IJCAI 2026 Papers

Traditional multi-view learning models are primarily designed for static datasets with fixed views. However, in dynamic incremental view environments, this approach inevitably leads to view forgetting, where the introduction of new views weakens previously acquired knowledge. In contrast, the human brain exhibits remarkable memory retention and knowledge transfer capabilities when receiving objects described from different perspectives, with past experience further supplementing new insights. Inspired by underlying neural processing mechanisms, we propose a novel view incremental learning framework named Hebbian View Orthogonal Projection (HVOP). HVOP constructs a knowledge transfer space, where gradient updates are projected onto the orthogonal complement of historical representations, thereby mitigating interference between old and new views. By further incorporating recursive lateral connections and Hebbian learning rules, the proposed model imparts brain-like dynamic adaptability to the learning process, enhancing knowledge transfer and integration, thereby enabling stable knowledge transfer under evolving views. We validate HVOP on node classification tasks, demonstrating its superior performance in both knowledge retention and transfer compared to traditional methods. The results highlight the efficacy of biologically inspired mechanisms in mitigating the view forgetting phenomenon.

Large EEG Models (LEMs) are drawing increasing attention in EEG, as large-scale pretraining yields transferable representations that improve generalization. As EEG research moves to real-world deployment, objectives and paradigms diversify, yielding increasingly heterogeneous and unevenly scaled datasets across institutions. This evolution induces distribution drift and scale imbalance, making static pretrained LEMs brittle and requiring adaptation to newly collected data. Under the constraints of the high cost of retraining and the privacy sensitivity of newly collected data, federated learning offers a practical route to update LEMs via decentralized parameter updates. Yet standard federated fine-tuning is unstable for pretrained LEMs, suffering backbone drift, misaligned updates under non-IID heterogeneity, and scale imbalance. We propose FedGLoRA: we freeze the backbone and communicate only LoRA adapters via a dual-branch design, with a shared global branch and a private on-device branch. FedGLoRA aggregates global updates on a Grassmann subspace with a Grassmann-proximal constraint, and uses bidirectional distillation to mitigate imbalance. Experiments on motor imagery and emotion recognition show consistent gains and improved stability over strong baselines.

Federated learning (FL) has emerged as a distributed machine learning paradigm due to its privacy-preserving advantages. Most FL studies assume offline labeled datasets are available at clients. In practice, however, client data often arrive without labels in a streaming manner, making label acquisition a crucial problem. Existing solutions typically rely on human experts or artificial intelligence (AI) models for annotation. Nevertheless, due to the subjectivity among human experts and the inherent limitations of AI models, the labels they provide are often unreliable. In this work, we propose CoFL, a novel consensus driven human-AI collaborative FL method, which utilizes the complementarity between humans and AI models to produce more reliable labels. Moreover, CoFL leverages cross-client consensus among human experts to further enhance the collaboration process. Experiments on three datasets demonstrate that CoFL consistently outperforms baseline methods under various settings. The code is available at https://github.com/huaiguang233/CoFL.

The diffusion auction is an emerging auction model which leverages social networks to recruit more buyers, thereby improving auction revenue and allocation efficiency. Previous studies on diffusion auctions have primarily focused on the single-parameter domain, where each buyer's valuation function is represented by a single private value. However, due to the complex interdependencies between allocations and network structures, few studies have examined the combinatorial auction domain, in which buyers' valuation functions exhibit multidimensionality. In this paper, we fully characterize implementable diffusion mechanisms within the combinatorial auction domain for the first time. Based on the characterization, we identify a class of allocation policies for each of which the optimal payment, namely the one maximizing the seller's revenue, can be derived in closed form. Furthermore, we apply the established theory to design a practical diffusion combinatorial auction, named the Exhausted-Reference Pricing Mechanism, which is incentive-compatible, individually rational, and weakly budget balanced.

Social Law Synthesis (SLS) in strategic environments is a novel multi-unit mechanism design problem, spanning modeling to computational challenges. We derive a method to specify the problem succinctly, reduce payment determination to allocation determination, and design an integer linear programming (ILP)-based algorithm that further reduces allocation to a polynomial-time ILP formulation. This offloads intractability to powerful ILP solvers, yielding a truthful, individually rational, and profit-optimal mechanism.

We study proportional representation in the temporal voting model, where collective decisions are made repeatedly over time over a fixed horizon. Prior work has extensively investigated how proportional representation axioms from multiwinner voting (e.g., justified representation (JR) and its variants) can be adapted, satisfied, and verified in this setting. However, much less is understood about their interaction with social welfare. In this work, we quantify the efficiency cost of enforcing proportionality. We formalize the welfare-proportionality tension via the worst-case ratio between the maximum achievable utilitarian welfare and the maximum welfare attainable subject to a proportionality axiom. We show that imposing proportional representation in the temporal setting can incur a growing, yet sublinear, welfare loss as the number of voters or rounds increases. We further identify a clean separation among axioms: for JR, the welfare loss diminishes as the time horizon grows and vanishes asymptotically, whereas for stronger axioms this conflict persists even with many rounds. Moreover, we prove that welfare maximization under each axiom is NP-complete and APX-hard, even under static preferences and bounded-degree approvals, and provide fixed-parameter algorithms under several natural structural parameters.

In this paper, we prove the existence of an envy-free up to one item (EF1) division for a discrete chore. Our approach builds upon the powerful Simmons-Su framework, which leverages Sperner’s lemma to guarantee the existence of a simplex corresponding to a sequence of similar fractional divisions, ensuring that each agent is satisfied with a different bundle. For allocations of goods, existing works have introduced rounding techniques that convert an envy-free fractional division into a connected integral EF1 division for any number of agents with monotone valuations. However, the analogous problem for chores has remained unresolved, and existing rounding techniques fail due to the asymmetric definitions of EF1 for goods and chores. To overcome this asymmetry, we refine the existing rounding techniques and show that connected EF1 divisions exist for a discrete chore.

The quantal response (QR) model is widely used in Stackelberg security games (SSGs) to capture boundedly rational adversaries. Existing work on SSGs under QR, however, almost exclusively assumes a homogeneous attacker population, ignoring heterogeneity in attacker preferences and rationality. We study SSG with mixed quantal response attackers, where the follower population consists of multiple discrete attacker types, each following a type-specific QR model. The defender allocates limited resources across targets, while an attacker drawn from this heterogeneous population observes the defender’s strategy and attacks a single target. This results in a highly non-convex equilibrium computation problem. We develop a polynomial-time approximation scheme (PTAS) for this setting when the number of attacker types is bounded, based on an exponential cone programming formulation combined with a carefully designed Branch-and-Bound procedure. Experiments demonstrate that our approach outperforms standard gradient-based methods and that explicitly modeling attacker heterogeneity yields significant gains over traditional SSG models with a single QR attacker.

We address the problem of selecting k representative nodes from a network, aiming to simultaneously achieve two objectives: identifying the most influential nodes and ensuring that the selection proportionally reflects the diversity within the network. We propose a general approach to accomplish this by combining ideas from network science and computational social choice. Notably, our algorithms depend only on the connections between nodes and do not utilize any additional information that would explicitly identify groups of nodes. We analyze them theoretically, and demonstrate their effectiveness through a series of experiments.

Our work evolves around Fictitious Play, one of the first iterative methods that is known to converge to a Nash equilibrium in zero-sum games. In recent years, there has been a revived interest, due to applications in various machine learning problems, which has motivated a line of work on its convergence properties and on proposing new variants of the initial algorithm. Our paper is along this direction and introduces one new variant, which we refer to as Almost Greedy Fictitious Play. The proposed algorithm greedily attempts to find the optimal stepsize at each iteration but its search space is constrained and includes almost all the line between the cumulative mixed strategy and the current best response. Our main result is that the method achieves an instance dependent convergence rate of O(1/T) with respect to the duality gap. This matches the rate of Continuous Fictitious Play, and offers an alternative to discretization. We complement our theoretical findings with experiments that demonstrate the effectiveness of the method.

The Tournament Fixing Problem (TFP) asks whether a knockout tournament can be scheduled to guarantee that a given player v* wins. Although TFP is NP-hard in general, it is known to be fixed-parameter tractable (FPT) when parameterized by the feedback arc/vertex set number, or the in/out-degree of v*. However, it remained open whether TFP is FPT with respect to the subset FAS number of v* --- the minimum number of arcs intersecting all cycles containing v* --- a parameter that is never larger than the aforementioned ones. In this paper, we resolve this question negatively by proving that TFP stays NP-hard even when the subset FAS number of v* is constant ≥ 1 and either the subgraph induced by the in-neighbors D[N_{in}(v*)] or the out-neighbors D[N_{out}(v*)] is acyclic. Conversely, when both D[N_{in}(v*)] and D[N_{out}(v*)] are acyclic, we show that TFP becomes FPT parameterized by the subset FAS number of v*. Furthermore, we provide sufficient conditions under which v* can win even when this parameter is unbounded.

Deterministic auctions are attractive in practice due to their transparency, simplicity, and ease of implementation, motivating a sharper understanding of when they can attain the same outcomes as randomized mechanisms. We study deterministic implementation in single-item auctions under two notions of outcomes: (revenue, welfare) pairs and interim allocations. For (revenue, welfare) pairs, we show a separation in discrete settings: there exists a pair implementable by a deterministic Bayesian incentive-compatible (BIC) auction but not by any deterministic dominant-strategy incentive-compatible (DSIC) auction. For continuous atomless priors, we identify conditions under which deterministic DSIC auctions are equivalent to randomized BIC auctions in terms of achievable outcomes. For interim allocations, under a strict monotonicity condition, we establish a deterministic analogue of Border's theorem for two bidders, providing a necessary and sufficient condition for deterministic DSIC implementability. Using this characterization, we exhibit an interim allocation implementable by a randomized BIC auction but not by any deterministic DSIC auction.

Envy-free (EF) allocation is a fundamental problem at the intersection of theoretical computer science and economics. When resources are indivisible, achieving an EF allocation is often impossible. A common remedy is to compensate agents with subsidies. Brustle et al. proved that a total subsidy of n-1 is both necessary and sufficient to guarantee EF in the worst case, where n is the number of agents and each agent has additive valuations with marginal values of at most 1 per item. In this paper, we consider a constrained setting, namely graph orientation, that was recently introduced by Christodoulou et al. In this model, agents correspond to vertices in a multigraph, and resources correspond to edges, with each edge allocated to one of its two incident agents. Despite extensive study of the graph orientation model, it remains unclear how much subsidy is sufficient to guarantee EF. We show that a total subsidy of n/2 is always sufficient to guarantee EF in any multigraph, halving the subsidy required in the unconstrained setting, and provide a polynomial-time algorithm to compute such an allocation. We show that this bound is tight, even for simple graphs.

We initiate the study of online contracts, which integrate the game-theoretic considerations of economic contract theory, with the algorithmic and informational challenges of online algorithm design. Our starting point is the classic online setting with preemption, in which a hiring principal faces a sequence of adversarial agent arrivals. Upon arrival, the principal must decide whether to tentatively accept the agent to their team, and whether to dismiss previous tentative choices. Dismissal is irrevocable, giving the setting its online decision-making flavor. In our setting, the agents are rational players: once the team is finalized, a game is played where the principal offers contracts (performance-based payment schemes), and each agent decides whether or not to work. Working agents reward the principal, and the goal is to choose a team that maximizes the principal's utility. Our main positive result is a 1/2-competitive algorithm when agent rewards are additive, which matches the best-possible competitive ratio. Our algorithm is randomized and this is necessary, as we show that no deterministic algorithm can attain a bounded competitive ratio. Moreover, if agent rewards are allowed to exhibit combinatorial structure known as XOS, even randomized algorithms might fail. En route to our competitive algorithm, we develop the technique of balance points, which can be useful for further exploration of online contracts in the adversarial model.

We consider the problem of assessing a group of nodes in a network. Our focus is on vitality indices—a natural class of centrality measures that evaluate the importance of a node by examining the impact of its removal on the network. We conduct a comprehensive analysis of group vitality indices. Specifically, we show that every vitality index admits a unique extension to groups, which can be defined using a group variant of the Shapley value recently proposed in the literature. We also provide an axiomatization of the entire class, along with two specific group vitality indices that satisfy additional normalization conditions. Furthermore, we study the computational properties of all vitality indices, as well as Group Attachment Centrality.

Subgame solving is a technique for scaling algorithms to large games by locally refining a precomputed blueprint strategy during gameplay. While straightforward in perfect-information games where search starts from the current state, subgame solving in imperfect-information games must account for hidden states and uncertainty about the opponent's past strategy. Gadget games were developed to ensure that the improved subgame strategy is robust against any possible opponent's strategy in a zero-sum game. Gadget games typically contain infinitely many Nash equilibria. We demonstrate that while these equilibria are equivalent in the gadget game, they yield vastly different performance in the full game, even when facing a rational opponent. We propose gadget game sequential equilibria as the preferred solution concept. We introduce modifications to the sequence-form linear program and counterfactual regret minimization that converge to these refined solutions with only mild additional computational cost. Additionally, we provide several new insights into the surprising superiority of the resolving gadget game over the max-margin gadget game. Our experiments compare different Nash equilibria of gadget games in several standard benchmark games, showing that our refined equilibria consistently outperform unrefined Nash equilibria, and can reduce the exploitability of the overall strategy by more than 50%.

We study the question of existence and fast computation of fair and efficient allocations of indivisible resources among agents with additive valuations. As such allocations may not exist for arbitrary instances, we ask if they exist for typical or random instances, meaning when the utility values of agents for the resources are drawn from certain distributions. In this paper, we extend the previously studied formal models of this problem to non-identical items. We assume that every item is associated with a distribution U_j, and every agent's utility value for the item is drawn independently from U_j. We show that envy-free fair and maximum social welfare efficient allocations exist with high probability in the asymptotic setting, meaning when the number of agents n and items m are large. Further, we show that when m = Ω(n log n), then by only sampling O(log m) or O((log m)^2) utility values per item instead of all the n, we can compute these allocations in Õ(m) time. Finally, we simulate our algorithms on randomly generated instances and show that even for small instances, we suffer small multiplicative losses in the fairness and efficiency guarantees and converge to fully optimal guarantees quickly.

We study the optimal design of a self-financing event, a problem that requires balancing the recruitment of costly, positive-value participants with revenue-generating agents who may impose negative values on the event. We introduce a novel two-sided mechanism design framework with plus agents equipped with private costs and positive impact, and minus agents with private values and negative impact upon inclusion in the event, to maximize the overall quality of the event under a budget-balanced (BB) constraint so that the designer does not run a deficit. We conduct a comprehensive study on the theory of optimal event curation on various utility functions. For additive utility, we fully characterize the optimal incentive-compatible Bayesian mechanism under both the ex-ante and ex-post BB constraints. For submodular utility, we propose an ex-ante BB mechanism that achieves a constant-factor approximation to the optimal Bayesian mechanism.

We study the allocation of m indivisible chores among n agents with additive disutilities under the fairness notion of envy-freeness up to one chore (EF1) and the efficiency notion of Pareto-optimality (PO). Although the existence of an allocation satisfying both EF1 and PO was recently established using a highly non-constructive fixed-point argument, an effective algorithm for computing such an allocation remains elusive, prompting the study of meaningful relaxations of these desiderata. Prior work introduced a natural relaxation through the concept of epistemic fairness: an allocation is said to be epistemic EF1 (EEF1), if for every agent i, it is possible to re-allocate the bundles of agents other than i such that i becomes EF1. In this work, we present a pseudo-polynomial time algorithm for computing an allocation of chores that is both EEF1 and PO. This gives an efficient polynomial-time algorithm for most practical settings where disutility values are integral and polynomially bounded in m and n. Our result employs the competitive equilibrium framework and relies on several technical insights that both utilize the distinct structure of epistemic EF1 and address the challenges it introduces.