Author: Aravind Reddy

Northwestern papers at FOCS 2020

The Northwestern CS Theory group had three papers at the 61st Annual IEEE Symposium on Foundations of Computer Science (FOCS 2020), which was recently held virtually.

Northwestern Economics PhD student Modibo Camara, CS PhD student Aleck Johnsen, and Prof. Jason Hartline co-authored a paper “Mechanisms for a No-Regret Agent: Beyond the Common Prior“.  The paper analyzes a broad class of Principal-Agent games in economics that normally depend on common knowledge of a precise distribution over an unknown, payoff-relevant input, using instead online learning in repeated game play.  A key idea of the paper which describes (possibly externally-informed) Agents behaviorally with only a no-regret property is to extend previous definitions for “regret” to consider counterfactual sequences of the repeated play. Link to the talk.

Northwestern CS PhD students Yingkai Li and Aleck Johnsen, and Prof. Jason Hartline co-authored a paper “Benchmark Design and Prior Independent Optimization“.  The paper introduces a formal approach to the study of benchmark design, as a parameter of worst case algorithm design to be optimized.  Incorporating first economic properties to justify and measure benchmarks, the main result of the paper shows that benchmark design is equivalent to algorithm design when inputs are drawn independently from a common-but-unknown distribution.  Another main result solves a longstanding open question in 2-agent revenue auction design, which further serves as application for the benchmark design result. Link to the talk.

Prof. Aravindan Vijayaraghavan co-authored a paper “Scheduling Precedence-Constrained Jobs on Related Machines with Communication Delay” with Biswaroop Maiti (Northeastern), Rajmohan Rajaraman (Northeastern), David Stalfa (Northeastern), and Zoya Svitkina (Google). The paper studies the problem of scheduling n precedence-constrained jobs on m uniformly-related machines in the challenging setting where we have to account for communication delays. Communication delay is the amount of time that must pass between the completion of a job on one machine and the start of any successor of that job on a different machine. The paper shows both algorithmic results and lower bounds. This includes the first polylogarithmic factor approximation algorithm for this problem, superconstant integrality gaps, and bounding the advantage of duplication in these settings. Link to the talk.

Seeking nominations for 2020 Junior Theorists Workshop

We are seeking nominations for outstanding final-year Ph.D. students or postdocs to present their recent research at the 2020 Junior Theorists Workshop on December 17 and 18. The workshop will visit broad themes in theoretical computer science and we expect to invite eight speakers. Due to the pandemic, the workshop will be virtual this year.

If you would like to nominate an outstanding student or postdoc from your institution, please submit the paper (URL or pdf) the speaker would likely present and a brief nomination statement here by Nov. 30. If you already have a letter of recommendation for the nominee that includes a discussion of the paper, that would be sufficient. Nomination letters will be kept in confidence. There is no need to check the availability and interest of the nominee before nominating.

We anticipate receiving more nominations than we can accept and will consider merit, breadth, diversity, and random coins in determining the program. In particular, we regret that the workshop will probably not be able to accommodate all outstanding nominees.

The Junior Theorists Workshop is part of our Quarterly Theory Workshop series and is in its third year. Details about last year’s Junior Theorists Workshop and other workshops in the Quarterly Theory Workshop series can be found on the events page.

New additions to Theory group

The Northwestern Theory group is excited to announce that we have several folks joining us at the beginning of this academic year! We have Hedyeh Beyhaghi as a postdoc joining from Cornell, Shravas Rao as a postdoc joining from NYU, Sumedha Uniyal as a visiting postdoc from Aalto University, Finland; Pattara Sukprasert as a new grad student transferring from the University of Maryland College Park; Saba Ahmadi and Sheng Yang, visiting grad students from the University of Maryland College Park.

Hedyeh Beyhaghi. Dr. Beyhaghi’s research interests are in Algorithm Design, with an emphasis on Algorithmic Game Theory and Mechanism Design. Her research mainly focuses on Auction Design, Online Stochastic Optimization, and Matching Markets. She obtained her Ph.D. at Cornell University, under the supervision of Eva Tardos.This text is only to create extra space for good indentation. Kudos to you if you found this text! Have a nice day. This text is only to create extra space for good indentation. Kudos to you if you found this text! Have a nice day.

 

Shravas Rao. Dr. Rao’s research interests are in theoretical computer science, with an emphasis on derandomization and pseudorandomness. He completed his Ph.D. at New York University advised by Oded Regev.This text is only to create extra space for good indentation. Kudos to you if you found this text! Have a nice day. This text is only to create extra space for good indentation. Kudos to you if you found this text!

 

Sumedha Uniyal. Dr. Uniyal is a postdoctoral researcher (Oct’17-Present) in the group of Prof. Parinya Chalermsook at Aalto University, Finland. She did her Ph.D. (Apr’13-Oct’17) at IDSIA, University of Lugano, Switzerland; under the supervision of Prof. Fabrizio Grandoni. She is broadly interested in approximation algorithms and algorithmic graph theory. During her Ph.D., she has worked on developing approximation algorithms for connectivity problems, clustering problems, and submodular optimization. Recently, she is also interested in structural graph theory and its implications in algorithms. She will be a visiting scholar at Northwestern till Dec’19 working with Prof. Samir Khuller.

 

Pattara Sukprasert. Pattara is a third-year Ph.D. student advised by Prof. Samir Khuller. He transferred from the University of Maryland College Park, where he spent his first two Ph.D. years and received a Master’s degree. Before that, he lived mostly in Thailand and got another Master’s degree from Kasetsart University advised by Prof. Jittat Fakcharoenphol. He is interested in approximation algorithms and graph theory, and has worked on network design problems, network flow problems, and some structural graph theory problems. Recently, he has also developed some interests in fast (up to sub-cubic) approximation algorithms.

 

Saba Ahmadi. Saba is a fifth year PhD student at the University of Maryland College Park visiting Northwestern, and she is advised by Prof. Samir Khuller. She is mainly interested in designing approximation algorithms. She is also interested in the topic of fairness and its relevance to combinatorial optimization. She finds problems at the intersection of AI and combinatorial optimization very interesting, one example is how to have diversity in the matching markets.

 

Sheng Yang. Sheng is a fifth year PhD student at University of Maryland, College Park advised by Prof. Samir Khuller. Currently, he is visiting Northwestern as a pre-doctoral visiting scholar. He is broadly interested in approximation algorithms. He has worked on graph theory topics related to connected dominating set and induced subgraph counting. Currently, he is mainly working on various scheduling problems, classical and new challenges originating from cloud computing.

Northwestern CS Theory group @ FCRC 2019

The Northwestern CS Theory group cumulatively had eight papers at conferences held as part of the ACM Federated Computing Research Conference(FCRC) 2019, which took place recently in Phoenix, AZ. We had two papers in COLT, four in EC, and one each in SPAA and STOC. Members of the group who attended include Professors Jason Hartline, Samir Khuller, Konstantin Makarychev, and Aravindan Vijayaraghavan, postdoc Xue Chen, PhD students Yiding Feng, Aleck Johnsen, Yingkai Li, and Aravind Reddy. Also in attendance were CS Prof. Jessica Hullman and Econ PhD student Modibo Camara.

Conference on Learning Theory(COLT):

TCS postdoc Xue Chen presented a joint paper “Active Regression via Linear-Sample Sparsification” with Eric Price (UT Austin). This paper gives an efficient algorithm with an optimal sample complexity for the classical problem of linear regression. Its techniques yield improved results for the non-linear sparse Fourier transform setting.

TCS Ph.D. student Yingkai Li presented a joint paper with Yining Wang (CMU) and Yuan Zhou (UIUC). The paper “Nearly Minimax-Optimal Regret for Linearly Parameterized Bandits” obtained almost tight dependence on the time horizon for regret minimization in linear bandits. One of the main results is to show that there is an extra sqrt(log T) factor in the lower bound, revealing a regret scaling quite different from classical multi-armed bandits. Our proof techniques include variable confidence levels and a careful analysis of layer sizes of SupLinUCB on the upper bound side, and delicately constructed adversarial sequences showing the tightness of elliptical potential lemmas on the lower bound side.

Economics and Computation(EC):

TCS Ph.D. alumnus Sam Taggart (Assist. Prof. Oberlin College) presented a joint paper with TCS Prof. Jason Hartline in the joint session of EC and STOC.  The paper, “Sample Complexity for Non-truthful Mechanisms“, describes a family of winner-pays-bid and all-pay (i.e., non-truthful) mechanisms that can be optimized from past bid data from the same market.  Most mechanisms in practice are non-truthful and, for example, the winner-pays-bid format is especially common.  The literature on sample complexity in mechanism design is well established, however, this paper is the first to consider non-truthful mechanisms.

TCS Prof. Jason Hartline presented a joint paper with TCS Ph.D. student Aleck Johnsen, Dennis Nekipelov (UVA), and Onno Zoeter (Booking.com).  The paper, “Dashboard Mechanisms for Online Marketplaces” gives a theoretical model for how a bidding dashboard can both make it easier for bidders in an online marketplace to optimize their bids and for the designer to optimize the mechanism.  A key idea in the paper is that if bidders optimize their bids for the dashboard, which predicts the outcome that will be obtained for any bid, then the underlying preferences of the bidders can be easily inferred from the bids.  Link to Video.

TCS Ph.D. student Yingkai Li presented a joint paper with TCS Prof. Jason Hartline and TCS Ph.D. student Yiding Feng.  The paper, “Optimal Auctions vs. Anonymous Pricing: Beyond Linear Utility“, introduces a approximation framework which approximately reduces the analysis of anonymous pricing for agents with non-linear utility to agents with linear utility in revenue-maximization. Applying this framework, constant approximation guarantee of anonymous pricing is shown for agents with public-budget utility, private-budget utility, and (a special case of) risk-averse utility.  A key idea in the paper is to define a parameterization of the regularity property that extends to agents with non-linear utility. Link to Video.

TCS Ph.D. student Chenhao Zhang had a joint paper with Nick Gravin (Shanghai University of Finance and Economics), Yaonan Jin (Columbia University) and Pinyan Lu (Shanghai University of Finance and Economics). The paper “Optimal Budget-Feasible Mechanisms for Additive Valuations” obtained tight approximation guarantee for budget-feasible mechanisms with an additive buyer. The paper proposes two-stage mechanisms that composite price-posting schemes with a pruning mechanism which greedily excludes the items with low value-per-cost ratios. A tight 2-approximation against the Knapsack and a tight 3-approximation against the Fractional-Knapsack are obtained by the proposed randomized and deterministic mechanisms respectively. Link to Video.

Symposium on Parallelism in Algorithms and Architectures(SPAA):

TCS Prof. Samir Khuller had a joint paper with visiting TCS PhD student Sheng Yang(UMD), Mosharaf Chowdhury(UMich), Manish Purohit(Google), and Jie You(UMich). The paper “Near Optimal Coflow Scheduling in Networks” focuses on the coflow scheduling problem which studies scheduling and data communication inter and intra datacenters. The main result is a randomized 2 approximation algorithm, significantly improving prior work both in theory and in practice.

Symposium on the Theory of Computing(STOC):

TCS Prof. Konstantin Makarychev had a paper with Yury Makarychev(TTIC) and Ilya Razenshteyn (Microsoft Research). This paper, “Performance of Johnson-Lindenstrauss Transform for k-Means and k-Medians Clustering“, shows that the cost of the optimal solution for Euclidean k-means or k-medians clustering is preserved up to a factor of (1+ε) under a projection onto a random O(log(k/ε)/ε2)-dimensional subspace. For k-means, this result resolves an open problem posed by Cohen, Elder, Musco, Musco, and Persu (STOC 2015); for k-medians, it answers a question raised by Kannan.