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Rica Gonen

Publications and source records attributed to Rica Gonen.

14 recordsLinked to original sources

Detecting Collusion in Peer Review: Drawing Inspiration from VCG Principle

The peer-review process, the bedrock of scientific advancement, is increasingly undermined by sophisticated collusion rings that systematically manipulate review outcomes to favor in-group members. While existing detection methods struggle to untangle obfuscated social ties in explicit co-authorship graphs, we introduce a new direction: Exclusion Based Anomaly Detection. Similar to the way VCG auctions work, we formally measure the marginal influence of suspected reviewer groups, exposing their signature even when explicit social graphs are hidden. To apply this at scale without prior knowledge of colluding groups, we introduce the Embedding Based Discovery Framework, which leverages continuous semantic embeddings to isolate latent collusive communities directly from their semantic profile, bypassing the adversarial limitations of explicit network analysis. Unlike traditional heuristic-based approaches, our framework functions as an automated auditor, requiring no prior knowledge of group membership. It achieves this by executing a decoupled search across independent diagnostic algorithms and combining their findings into distinct consensus formations, allowing organizers to dynamically balance detection precision and recall. Evaluating our technique with large-scale datasets (based on ICLR 2021) shows our method's capacity to identify both overt and subtle adversarial tactics with high sensitivity and strict Family-Wise Error Rate (FWER) control, effectively providing conference organizers with a scalable, robust, and privacy-preserving tool to secure the scientific integrity of academic publishing.

cs.GT

The Degree of Strategy-Proofness for Risk-Averse Committee Selection

The classic notion of strategyproofness implicitly assumes that a manipulating agent either possesses complete knowledge of what all other agents are going to report, or is willing to take the risk and act as if they know these reports. To capture the profound uncertainty of real-world voters, recent work introduced \emph{risk-avoiding truthfulness (RAT)} and the \emph{RAT-degree}, which quantifies the exact number of known reports required for a manipulation to be strictly safe. While the RAT-degree has been analyzed in settings such as single-winner elections, its implications for multi-winner voting remain unexplored. In this paper, we bridge this gap by extending the RAT-degree framework to approval-based committee (ABC) selection, focusing initially on the prominent Proportional Approval Voting (PAV) rule. We establish tight bounds on its susceptibility to safe subset manipulations, proving that PAV is immune to superset risk-avoiding manipulations given knowledge of at most $f = \lfloor \frac{n}{k+1} \rfloor - 1$ voters, but vulnerable when $f = \lceil \frac{n}{k} \rceil$. Recognizing that this degree of immunity may be insufficient in practice, we explore how to enhance strategic robustness by relaxing the proportionality requirement. We introduce a novel parameterized generalization of PAV, the family of $d$-RPAV rules, which encapsulates this inherent trade-off: a higher parameter $d$ yields stronger truthfulness and strategic robustness at the expense of weaker, relaxed proportionality guarantees. Specifically, we establish a generalized tight lower bound, proving that $d$-RPAV is completely immune to safe manipulation given knowledge of at most $f = \lfloor \frac{dn}{k+2d-1} \rfloor - 1$ voters.

cs.GT

What Are People's Actual Utility Functions in Budget Aggregation?

Budget aggregation is a process in which citizens vote by declaring their individual ideal budget allocation, and a pre-determined rule aggregates all votes into a single outcome. Recent theoretical work has proposed various aggregation rules, along with impossibility results for satisfying desirable axioms simultaneously. These analyses rely on assumptions about how voters evaluate non-ideal allocations, yet such assumptions have not been empirically validated on human subjects. We present a framework for empirically testing hypotheses about human utility functions using simple pairwise comparisons. We introduce a modular, open-source polling system that, after eliciting a subject's ideal allocation, presents carefully generated pairs of non-ideal alternatives. Different pair-generation algorithms allow testing various properties of utility functions. Using this framework, we conduct polls with hundreds of participants. The results show that standard utility models, including $\ell_1$, $\ell_2$, and Leontief, fail to capture human preferences, as very few participants behave consistently with any single model. In contrast, we find strong empirical support for more general properties, such as star-shaped, multi-dimensional single-peaked, and peak-linear preferences. We also find that most participants exhibit asymmetries both with respect to sign (gains vs. losses) and issue, contradicting any utility model based on an $\ell_p$ metric. These findings suggest that developing practical budget-aggregation mechanisms requires more flexible models of human utility functions.

cs.GT

The Min Max Average Cycle Weight Problem

When an old apartment building is demolished and rebuilt, how can we fairly redistribute the new apartments to minimize envy among residents? We reduce this question to a combinatorial optimization problem called the *Min Max Average Cycle Weight* problem. In that problem we seek to assign objects to agents in a way that minimizes the maximum average weight of directed cycles in an associated envy graph. While this problem reduces to maximum-weight matching when starting from a clean slate (achieving polynomial-time solvability), we show that this is not the case when we account for preexisting conditions, such as residents' satisfaction with their original apartments. Whether the problem is polynomial-time solvable in the general case remains an intriguing open problem.

cs.DS

Fair Allocation with Money: What is Your Objective?

When allocating indivisible items, there are various ways to use monetary transfers for eliminating envy. Particularly, one can apply a balanced vector of transfer payments, or charge each agent a positive amount, or -- contrarily -- give each agent a positive amount as a ``subsidy''. In each model, one can aim to minimize the amount of payments used; this aim translates into different optimization objectives in each setting. This note compares the various models, and the relations between upper and lower bounds for these objectives.

cs.GT

Fair Allocation of Improvements: When Old Endowments Shape New Assignments

This work is motivated by a common urban renewal process called Reconstruct and Divide. It involves the demolition of old buildings and the construction of new ones. Original homeowners are compensated with upgraded apartments, while surplus units are sold for profit, so theoretically it is a win-win project for all parties involved. However, many Reconstruct and Divide projects are withheld or delayed due to disagreements over the assignment of new apartments, claiming they are not fair. The goal of this research is to develop algorithms for envy-free assignment of the new apartments, possibly using monetary payments to reduce envy. In contrast to previous works on envy-free assignment, in our setting the envy depends also on the value of the old apartments, as people with more valuable old apartments expect to get more valuable new apartments. This presents two challenges. First, in some cases, no assignment and payment-vector satisfy the common fairness notions of envy-freeness and proportionality. Hence, we focus on minimizing the envy and the disproportionality (the distance between an agent's value and their proportional share). We present a strongly polynomial-time algorithm that, for a given assignment, finds a payment vector that minimizes the maximum pairwise-envy. We also present a strongly polynomial-time algorithm that computes an assignment and payment-vector that together minimize the maximum disproportionality. Second, directly asking the agents for their subjective valuations for their old apartments is infeasible, as it is a dominant strategy for them to report very high values for their old apartments. We introduce a novel method to elicit agents' valuations indirectly. Using this method, we identify conditions under which our Minimum Disproportionality algorithm is risk-averse truthful.

cs.GT

Whoever Said Money Won't Solve All Your Problems? Weighted Envy-free Allocation with Subsidy

We explore solutions for fairly allocating indivisible items among agents assigned weights representing their entitlements. Our fairness goal is weighted-envy-freeness (WEF), where each agent deems their allocated portion relative to their entitlement at least as favorable as any others relative to their own. Often, achieving WEF necessitates monetary transfers, which can be modeled as third-party subsidies. The goal is to attain WEF with bounded subsidies. Previous work relied on characterizations of unweighted envy-freeness (EF), that fail in the weighted setting. This makes our new setting challenging. We present polynomial-time algorithms that compute WEF allocations with a guaranteed upper bound on total subsidy for monotone valuations and various subclasses thereof. We also present an efficient algorithm to compute a fair allocation of items and money, when the budget is not enough to make the allocation WEF. This algorithm is new even for the unweighted setting.

cs.GT

Weighted Envy Freeness With Bounded Subsidies

We explore solutions for fairly allocating indivisible items among agents assigned weights representing their entitlements. Our fairness goal is weighted-envy-freeness (WEF), where each agent deems their allocated portion relative to their entitlement at least as favorable as any other's relative to their own. In many cases, achieving WEF necessitates monetary transfers, which can be modeled as third-party subsidies. The goal is to attain WEF with bounded subsidies. Previous work in the unweighted setting of subsidies relied on basic characterizations of EF that fail in the weighted settings. This makes our new setting challenging and theoretically intriguing. We present polynomial-time algorithms that compute WEF-able allocations with an upper bound on the subsidy per agent in three distinct additive valuation scenarios: (1) general, (2) identical, and (3) binary. When all weights are equal, our bounds reduce to the bounds derived in the literature for the unweighted setting.

cs.GT

Opinion Diffusion and Campaigning on Society Graphs

We study the effects of campaigning, where the society is partitioned into voter clusters and a diffusion process propagates opinions in a network connecting the clusters. Our model is very powerful and can incorporate many campaigning actions, various partitions of the society into clusters, and very general diffusion processes. Perhaps surprisingly, we show that computing the cheapest campaign for rigging a given election can usually be done efficiently, even with arbitrarily-many voters. Moreover, we report on certain computational simulations.

cs.MA

Strongly Budget Balanced Auctions for Multi-Sided Markets

In two-sided markets, Myerson and Satterthwaite's impossibility theorem states that one can not maximize the gain-from-trade while also satisfying truthfulness, individual-rationality and no deficit. Attempts have been made to circumvent Myerson and Satterthwaite's result by attaining approximately-maximum gain-from-trade: the double-sided auctions of McAfee (1992) is truthful and has no deficit, and the one by Segal-Halevi et al. (2016) additionally has no surplus --- it is strongly-budget-balanced. They consider two categories of agents --- buyers and sellers, where each trade set is composed of a single buyer and a single seller. The practical complexity of applications such as supply chain require one to look beyond two-sided markets. Common requirements are for: buyers trading with multiple sellers of different or identical items, buyers trading with sellers through transporters and mediators, and sellers trading with multiple buyers. We attempt to address these settings. We generalize Segal-Halevi et al. (2016)'s strongly-budget-balanced double-sided auction setting to a multilateral market where each trade set is composed of any number of agent categories. Our generalization refines the notion of competition in multi-sided auctions by introducing the concepts of external competition and trade reduction. We also show an obviously-truthful implementation of our auction using multiple ascending prices.

cs.GT

Double-Sided Markets with Strategic Multi-dimensional Players

We consider mechanisms for markets that are double-sided and have players with multi-dimensional strategic spaces on at least one side. The players of the market are strategic, and act to optimize their own utilities. The mechanism designer, on the other hand, aims to optimize a social goal, i.e., the gain from trade. We focus on one example of this setting which is motivated by the foreseeable future form of online advertising. Online advertising currently supports some of the most important Internet services, including: search, social media and user generated content sites. To overcome privacy concerns, it has been suggested to introduce user information markets through information brokers into the online advertising ecosystem. Such markets give users control over which data get shared in the online advertising exchange. We describe a model for the above foreseeable future form of online advertising, and design two mechanisms for the exchange of this model: a deterministic mechanism which is related to the vast literature on mechanism design through trade reduction and allows players with a multi-dimensional strategic space, and a randomized mechanism which can handle a more general version of the model.

cs.GT

Online Truthful Mechanisms for Multi-sided Markets

The study of mechanisms for multi-sided markets has received an increasingly growing attention from the research community, and is motivated by the numerous examples of such markets on the web and in electronic commerce. Many of these examples represent dynamic and uncertain environments, and thus, require, in fact, online mechanisms. Unfortunately, as far as we know, no previously published online mechanism for a multi-sided market (or even for a double-sided market) has managed to (approximately) maximize the gain from trade, while guaranteeing desirable economic properties such as incentivizing truthfulness, voluntary participation and avoiding budget deficit. In this work we present the first online mechanism for a multi-sided market which has the above properties. Our mechanism is designed for a market setting suggested by [Feldman and Gonen (2016)]; which is motivated by the foreseeable future form of online advertising. The online nature of our setting motivated us to define a stronger notion of individual rationality, called "continuous individual rationality", capturing the natural requirement that a player should never lose either by participating in the mechanism or by not leaving prematurely. Satisfying the requirements of continuous individual rationality, together with the other economic properties our mechanism guarantees, requires the mechanism to use a novel pricing scheme where users may be paid ongoing increments during the mechanism's execution up to a pre-known maximum value. As users rarely ever get paid in reality, this pricing scheme is new to mechanism design. Nevertheless, the principle it is based on can be observed in many common real life scenarios such as executive compensation payments and company acquisition deals. We believe both our new dynamic pricing scheme concept and our strengthened notion of individual rationality are of independent interest.

cs.GT

Optimal Solutions for Multi-Unit Combinatorial Auctions: Branch and Bound Heuristics

Finding optimal solutions for multi-unit combinatorial auctions is a hard problem and finding approximations to the optimal solution is also hard. We investigate the use of Branch-and-Bound techniques: they require both a way to bound from above the value of the best allocation and a good criterion to decide which bids are to be tried first. Different methods for efficiently bounding from above the value of the best allocation are considered. Theoretical original results characterize the best approximation ratio and the ordering criterion that provides it. We suggest to use this criterion.

cs.GT

Linear Programming helps solving large multi-unit combinatorial auctions

Previous works suggested the use of Branch and Bound techniques for finding the optimal allocation in (multi-unit) combinatorial auctions. They remarked that Linear Programming could provide a good upper-bound to the optimal allocation, but they went on using lighter and less tight upper-bound heuristics, on the ground that LP was too time-consuming to be used repetitively to solve large combinatorial auctions. We present the results of extensive experiments solving large (multi-unit) combinatorial auctions generated according to distributions proposed by different researchers. Our surprising conclusion is that Linear Programming is worth using. Investing almost all of one's computing time in using LP to bound from above the value of the optimal solution in order to prune aggressively pays off. We present a way to save on the number of calls to the LP routine and experimental results comparing different heuristics for choosing the bid to be considered next. Those results show that the ordering based on the square root of the size of the bids that was shown to be theoretically optimal in a previous paper by the authors performs surprisingly better than others in practice. Choosing to deal first with the bid with largest coefficient (typically 1) in the optimal solution of the relaxed LP problem, is also a good choice. The gap between the lower bound provided by greedy heuristics and the upper bound provided by LP is typically small and pruning is therefore extensive. For most distributions, auctions of a few hundred goods among a few thousand bids can be solved in practice. All experiments were run on a PC under Matlab.

cs.GT