April 2019 - talks - lists.cs.princeton.edu

Reminder: Angela Zhou, TODAY at 12:30, Friend 112
by Emily Lawrence 30 Apr '19

30 Apr '19

Informal Research Talk Angela Zhou from Cornell Tuesday, April 30 - 12:30 pm Friend Center - Room 112 Host: Barbara Engelhardt Safely Learning to Personalize from Observational Data Some of the most impactful applications of machine learning are not just about prediction but are rather about taking the right action, directed at the right target, at the right time. The goal of our work is to extract causal-effect-maximizing personalized decision rules from observational data in sensitive applications. Observational data, the norm rather than the exception in domains such as medicine and civics, lack experimental manipulation so that isolated causal effects are obscured by complex selection processes, a phenomenon known as confounding. We develop a framework for learning personalized decision policies from observational data while accounting for possible unobserved confounding in the data-generating process. In contrast, the previous literature assumes that all confounders are observed, an unverified assumption that is generally violated in practice. Under the Neyman-Rubin potential outcomes framework, policy evaluation is analogous to assessing subgroup treatment effects: policy learning parametrizes the subgroup by a machine learning predictor of who should be treated. We calibrate policy learning for realistic violations of this unverifiable assumption with uncertainty sets for inverse propensity weights motivated by sensitivity analysis in causal inference. Our framework for confounding-robust policy improvement optimizes the minimax regret of a candidate policy against a baseline standard-of-care policy over an uncertainty set. We prove that if the uncertainty set is well-specified, our robust policy, when applied in practice, will do no worse than the baseline and improve upon it if possible, and that it is asymptotically minimax optimal. We use efficient algorithmic solutions to optimize over parametrized spaces of decision policies such as logistic treatment assignment and decision trees. We assess our methods on synthetic data and on a large clinical trial, demonstrating that hidden confounding can hinder existing policy learning approaches, while our robust approach guarantees safety and focuses on well-evidenced improvement, a necessity for making personalized treatment policies learned from observational data reliable in practice. A conference version of this work appeared at Neurips 2018 and an extended version is under Major Revision at Management Science. Bio: Angela Zhou is a third-year PhD student at Cornell in Operations Research and Information Engineering. She is currently located at Cornell Tech (NYC) where she is very fortunate to be advised by Nathan Kallus. Her work is supported on a NDSEG fellowship. Previously, she studied Operations Research and Financial Engineering at Princeton University. -- Jonathan Lu | Princeton University | Class of 2019 Department of Computer Science, Master's Program jhlu(a)princeton.edu | (510) 779-4158

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Tomorrow: Angela Zhou Tuesday April 30 12:30-1:30 PM Friend 112
by Emily Lawrence 29 Apr '19

29 Apr '19

Angela Zhou (ORFE '15), currently a third-year PhD student at Cornell in Operations Research and Information Engineering working with Nathan Kallus, will be speaking about her machine learning and causal inference work: "Safely Learning to Personalize from Observational Data". She does thoughtful and fascinating work. Y'all should come out-- there will be lunch (vegan options available)! Informal Research Talk Angela Zhou from Cornell Tuesday, April 30 - 12:30 pm Friend Center - Room 112 Host: Barbara Engelhardt Safely Learning to Personalize from Observational Data Some of the most impactful applications of machine learning are not just about prediction but are rather about taking the right action, directed at the right target, at the right time. The goal of our work is to extract causal-effect-maximizing personalized decision rules from observational data in sensitive applications. Observational data, the norm rather than the exception in domains such as medicine and civics, lack experimental manipulation so that isolated causal effects are obscured by complex selection processes, a phenomenon known as confounding. We develop a framework for learning personalized decision policies from observational data while accounting for possible unobserved confounding in the data-generating process. In contrast, the previous literature assumes that all confounders are observed, an unverified assumption that is generally violated in practice. Under the Neyman-Rubin potential outcomes framework, policy evaluation is analogous to assessing subgroup treatment effects: policy learning parametrizes the subgroup by a machine learning predictor of who should be treated. We calibrate policy learning for realistic violations of this unverifiable assumption with uncertainty sets for inverse propensity weights motivated by sensitivity analysis in causal inference. Our framework for confounding-robust policy improvement optimizes the minimax regret of a candidate policy against a baseline standard-of-care policy over an uncertainty set. We prove that if the uncertainty set is well-specified, our robust policy, when applied in practice, will do no worse than the baseline and improve upon it if possible, and that it is asymptotically minimax optimal. We use efficient algorithmic solutions to optimize over parametrized spaces of decision policies such as logistic treatment assignment and decision trees. We assess our methods on synthetic data and on a large clinical trial, demonstrating that hidden confounding can hinder existing policy learning approaches, while our robust approach guarantees safety and focuses on well-evidenced improvement, a necessity for making personalized treatment policies learned from observational data reliable in practice. A conference version of this work appeared at Neurips 2018 and an extended version is under Major Revision at Management Science. Bio: Angela Zhou is a third-year PhD student at Cornell in Operations Research and Information Engineering. She is currently located at Cornell Tech (NYC) where she is very fortunate to be advised by Nathan Kallus. Her work is supported on a NDSEG fellowship. Previously, she studied Operations Research and Financial Engineering at Princeton University. -- Jonathan Lu | Princeton University | Class of 2019 Department of Computer Science, Master's Program jhlu(a)princeton.edu <mailto:jhlu@princeton.edu> | (510) 779-4158

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Jake Silverman will present his General Exam on May 7, 2019 at 2pm in CS 302
by Nicki Mahler 29 Apr '19

29 Apr '19

Jake Silverman will present his General Exam on May 7, 2019 at 2pm in CS 302. The members of his committee are as follows: Zak Kincaid (adviser), Aarti Gupta, and Andrew Appel. Everyone is invited to attend his talk, and those faculty wishing to remain for the oral exam following are welcome to do so. His abstract and reading list follow below. Title: Loop Summarization with Rational Vector Addition Systems Abstract: Modern software verification techniques employ a number of heuristics for reasoning about loops. While these heuristics are often effective, they are unpredictable. For example, abstract interpretation analyses sometimes have an unobtainable least fixed and rely on widening and narrowing operations. In this talk, I present a predictable abstract-interpretation based technique for computing numerical loop summaries. The technique works by first synthesizing a rational vector addition system with resets (Q-VASR) that simulates the action of an input loop, and then uses the (polytime computable) reachability relation of Q-VASRs to over-approximate the behavior of the loop. The key contribution presented (and the crux behind the predictability claim) is the ability to synthesize a Q-VASR that is a best abstraction of a LRA loop in the sense that (1) it simulates the loop and (2) it is simulated by any other Q-VASR that simulates the loop. In addition, I present a technique for improving the precision of the analysis by using Q-VASR with states to capture loop control structure. These techniques have been benchmarked against state-of-the-art tools; experiments show that these techniques are both precise and performant. The reading list papers are C. Calcagno, D. Distefano, P. W. O’Hearn, and H. Yang. Compositional shape analysis by means of bi-abduction, in: Proc. Symposium on Principles of Programming Languages (POPL ’09), pages 289–300. ACM Press, 2009. M. Colon, S. Sankaranarayanan, and H. Sipma, Linear invariant generation using non-linear constraint solving, in: International Conference on Computer-Aided Verification (CAV ‘03), pages 420–432 P. Cousot and R. Cousot, Abstract interpretation: a unified lattice model for static analysis of programs by construction or approximation of fixpoints, in: Proc. Symposium on Principles of Programming Languages (POPL ‘77). ACM Press, New York, 1977. A. Farzan and Z. Kincaid. Compositional Recurrence Analysis. In: Proc Formal Methods in Computer-Aided Design (FMCAD ’15). C. Haase and S. Halfon. Integer vector addition systems with states. in Proc: International Workshop on Reachability Problems (RP ‘14), volume 8762 of Lecture Notes in Computer Science, pages 112–124. Springer, 2014 F. Konecny. PTIME computation of transitive closures of octagonal relations. in Proc: International Conference on Tools and Algorithms for the Construction and Analysis of Systems (TACAS 2016). K. L. McMillan. Lazy abstraction with interpolants. in: Proc International Conference on Computer-Aided Verification (CAV ‘06), pages 123–136. Springer-Verlag, Berlin, Germany, M. Müller-Olm and H. Seidl. Precise interprocedural analysis through linear algebra. in Proc: Symposium on Principles of Programming Languages (POPL ’04). T. Reps, S. Horwitz and M. Sagiv, Precise interprocedural dataflow analysis via graph reachability, in Proc: ACM Symposium on Principles of Programming Languages (POPL ‘95), pages 49-61. T. Reps, M. Sagiv, and G. Yorsh. Symbolic implementation of the best transformer. in Proc. International Conference on Verification, Model Checking, and Abstract Interpretation (VMCAI ‘04). R. E. Tarjan, A unified approach to path problems, J. ACM, 28(3), 577–593 (1981). The reading list books are A.R. Bradley, Z. Manna. The Calculus of Computation: Decision Procedures with Applications to Verification. Springer, Heidelberg (2007) F. Nielson, H. Riis Nielson, and C. Hankin, Principles of Program Analysis, Springer-Verlag, 1999.

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Michael Uhlar and Sathya Gunasekar from Facebook, Friday, May 3
by Emily C. Lawrence 29 Apr '19

29 Apr '19

Michael Uhlar and Sathya Gunasekar from Facebook Friday, May 3 at 12:30pm Computer Science - Room 104 (large auditorium) [ https://www.cs.princeton.edu/events/25851 | https://www.cs.princeton.edu/events/25851 ] CacheLib - Unifying & Abstracting HW for caching @ Facebook In order to operate with high efficiency, Facebook’s infrastructure relies on caching in many different backend services. These services place very different demands on their caches, e.g., in terms of working set sizes, access patterns, and throughput requirements. Historically, each service used a different cache implementation, leading to inefficiency, duplicated code and effort. CacheLib is an embedded caching engine, which addresses this requirement with a unified API for building a cache implementation across many HW mediums. CacheLib transparently combines volatile and non-volatile storage in a single caching abstraction. To meet the varied demands, CacheLib successfully provides a flexible, high-performance solution for many different services at Facebook. In this talk, we describe CacheLib’s design, challenges, and several lessons learned.

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Bill Buxton Seminar, Monday April 29, 4:30pm. Friend Convocation Room
by Margaret Martonosi 26 Apr '19

26 Apr '19

Hello all- Dr. Bill Buxton, Principal Researcher at Microsoft, will be on campus Monday April 29. He’s giving a seminar at 4:30pm in the Friend Convocation room and we really hope lots of you will be there. Please forward to students as well, particularly those interested in Graphics, HCI, and Design. thanks, mrm > Buxton-Microsoft Collection On the Importance of History Shaping the Future > Monday, April 29th 4:30pm > Friend Center, Convocation Room > Speaker: Bill Buxton, Principal Researcher at Microsoft Research > Free and open to the public. Registration required. > > https://www.tfaforms.com/4734441 > > History, backed up by current data, tells us that what we perceive as rapid technological change is generally due to a large number of technologies evolving slowly. > > Over the past 45 years I have accumulated a collection of gadgets that captures the history of technological growth. For you, the value may just be nostalgia. However, my hope is this. In this age where the things which we produce create such a strong cultural impact, can we really afford not to take advantage of the learnings of the past hidden in plain sight? > > BIO > A Principal Researcher at Microsoft Research, Bill has had a 40- year involvement in research, practice and commentary around design, innovation and human aspects of technology. Following a 20-year career as a professional musician, he morphed into a researcher and interaction designer, at the University of Toronto, Xerox PARC, Alias Research and SGI Inc. He has been awarded four honourary doctorates, is co-recipient of an Academy Award for Scientific and Technical Achievement, received an ACM/SIGCHI Lifetime Achievement Award, and is a Fellow of the ACM. Bill has published, lectured and consulted widely, and is an Adjunct Professor at the University of Toronto, and a Distinguished Professor of Industrial Design at the Technical University Eindhoven. Other than his family, mountains and rivers are his first love. For more information, see billbuxton.com Margaret Martonosi H. T. Adams '35 Professor of Computer Science. Director, Keller Center for Innovation in Engineering Education Princeton University ■ mrm(a)princeton.edu ■ http://www.princeton.edu/~mrm

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Nora Willett will present her FPO "Tools for Live 2D Animation" on Tuesday, 5/7/2019 at 2pm in CS 402
by Nicki Mahler 24 Apr '19

24 Apr '19

Nora Willett will present her FPO "Tools for Live 2D Animation" on Tuesday, 5/7/2019 at 2pm in CS 402. The members of her committee are as follows: Adam Finkelstein (adviser), Readers: Thomas Funkhouser and Wilmot Li (Adobe Research); Examiners: Szymon Rusinkiewicz, Marshini Chetty, and Adam Finkelstein. A copy of her thesis is available upon request. Everyone is invited to attend her talk. The talk abstract follows below: Live animation of 2D characters is an emerging form of storytelling that has begun to appear on streaming platforms and broadcast TV. Unlike traditional animation, human performers control characters in real time so that they can respond and improvise to live events. Current live animation systems provide a range of animation controls, such as camera input to drive head movements, audio for lip sync, and keyboard shortcuts to trigger discrete pose changes via artwork swaps. However, managing all of these controls during a live performance is challenging. This dissertation presents four tools to assist performers in creating compelling live 2D animation. To create more compelling characters, we propose three tools to control artwork layers’ swaps and deformations. First, we introduce an interactive system that addresses the problem of triggering artwork swaps in live settings. Next, another system transfers poses from an input video to a character, automatically driving new animation through pose data. We also describe a framework that augments the primary motion of a character by adding secondary motion - subtle movement of parts like hair, foliage or cloth that complements and emphasizes the primary motion. To add more details to scene backgrounds, we show a mixed initiative interface which, from a few user-drawn scribbles, extracts repetitive texture elements in an image, and supports animating them.

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Seyed Sobhan Mir Yoosefi will present his General Exam on Thursday, May 2nd, 2019 at 10:45am in CS 401
by Nicki Mahler 24 Apr '19

24 Apr '19

Seyed Sobhan Mir Yoosefi will present his General Exam on May 2nd, 2019 at 10:45am in CS 401. The members of his committee are as follows: Yoram Singer (adviser), Robert Schapire, and Matt Weinberg Everyone is invited to attend his talk, and those faculty wishing to remain for the oral exam following are welcome to do so. His abstract and reading list follow below. Title: Reinforcement Learning with General Constraints Abstract: In some applications of RL, it's not easy to achieve the goal in mind only by designing a scalar reward function. In those tasks, it might be more appropriate to think of both constraints and reward. These constraints might help you to meet some safety criteria, shape the behavior of the agent, or encourage exploration and diversity. The previous works done on this topic are mostly limited to a specific type of constraints and they aim to achieve only one of the above. We introduce a new formulation of the problem which handles the general form of constraints; we are given an MDP in which instead of getting a scalar reward for our actions, we receive a vector measurement. Now the goal is to find a policy for which the expected vector measurement lies in a given convex target set. Given access to a planning oracle (scalar with no constraint), We show that we are able to give an algorithm which solves this general problem. Now we can aim for more than one of the goals the previous algorithm were dealing with. For example, we can meet the safety constraints and at the same time encourage exploration and diversity. Reading List: [ https://docs.google.com/document/d/1gyK7CSo3Fh99ABH8O6yNYtPY2U_DHW5wUcQ-iXT… | https://docs.google.com/document/d/1gyK7CSo3Fh99ABH8O6yNYtPY2U_DHW5wUcQ-iXT… ] Text Books: * Sutton, Richard S., and Andrew G. Barto. Reinforcement learning: An introduction . MIT press, 2018. * Chapters: 2-10,13 * Shalev-Shwartz, Shai, and Shai Ben-David. Understanding machine learning: From theory to algorithms . Cambridge university press, 2014. * Chapters: 2-6, 9, 10, 12, 14 Papers: * Syed, Umar, and Robert E. Schapire. "A game-theoretic approach to apprenticeship learning." Advances in neural information processing systems . 2008. * Blackwell, David. "An analog of the minimax theorem for vector payoffs." Pacific Journal of Mathematics 6.1 (1956): 1-8. * Abernethy, Jacob, Peter L. Bartlett, and Elad Hazan. "Blackwell approachability and no-regret learning are equivalent." Proceedings of the 24th Annual Conference on Learning Theory . 2011. * Hazan, E., Kakade, S. M., Singh, K., & Van Soest, A. (2018). Provably efficient maximum entropy exploration. arXiv preprint arXiv:1812.02690 . * Le, Hoang M., Cameron Voloshin, and Yisong Yue. "Batch Policy Learning under Constraints." arXiv preprint arXiv:1903.08738 (2019). * C. Tessler, D. J. Mankowitz, and S. Mannor. Reward constrained policy optimization. arXiv preprint arXiv:1805.11074 , 2018. * Agrawal, Shipra, and Nikhil R. Devanur. "Bandits with concave rewards and convex knapsacks." Proceedings of the fifteenth ACM conference on Economics and computation . ACM, 2014. * Mannor, Shie, and John N. Tsitsiklis. "Online learning with constraints." International Conference on Computational Learning Theory . Springer, Berlin, Heidelberg, 2006. * Abernethy, Jacob D., and Jun-Kun Wang. "On frank-wolfe and equilibrium computation." Advances in Neural Information Processing Systems . 2017.

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Linguang Zhang will present his FPO, "Learning and Deploying Local Features" on Monday, 5/6/2019 at 1pm in CS 402.
by Nicki Mahler 23 Apr '19

23 Apr '19

Linguang Zhang will present his FPO, "Learning and Deploying Local Features" on Monday, 5/6/2019 at 1pm in CS 402. The members of his committee are as follows: Szymon Rusinkiewicz (adviser); Readers: Thomas Funkhouser and Olga Russakovsky; Nonreaders: Adam Finkelstein and Jia Deng. A copy of his thesis is available upon request. Everyone is invited to attend his talk. The talk abstract follows below: Many computer vision applications including image matching, image-based reconstruction and localization rely on extracting and matching robust local features. A typical local feature pipeline first detects repeatable keypoints in the image (i.e., keypoint detector), and then computes a short vector to uniquely describe each keypoint (i.e., feature descriptor). Both the keypoint detector and the feature descriptor are conventionally hand-crafted based on what is intuitive to the designer. For example, corners or blobs are popular choices of keypoints, and the image gradient is a useful clue for descriptors. However, it is often dicult to define these principles to accommodate various applications. In this thesis, we study data-driven approaches which can more easily tailor the local feature pipeline for target applications. We start with a mobile robotics application that leverages local features extracted from ground texture images to achieve high-precision global localization. The second part of the thesis addresses the problem that existing keypoint detectors that are optimized for natural images su↵er from sub-optimal performance on texture images. We therefore learn a keypoint detector specifically for each type of texture using a deep neural network. Our detector automatically learns to identify keypoints that are distinctive in the target texture rather than relying on a set of pre-defined rules. Finally, we focus on a non-parametric approach for learning feature descriptors. Many well-performing local feature descriptors are trained using a triplet loss that includes a tunable margin, which limits its ability to generalize to other types of data and problems. We propose to replace the hard margin with a soft margin that self-tunes as learning progresses. To summarize, we first demonstrate through a novel visual-based localization system where a customized local feature pipeline is critical. Then, we tackle both the keypoint detector and the feature descriptor with generalizable data-driven approaches.

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Microsoft's Bill Buxton speaking Monday, April 29
by Emily Lawrence 23 Apr '19

23 Apr '19

Bill Buxton, Principal Research at Microsoft, will be talking about creativity, innovation and design, especially design research and technology. Monday, April 29th at 4:30pm in the Friend Center Convocation Room. Open to the public. RSVP: https://www.tfaforms.com/4734441 BIO A Principal Researcher at Microsoft Research, Bill has had a 40- year involvement in research, practice and commentary around design, innovation and human aspects of technology. Following a 20-year career as a professional musician, he morphed into a researcher and interaction designer, at the University of Toronto, Xerox PARC, Alias Research and SGI Inc. He has been awarded four honourary doctorates, is co-recipient of an Academy Award for Scientific and Technical Achievement, received an ACM/SIGCHI Lifetime Achievement Award, and is a Fellow of the ACM. Bill has published, lectured and consulted widely, and is an Adjunct Professor at the University of Toronto, and a Distinguished Professor of Industrial Design at the Technical University Eindhoven. Other than his family, mountains and rivers are his first love. For more information, see billbuxton.com TALK TITLE & ABSTRACT The Buxton-Microsoft Collection: On the Importance of the History of the Past in Shaping the History of the Future History, backed up by current data, tells us that what we perceive as rapid technological change is generally due to a large number of technologies evolving slowly. For example, the recent history of information and telecommunications technologies says that it takes about 20-30 years for a technology, once identified, to reach maturity (defined, for example, as becoming a $1B industry). That says, for example, that anything which is going to become a $1B industry in the next 5 years most likely already has a 15 year history - a history which is generally below the radar, is nevertheless discoverable by those who know how and where to look. Over the past 45 years I have accumulated a collection of gadgets that captures the history of technological growth. For you, the value may just be nostalgia. However, my hope is this. In this age where the things which we produce create such a strong cultural impact, can we really afford not to take advantage of the learnings of the past hidden in plain sight? Beth Ellen Jarvie Communication Coordinator Keller Center School of Engineering and Applied Science Princeton University ACE 25 Engineering Quadrangle Princeton, NJ 08544 609-258-1643

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Yixin Sun will present her Pre FPO, "Enhancing Anonymity Systems under Network and User Dynamics" on April 24, 2019 at 3pm in CS 402
by Nicki Mahler 22 Apr '19

22 Apr '19

Yixin Sun will present her Pre FPO, "Enhancing Anonymity Systems under Network and User Dynamics" on April 24, 2019 at 3pm in CS 402. The members of her committee are as follows: Prateek Mittal (reader), Nick Feamster (reader), Mung Chiang (advisor), Jennifer Rexford (non-reader), Ed Felten (non-reader) Everyone is invited to attend her talk. The talk title and abstract follow below. Title: Enhancing Anonymity Systems under Network and User Dynamics Abstract: Privacy on the Internet is eroding rapidly. Anonymity systems have been designed to protect the identity and privacy of users from untrusted destinations and third parties on the Internet. However, many anonymity systems assume that important system components, such as the network infrastructure and client location, are static. In practice, these components are highly dynamic and exhibit changes over time. In this dissertation, I exploit network and user dynamics to uncover new attacks in anonymity systems, and consequently build defenses to protect user anonymity from such new attacks. First, we present Raptor attacks, that can be launched by Autonomous Systems (ASes) to compromise user anonymity in the Tor network. AS-level adversaries can exploit the asymmetric nature of Internet routing and launch active routing attacks to observe user traffic and deanonymize users via traffic correlation analysis. We successfully demonstrate the attacks in the wild with 95% accuracy rate. Second, we design the Counter-Raptor defense to safeguard Tor against active routing attacks via a new Tor guard relay selection algorithm that incorporates the resilience of relays into consideration. We show that the algorithm successfully improves the security for Tor clients by up to 36% on average (up to 166% for certain clients). Finally, we present Tempest attack that exploits client mobility to compromise anonymity. Using experimental analysis on real-world datasets, we demonstrate that mobility degrades user privacy across a wide range of anonymity systems, including deployed systems such as Tor; path-selection protocols for Tor such as DeNASA and Counter-RAPTOR; and network-layer anonymity protocols for Internet routing such as HORNET.

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