Between AI and Clinical Neuroscience via Deep-Generative Fusion Models
Thu, Oct 14, 2021, 4:30 pm

Deep learning has disrupted nearly every major field of study from computer vision to genomics. The unparalleled success of these models has, in many cases, been fueled by an explosion of data. Millions of labeled images, thousands of annotated ICU admissions, and hundreds of hours of transcribed speech are common standards in the literature. Clinical neuroscience is a notable holdout to this trend. It is a field of unavoidably small datasets, massive patient variability, and complex (largely unknown) phenomena. My lab tackles these challenges across a spectrum of projects, from answering foundational neuroscientific questions to translational applications of neuroimaging data to exploratory directions for probing neural circuitry. One of our key strategies in this data-starved regime has been to blend the structure and interpretability of classical methods with the representational power of deep learning.

Quantitative Social Science Colloquium: Measuring Housing Activeness from Multi-source Big Data and Machine Learning
Fri, Oct 8, 2021, 11:30 am

Measuring timely high-resolution socioeconomic outcomes is critical for policy-making and evaluation, but hard to reliably obtain. With the help of machine learning and cheaply available data such as social media and nightlight, it is now possible to predict such indices in fine granularity. This paper demonstrates an adaptive way to measure the time trend and spatial distribution of housing activeness with the help of multiple easily-accessible datasets.