## About

241

Publications

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Introduction

Additional affiliations

January 2006 - present

January 1992 - December 2011

January 1988 - present

## Publications

Publications (241)

Maximizing the revenue from selling two or more goods has been shown to require the use of $nonmonotonic$ mechanisms, where a higher-valuation buyer may pay less than a lower-valuation one. Here we show that the restriction to $monotonic$ mechanisms may not just lower the revenue, but may in fact yield only a $negligible$ $fraction$ of the maximal...

Using a unique pedagogical approach, this text introduces mathematical logic by guiding students in implementing the underlying logical concepts and mathematical proofs via Python programming. This approach, tailored to the unique intuitions and strengths of the ever-growing population of programming-savvy students, brings mathematical logic into t...

Using a unique pedagogical approach, this text introduces mathematical logic by guiding students in implementing the underlying logical concepts and mathematical proofs via Python programming. This approach, tailored to the unique intuitions and strengths of the ever-growing population of programming-savvy students, brings mathematical logic into t...

Using a unique pedagogical approach, this text introduces mathematical logic by guiding students in implementing the underlying logical concepts and mathematical proofs via Python programming. This approach, tailored to the unique intuitions and strengths of the ever-growing population of programming-savvy students, brings mathematical logic into t...

In the early 20th century, Pigou observed that imposing a marginal cost tax on the usage of a public good induces a socially efficient level of use as an equilibrium. Unfortunately, such a “Pigouvian” tax may also induce other, socially inefficient, equilibria. We observe that this social inefficiency may be unbounded, and study whether alternative...

In the early $20^{th}$ century, Pigou observed that imposing a marginal cost tax on the usage of a public good induces a socially efficient level of use as an equilibrium. Unfortunately, such a "Pigouvian" tax may also induce other, socially inefficient, equilibria. We observe that this social inefficiency may be unbounded, and study whether altern...

Consider a monopolist selling n items to an additive buyer whose item values are drawn from independent distributions F1,F2,…,Fn possibly having unbounded support. Unlike in the single-item case, it is well known that the revenue-optimal selling mechanism (a pricing scheme) may be complex, sometimes requiring a continuum of menu entries. Also known...

It is widely observed that individuals prefer to interact with others who are more similar to them (this phenomenon is termed homophily). This similarity manifests itself in various ways such as beliefs, values and education. Thus, it should not come as a surprise that when people make hiring choices, for example, their similarity to the candidate...

We study competitive equilibrium in the canonical Fisher market model, but with indivisible goods. In this model, every agent has a budget of artificial currency with which to purchase bundles of goods. Equilibrium prices match between demand and supply---at such prices, all agents simultaneously get their favorite within-budget bundle, and the mar...

In 1976, Knuth asked whether the worst-case running-time of the Gale-Shapley algorithm for the Stable Marriage Problem can be improved when non-sequential access to the input is allowed. Partial negative answers were given by Ng and Hirschberg and as part of Segal's general communication-complexity analysis. We give a far simpler, yet significantly...

We study a communication variant of local search. There is some fixed, commonly known graph G. Alice holds fA and Bob holds fB, both are functions that specify a value for each vertex. The goal is to find a local maximum of fA+fB with respect to G, i.e., a vertex v for which (fA+fB)(v)≥ (fA+fB)(u) for each neighbor u of v.
Our main result is that f...

We describe our experience with designing and running a matching market for the Israeli "Mechinot" gap-year programs. The main conceptual challenge in the design of this market was the rich set of diversity considerations, which necessitated the development of an appropriate preference-specification language along with corresponding choice-function...

We introduce a `concrete complexity' model for studying algorithms for matching in bipartite graphs. The model is based on the "demand query" model used for combinatorial auctions. Most (but not all) known algorithms for bipartite matching seem to be translatable into this model including exact, approximate, sequential, parallel, and online ones. A...

We describe our experience with designing and running a matching market for the Israeli "Mechinot" gap-year programs. The main conceptual challenge in the design of this market was the rich set of diversity considerations, which necessitated the development of an appropriate preference-specification language along with corresponding choice-function...

Two food banks catering to populations of different sizes with different needs must divide among themselves a donation of food items. What constitutes a "fair" allocation of the items among them?
Competitive equilibrium from equal incomes (CEEI) is a classic solution to the problem of fair and efficient allocation of goods among equally entitled ag...

Border’s theorem gives an intuitive linear characterization of the feasible interim allocation rules of a Bayesian single-item environment, and it has several applications in economic and algorithmic mechanism design. All known generalizations of Border’s theorem either restrict attention to relatively simple settings or resort to approximation. Th...

We study revenue maximization by deterministic mechanisms for the simplest case for which Myerson's characterization does not hold: a single seller selling two items, with independently distributed values, to a single additive buyer. We prove that optimal mechanisms are submodular and hence monotone. Furthermore, we show that in the IID case, optim...

We study revenue maximization by deterministic mechanisms for the simplest case for which Myerson's characterization does not hold: a single seller selling two items, with independently distributed values, to a single additive buyer. We prove that optimal mechanisms are submodular and hence monotone. Furthermore, we show that in the IID case, optim...

We study the following communication variant of local search. There is some fixed, commonly known graph $G$. Alice holds $f_A$ and Bob holds $f_B$, both are functions that specify a value for each vertex. The goal is to find a local maximum of $f_A+f_B$ with respect to $G$, i.e., a vertex $v$ for which $(f_A+f_B)(v)\geq (f_A+f_B)(u)$ for every neig...

We study the necessity of interaction between individuals for obtaining approximately efficient economic allocations. We view this as a formalization of Hayek's classic point of view that focuses on the information transfer advantages that markets have relative to centralized planning. We study two settings: combinatorial auctions with unit demand...

We suggest a general method for inferring players' values from their actions in repeated games. The method extends and improves upon the recent suggestion of (Nekipelov et al., EC 2015) and is based on the assumption that players are more likely to exhibit sequences of actions that have lower regret. We evaluate this "quantal-regret" method on two...

We consider a price competition between two sellers of perfect-complement goods. Each seller posts a price for the good it sells, but the demand is determined according to the sum of prices. This is a classic model by Cournot (1838), who showed that in this setting a monopoly that sells both goods is better for the society than two competing seller...

Using data obtained in a controlled ad-auction experiment that we ran, we evaluate the regret-based approach to econometrics that was recently suggested by Nekipelov, Syrgkanis, and Tardos (EC 2015). We found that despite the weak regret-based assumptions, the results were (at least) as accurate as those obtained using classic equilibrium-based ass...

We study competitive equilibria in the basic Fisher market model, but with indivisible goods. Such equilibria fail to exist in the simplest possible market of two players with equal budgets and a single good, yet this is a knife's edge instance as equilibria exist once budgets are not precisely equal. Is non-existence of equilibria also a knife-edg...

Cloud computing has reached significant maturity from a systems perspective, but currently deployed solutions rely on rather basic economics mechanisms that yield suboptimal allocation of the costly hardware resources. In this paper we present Economic Resource Allocation (ERA), a complete framework for scheduling and pricing cloud resources, aimed...

We suggest a general method for inferring players' values from their actions in repeated games. The method extends and improves upon the recent suggestion of (Nekipelov et al., EC 2015) and is based on the assumption that players are more likely to exhibit sequences of actions that have lower regret. We evaluate this "quantal regret" method on two...

We study correlated equilibria and coarse equilibria of simple first-price single-item auctions in the simplest auction model of full information. Nash equilibria are known to always yield full efficiency and a revenue that is at least the second-highest value. We prove that the same is true for all correlated equilibria, even those in which agents...

We consider a simple simultaneous first price auction for two identical items in a complete information setting. Our goal is to analyze this setting for a simple, yet highly interesting, AND-OR game, where one agent is single minded and the other is unit demand. We find a mixed equilibrium of this game and show that every other equilibrium admits t...

We present a polynomial-time algorithm that, given samples from the unknown valuation distribution of each bidder, learns an auction that approximately maximizes the auctioneer's revenue in a variety of single-parameter auction environments including matroid environments, position environments, and the public project environment. The valuation dist...

Using data obtained in a controlled ad-auction experiment that we ran, we evaluate the regret-based approach to econometrics that was recently suggested by Nekipelov, Syrgkanis, and Tardos (EC 2015). We found that despite the weak regret-based assumptions, the results were (at least) as accurate as those obtained using classical equilibrium-based a...

We consider a network of sellers, each selling a single product, where the graph structure represents pair-wise complementarities between products. We study how the network structure affects revenue and social welfare of equilibria of the pricing game between the sellers. We prove positive and negative results, both of "Price of Anarchy" and of "Pr...

We consider a monopolist that is selling $n$ items to a single additive buyer, where the buyer's values for the items are drawn according to independent distributions $F_1, F_2,\ldots,F_n$ that possibly have unbounded support. It is well known that - unlike in the single item case - the revenue-optimal auction (a pricing scheme) may be complex, som...

We study correlated equilibria and coarse equilibria of simple first-price single-item auctions in the simplest auction model of full information. Nash equilibria are known to always yield full efficiency and a revenue that is at least the second-highest value. We prove that the same is true for all correlated equilibria, even those in which agents...

A natural measure of smoothness of a Boolean function is its sensitivity (the largest number of Hamming neighbors of a point which differ from it in function value). The structure of smooth or equivalently low-sensitivity functions is still a mystery. A well-known conjecture states that every such Boolean function can be computed by a shallow decis...

Mechanism design is a subfield of game theory that aims to design games whose equilibria have desired properties such as achieving high efficiency or high revenue. Algorithmic mechanism design is a subfield that lies on the border of mechanism design and computer science and deals with mechanism design in algorithmically complex scenarios that are...

The Gale-Shapley algorithm for the Stable Marriage Problem is known to take θ (n2) steps to find a stable marriage in the worst case, but only θ (n log n) steps in the average case (with n women and n men). In 1976, Knuth asked whether the worst-case running time can be improved in a model of computation that does not require sequential access to t...

A natural measure of smoothness of a Boolean function is its sensitivity (the
largest number of Hamming neighbors of a point which differ from it in function
value). The structure of smooth or equivalently low-sensitivity functions is
still a mystery. A well-known conjecture states that every such Boolean
function can be computed by a shallow decis...

Border's theorem gives an intuitive linear characterization of the feasible
interim allocation rules of a Bayesian single-item environment, and it has
several applications in economic and algorithmic mechanism design. All known
generalizations of Border's theorem either restrict attention to relatively
simple settings, or resort to approximation. T...

We continue the study of welfare maximization in unit-demand (matching)
markets, in a distributed information model where agent's valuations are
unknown to the central planner, and therefore communication is required to
determine an efficient allocation. Dobzinski, Nisan and Oren (STOC'14) showed
that if the market size is $n$, then $r$ rounds of i...

The Gale-Shapely algorithm for the Stable Marriage Problem is known to take
$\Theta(n^2)$ steps to find a stable marriage in the worst case, but only
$\Theta(n \log n)$ steps in the average case (with $n$ women and $n$ men). In
1976, Knuth asked whether the worst-case running time can be improved in a
model of computation that does not require sequ...

We performed controlled experiments of human participants in a continuous sequence of ad auctions, similar to those used by Internet companies. The goal of the research was to understand users' strategies in making bids. We studied the behavior under two auction types: (1) the Generalized Second-Price (GSP) auction and (2) the Vickrey--Clarke--Grov...

We consider (approximate) revenue maximization in mechanisms where the distribution on input valuations is given via “black box” access to samples from the distribution. We analyze the following model: a single agent, m outcomes, and valuations represented as m-dimensional vectors indexed by the outcomes and drawn from an arbitrary distribution pre...

We consider a single buyer with a combinatorial preference that would like to purchase related products and services from different vendors,where each vendor supplies exactly one product. We study the general case where subsets of products can be substitutes as well as complementary and analyze the game that is induced on the vendors, where a vendo...

We study the necessity of interaction between individuals for obtaining
approximately efficient allocations. The role of interaction in markets has
received significant attention in economic thinking, e.g. in Hayek's 1945
classic paper.
We consider this problem in the framework of simultaneous communication
complexity. We analyze the amount of simu...

Central results in economics guarantee the existence of efficient equilibria for various classes of markets. An underlying assumption in early work is that agents are price-takers, i.e., agents honestly report their true demand in response to prices. A line of research in economics, initiated by Hurwicz (1972), is devoted to understanding how such...

We consider the complexity of finding a Correlated Equilibrium in an n-player
game in a model that allows the algorithm to make queries for players'
utilities at pure strategy profiles. Many randomized regret-matching dynamics
are known to yield an approximate correlated equilibrium quickly: in time that
is polynomial in the number of players, the...

There are a number of domains where agents must collectively form a network in the face of the following trade-off: each agent receives benefits from the direct links it forms to others, but these links expose it to the risk of being hit by a cascading ...

We study scenarios where multiple sellers of a homogeneous good compete on
prices, where each seller can only sell to some subset of the buyers.
Crucially, sellers cannot price-discriminate between buyers. We model the
structure of the competition by a graph (or hyper-graph), with nodes
representing the sellers and edges representing populations of...

We consider the menu size of auctions as a measure of auction complexity and
study how it affects revenue. Our setting has a single revenue-maximizing
seller selling two or more heterogeneous items to a single buyer whose private
values for the items are drawn from a (possibly correlated) known distribution,
and whose valuation is additive over the...

We consider a simple simultaneous first price auction for multiple items in a
complete information setting. Our goal is to completely characterize the mixed
equilibria in this setting, for a simple, yet highly interesting, {\tt
AND}-{\tt OR} game, where one agent is single minded and the other is unit
demand.

We characterize methods of dividing a cake between two bidders in a way that
is incentive-compatible and Pareto-efficient. In our cake cutting model, each
bidder desires a subset of the cake (with a uniform value over this subset),
and is allocated some subset. Our characterization proceeds via reducing to a
simple one-dimensional version of the pr...

In combinatorial auctions, a large number of items are auctioned concurrently and bidders are allowed to express preferences on bundles of items. This is preferable to selling each item separately when there are dependencies between the different items, This problem has direct applications, may be viewed as a general abstraction of complex resource...

We study a combinatorial variant of the classical principal-agent model. In our setting a principal wishes to incentivize a team of strategic agents to exert costly effort on his behalf. Agentsʼ actions are hidden and the principal observes only the outcome of the team, which depends stochastically on the complex combinations of the efforts by the...

We consider the age-old problem of allocating items among different agents in
a way that is efficient and fair. Two papers, by Dolev et al. and Ghodsi et
al., have recently studied this problem in the context of computer systems.
Both papers had similar models for agent preferences, but advocated different
notions of fairness. We formalize both fai...

Myerson's classic result provides a full description of how a seller can maximize revenue when selling a single item. We address the question of revenue maximization in the simplest possible multi-item setting: two items and a single buyer who has independently distributed values for the items, and an additive valuation. In general, the revenue ach...

Display advertisements on the web are sold via ad exchanges that use real
time auction. We describe the challenges of designing a suitable auction, and
present a simple auction called the Optional Second Price (OSP) auction that is
currently used in Doubleclick Ad Exchange.

Motivated by the problem of querying and communicating bidders' valuations in combinatorial auctions, we study how well different classes of set functions can be sketched. More formally, let f be a function mapping subsets of some ground set [n] to the non-negative real numbers. We say that f' is an α-sketch of f if for every set S, the value f'(S)...

With the recent technological feasibility of electronic commerce over the
Internet, much attention has been given to the design of electronic markets for
various types of electronically-tradable goods. Such markets, however, will
normally need to function in some relationship with markets for other related
goods, usually those downstream or upstrea...

Often, in both computerized settings and economics settings, the prescribed behavior for participants is to repeatedly "best respond" to each others' actions. We aim to understand when such myopic "local rationality" is also "globally rational", i.e., when is it best for a player, given that the others are repeatedly best-responding, to also repeat...

The Gibbard-Satterthwaite theorem states that every non-dictatorial election
rule among at least three alternatives can be strategically manipulated. We
prove a quantitative version of the Gibbard-Satterthwaite theorem: a random
manipulation by a single random voter will succeed with a non-negligible
probability for any election rule among three al...

We study markets of indivisible items in which price-based (Walrasian)
equilibria often do not exist due to the discrete non-convex setting. Instead
we consider Nash equilibria of the market viewed as a game, where players bid
for items, and where the highest bidder on an item wins it and pays his bid. We
first observe that pure Nash-equilibria of...

We consider computationally-efficient incentive-compatible mechanisms that use the VCG payment scheme, and study how well they can approximate the social welfare in auc- tion settings. We present a novel technique for setting lower bounds on the approximation ratio of this type of mecha- nisms. Specifically, for combinatorial auctions among sub- mo...

Under many distributed protocols, the prescribed behavior for participants is to behave greedily, i.e., to repeatedly "best respond" to the others' actions. We present recent work (Proc. ICS'11) where we tackle the following general question: "When is it best for a long-sighted participant to adhere to a distributed greedy protocol?". We take a gam...

We present a new framework for auction design and analysis that we term "best-response auctions". We use this framework to show that the simple and myopic best-response dynamics converge to the VCG outcome and are incentive compatible in several well-studied auction environments (Generalized Second Price auctions, and auctions with unit-demand bidd...

Under many protocols—in computerized settings and in economics settings—participants repeatedly "best respond" to each others' actions until the system "converges" to an equilibrium point. We ask when does such myopic "local rationality" imply "global rationality", i.e., when is it best for a player, given that the others are repeatedly best-respon...

In many real-world settings, strategic agents are instructed to follow best-reply dynamics. Indeed, many computational protocols are based on such repeated greedy interactions. Such settings give rise to a natural question, that has received very little attention: Is it in the best interest of the strategic agents to follow best-reply dynamics? Tha...

We study the inherent limitations of natural widely-used classes of ascending combinatorial auctions. Specifically, we show that ascending combinatorial auctions that do not use both non-linear prices and personalized prices cannot achieve social efficiency with general bidder valuations. We also show that the loss of efficiency can be severe and t...

We exhibit incentive compatible multi-unit auctions that are not affine maximizers (i.e. are not of the VCG family) and yet approximate the social welfare to within a factor of $1+\epsilon$. For the case of two-item two-bidder auctions we show that this family of auctions, termed triage mechanisms, are the only scalable ones that give an approximat...

We present an incentive-compatible polynomial-time approximation scheme for multi-unit auctions with general k-minded player valuations. The mechanism fully optimizes over an appropriately chosen sub-range of possible allocations and then uses VCG payments over this sub-range. We show that obtaining a fully polynomial-time incentive-compatible appr...

We exhibit three approximation algorithms for the allocation problem in combinatorial auctions with complement free bidders. The running time of these algorithms is polynomial in the number of items $m$ and in the number of bidders n, even though the "input size" is exponential in m. The first algorithm provides an O(log m) approximation. The secon...

This talk will describe the auction that Google uses for allocation and pricing of TV ads. The talk describes the actual system and puts it in proper theoretical context.

K. Roberts’ theorem from 1979 [Aggregation and revelation of preferences, 1st Eur. Summer Workshop Econ. Soc., Paris 1977, 321–348 (1979; Zbl 0429.90009)] states that the only incentive compatible mechanisms over a full domain and range of at least 3 are weighted variants of the VCG mechanism termed affine maximizers. Roberts’ proof is somewhat “ma...

This paper studies a setting where a principal needs to mo- tivate teams of agents whose efiorts lead to an outcome that stochas- tically depends on the combination of agents' actions, which are not directly observable by the principal. In (1) we suggest and study a basic \combinatorial agency" model for this setting. In this paper we expose a some...

This talk describes the auction system used by Google for allocation and pricing of TV ads. It is based on a simultaneous ascending auction, and has been in use since September 2008.

This document describes the auction system used by Google for allocation and pricing of TV ads. It is based on a simultaneous
ascending auction, and has been in use since September 2008.

We describe a synthesis course that provides a hands-on treatment of many hardware and software topics learned in computer science (CS) programs. Using a modular series of twelve projects, we walk the students through the gradual construction of a simple hardware platform and a modern software hierarchy, yielding a basic yet powerful computer syste...

Roberts (Aggregation and Revelation of Preferences. Papers presented at the 1st European Summer Workshop of the Econometric
Society, pp. 321–349. North-Holland, 1979) showed that every social choice function that is ex-post implementable in private
value settings must be weighted VCG, i.e. it maximizes the weighted social welfare. This paper provid...

We study the computational power and limitations of iterative combinatorial auctions. Most existing iterative combinatorial auctions are based on repeatedly suggesting prices for bundles of items, and querying the bidders for their ``demand'' under these prices. We prove several results regarding such auctions that use a polynomial number of demand...

This talk will describe the auction that Google uses for allocation and pricing of TV ads. The talk describes the actual system and puts it in proper theoretical context.

In many real-world settings (e.g., interdomain routing in the Internet) strategic agents are instructed to follow best-reply
dynamics in asynchronous environments. In such settings players learn of each other’s actions via update messages that can
be delayed or even lost. In particular, several players might update their actions simultaneously, or...

The Gibbard-Satterthwaite theorem states that every non-trivial voting method among at least 3 alternatives can be strategically manipulated. We prove a quantitative version of the Gibbard-Satterthwaite theorem: a random manipulation by a single random voter will succeed with non-negligible probability for every neutral voting method among 3 altern...

When attempting to design a truthful mechanism for a computationally hard problem such as combinatorial auctions, one is faced with the problem that most efficiently computable heuristics can not be embedded in any truthful mechanism (e.g. VCG-like payment rules will not ensure truthfulness).
We develop a set of techniques that allow constructing...

## Projects

Project (1)

General techniques for transforming randomized algorithms into deterministic algorithms