Publications
Our teams aspire to make discoveries that impact everyone, and core to our approach is sharing our research and tools to fuel progress in the field
Our teams aspire to make discoveries that impact everyone, and core to our approach is sharing our research and tools to fuel progress in the field
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1 - 15 of 1416 publications
Preview abstract
Hashing is a fundamental operation in various computer sci-
ence applications. Despite the prevalence of specific key
formats like social security numbers, MAC addresses, plate
numbers, and URLs, hashing libraries typically treat them as
general byte sequences. This paper introduces a technique
for synthesizing specialized hash functions tailored to par-
ticular byte formats. The proposed code generation method
leverages three prevalent patterns: (i) fixed-length keys, (ii)
keys with common subsequences, and (iii) keys ranging on
predetermined sequences of bytes. The code generation pro-
cess involves two algorithms: one identifies relevant regular
expressions within key examples, and the other generates
specialized hash functions based on these expressions. This
approach, straightforward to implement, showcases improve-
ments over highly optimized hash function implementations.
Comparative analysis demonstrates that our synthetic func-
tions outperform counterparts in the C++ Standard Template
Library and the Google Abseil Library, achieving speedups
ranging from 2% to 11%, depending on the key format.
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Online Bidding under RoS Constraints without Knowing the Value
Sushant Vijayan
Swati Padmanabhan
The Web Conference (2025)
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We consider the problem of auto-bidding in online advertising from the perspective of a single advertiser. The goal of the advertiser is to maximize their value under the Return-on-Spend (RoS) constraint, with performance measured in terms of \emph{regret} against the optimal offline solution that knows all queries a priori. Importantly, the value of the item is \textit{unknown} to the bidder ahead of time. The goal of the bidder is to quickly identify the optimal bid, while simultaneously satisfying budget and RoS constraints. Using a simple UCB-style algorithm, we provide the first result which achieves optimal regret and constraint violation for this problem.
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We consider the Coalition Structure Learning (CSL) problem in multi-agent systems, motivated by the existence of coalitions in many real-world systems, e.g., trading platforms and auction systems. In this problem, there is a hidden coalition structure within a set of $n$ agents, which affects the behavior of the agents in games. Our goal is to actively design a sequence of games
for the agents to play, such that observations in these games can be used to learn the hidden coalition structure. In particular, we consider the setting where in each round, we design and present a game together with a strategy profile to the agents, and receive a multiple-bit observation -- for each agent, we observe whether or not they would like to deviate from the specified strategy in this given game. Our contributions are three-fold: First, we show that we can learn the coalition structure in $O(\log n)$ rounds if we are allowed to choose any normal-form game in each round, matching the information-theoretical lower bound, and the result can be extended to congestion games. Second, in a more restricted setting where we can only choose a graphical game with degree limit $d$, we develop an algorithm to learn the coalition structure in $O(n/d+\log d)$ rounds. Third, when we can only learn the coalition structure through running second-price auctions with personalized reserve prices, we show that the coalition structure can be learned in $O(c\log n)$ rounds, where $c$ is the size of the largest coalition.
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Improving simulation-based origin-destination demand calibration using sample segment counts data
Arwa Alanqary
Yechen Li
The 12th Triennial Symposium on Transportation Analysis conference (TRISTAN XII), Okinawa, Japan (2025)
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This paper introduces a novel approach to demand estimation that utilizes partial observations of segment-level track counts. Building on established simulation-based demand estimation methods, we present a modified formulation that integrates sample track counts as a regularization term. This approach effectively addresses the underdetermination challenge in demand estimation, moving beyond the conventional reliance on a prior OD matrix. The proposed formulation aims to preserve the distribution of the observed track counts while optimizing the demand to align with observed path-level travel times. We tested this approach on Seattle's highway network with various congestion levels. Our findings reveal significant enhancements in the solution quality, particularly in accurately recovering ground truth demand patterns at both the OD and segment levels.
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Preview abstract
Users of routing services like Apple Maps, Google Maps, and Waze frequently wonder why a given route is proposed. This question particularly arises when dynamic conditions like traffic and road closures cause unusual routes to be proposed. While many such dynamic conditions may exist in a road network at any time, only a small fraction of those conditions are typically relevant to a given user's route. In this work, we give a simple algorithm that identifies a small set of traffic-laden road segments that answer the following question: Which traffic conditions cause a particular shortest traffic-aware route to differ from the shortest traffic-free route? We theoretically and experimentally show that our algorithm generates small and interpretable answers to this question.
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Fast Tensor Completion via Approximate Richardson Iteration
Mehrdad Ghadiri
Yunbum Kook
Ali Jadbabaie
Proceedings of the 42nd International Conference on Machine Learning (2025), pp. 19248-19265
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We study tensor completion (TC) through the lens of low-rank tensor decomposition (TD). Many TD algorithms use fast alternating minimization methods, which solve highly structured linear regression problems at each step (e.g., for CP, Tucker, and tensor-train decompositions). However, such algebraic structure is lost in TC regression problems, making direct extensions unclear. To address this, we propose a lifting approach that approximately solves TC regression problems using structured TD regression algorithms as blackbox subroutines, enabling sublinear-time methods. We theoretically analyze the convergence rate of our approximate Richardson iteration based algorithm, and we demonstrate on real-world tensors that its running time can be 100x faster than direct methods for CP completion.
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Origin-destination travel demand estimation: an approach that scales worldwide, and its application to five metropolitan highway networks
Christopher Bian
Yechen Li
Willa Ng
Bin Yan
Janny Zhang
2025
Preview abstract
Estimating Origin-Destination (OD) travel demand is vital for effective urban planning
and traffic management. Developing universally applicable OD estimation
methodologies is significantly challenged by the pervasive scarcity of high-fidelity traffic
data and the difficulty in obtaining city-specific prior OD estimates (or seed ODs), which
are often prerequisite for traditional approaches. Our proposed method directly
estimates OD travel demand by systematically leveraging aggregated, anonymized
statistics from Google Maps Traffic Trends, obviating the need for conventional census
or city-provided OD data. The OD demand is estimated by formulating a single-level,
one-dimensional, continuous nonlinear optimization problem with nonlinear equality
and bound constraints to replicate highway path travel times. The method achieves
efficiency and scalability by employing a differentiable analytical macroscopic network
model. This model by design is computationally lightweight, distinguished by its
parsimonious parameterization that requires minimal calibration effort and its capacity
for instantaneous evaluation. These attributes ensure the method's broad applicability
and practical utility across diverse cities globally. Using segment sensor counts from
Los Angeles and San Diego highway networks, we validate our proposed approach,
demonstrating a two-thirds to three-quarters improvement in the fit to segment count
data over a baseline. Beyond validation, we establish the method's scalability and
robust performance in replicating path travel times across diverse highway networks,
including Seattle, Orlando, Denver, Philadelphia, and Boston. In these expanded
evaluations, our method not only aligns with simulation-based benchmarks but also
achieves an average 13% improvement in it's ability to fit travel time data compared to
the baseline during afternoon peak hours.
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Day-of-the-week Awareness in Time of Day Breakpoints for Traffic Light Plans
Ori Rottenstreich
Eliav Buchnik
Shai Ferster
Tom Kalvari
Ron Tsibulsky
Danny Veikherman
Jack Haddad
2025
Preview abstract
Time-of-day breakpoints (TODs) refer to the times over the day in which the plan of a traffic light is changed. Traditionally, TODs are selected jointly for all weekdays (Monday-Friday), typically with additional TODs dedicated to weekends. In this paper, we present an alternative approach motivated by traffic characteristics that can differ among the weekdays Monday-Friday and consider TODs which are day-of-the-week aware. The traffic-aware approach studies similarities among days and computes TODs that can be shared among days with similar characteristics but can also have other forms for weekdays with unique characteristics. Based on traffic properties derived from anonymized trajectories, we apply the new methodology to compute time-of-day breakpoints that are day-of-the-week aware in the city of Rio de Janeiro, Brazil and estimate the impact of the new methodology.
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Preview abstract
This paper presents a novel framework for optimizing capacitor selection in electronic design using multi-objective linear and non-linear constrained optimization techniques. We demonstrate the effectiveness of this approach in minimizing cost and board area while meeting critical performance requirements.
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Preview abstract
Julia's strength in mathematical computation and high performance makes it a popular choice across scientific fields, mostly due to its focus on mathematics in a broad sense and execution performance. It is a language of choice to implement new numerical algorithms, but it really shines in modelling for optimisation thanks to JuMP.jl and MathOptInterface.jl.
These libraries are, first and foremost, made for mathematical optimisation (linear, mixed-integer, conic, etc.), yet they are now generic enough to support more paradigms, such as constraint programming. This talk will introduce the basic principles behind the current implementation of JuMP.jl and explain why and how they are very good matches for modelling using constraint programming… and solving using any kind of mixed-integer-programming solver.
Constraint-programming solvers can also be implemented using linear programming, in a great collaboration between discrete and continuous optimisation. This talk will briefly explain the connection and its implementation in Google’s CP-SAT, a leading, award-winning constraint solver that uses linear programs in its solving process — a solver that will soon be available in Julia too.
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Preview abstract
Google has a long tradition of open-source software, which encompasses the field of operations research with OR-Tools. In development since 2008, it offers several solvers useful to many OR practitioners:
- PDLP, a revolutionary first-order linear solver that is reshaping the landscape of linear optimisation;
- CP-SAT, an award-winning constraint-programming solver;
- Glop, an accurate linear solver;
- Routing, a vehicle routing solver underpinning Google Maps Platform Route Optimization.
OR-Tools has long had its features accessible from other languages: the core algorithms are implemented in C++ for performance, but users can tap into them in Python, Java, C#, or Go.
It is recently available in Julia too, with a current focus on the linear and constraint solvers, either locally or remotely.
We provide a wrapper for our solvers that brings them to JuMP.jl through MathOptInterface.jl.
This tutorial will walk you through the features of OR-Tools and its solvers, then show examples of using OR-Tools from within Julia, either through JuMP or a lower-level interface.
We will also share our experience of C++-Julia interop.
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Governing Innovation: Google's SOX Controls for AI/ML in Financial Systems
Eshan Bhatt
Ivey Publishing, Ivey Business School, Western University, London, Ontario, Canada (2025)
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The integration of Artificial Intelligence (AI) and Machine Learning (ML) in financial systems is transforming risk modeling, forecasting, and operational efficiency. However, the adoption of these technologies introduces new risks to financial reporting. This business case outlines how organizations can design and implement SOX-compliant IT controls tailored to AI/ML use cases in Finance, aligning with Internal Control over Financial Reporting (ICFR) requirements and regulatory expectations.
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Protecting user privacy in financial transactions is desirable, yet in the classical world it is effectively impossible without hardware assumptions. Most existing quantum money schemes also fail to guarantee anonymity. We introduce a construction of single-use quantum tokens that give users the ability to detect whether the issuing authority is tracking them, for which we prove unconditional security. Our tokens do not require quantum communication from the users themselves, making them relatively practical to deploy.
We discuss potential applications including one-time payment tokens, anonymous one-time pads and voting.
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Preview abstract
JuMP and MathOptInterface.jl give access to many solvers, both very common in the industry and more specialised. Google offers its own in-house solvers as part of the open-source package OR-Tools: Glop, a simplex solver; CP-SAT, an award-winning constraint-programming solver; PDLP, a first-order solver for large-scale linear programming.
ORTools.jl is a recent package that gives access to these solvers through MathOptInterface.jl. It supports both local and remote use, meaning that users do not need a local installation to solve linear and integer problems thanks to Google Cloud. More recently, ORTools.jl started offering a native interface for constraint programming building upon the work in MathOptInterface.jl.
However, OR-Tools have more than this to offer, including a scalable routing solver for large-scale VRPs or state-of-the-art set-cover solver. MathOptInterface.jl does not yet propose an interface for these problems and we would like to gauge the community’s interest in these specific solvers.
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Preview abstract
We study the problem of learning the optimal item pricing for a unit-demand buyer with independent item values, and we have query access to the underlying value distributions. We consider two common query model in the literature: the “sample complexity” model where we can obtain a sample of each item value, and the “pricing query complexity” model where we can set a price to each item and obtain a binary signal on whether the sampled value of the item is greater than our proposed price. In this work we give nearly tight sample complexity and pricing query complexity of the problem.
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