Strategyproofness in network auctions requires that bidders not only report their valuations truthfully, but also do their best to invite neighbours from the social network. In contrast to canonical auctions, where the value-monotone allocation in Myerson's Lemma is a cornerstone, a general principle of allocation rules for strategyproof network auctions is still missing. We show that, due to the absence of such a principle, even extensions to multi-unit network auctions with single-unit demand present unexpected difficulties, and all pioneering researches fail to be strategyproof. For the first time in this field, we identify two categories of monotone allocation rules on networks: Invitation-Depressed Monotonicity (ID-MON) and Invitation-Promoted Monotonicity (IP-MON). They encompass all existing allocation rules of network auctions as specific instances. For any given ID-MON or IP-MON allocation rule, we characterize the existence and sufficient conditions for the strategyproof payment rules, and show that among all such payment rules, the revenue-maximizing one exists and is computationally feasible. With these results, the obstacle of combinatorial network auction with single-minded bidders is now resolved.

Graph Neural Networks (GNNs) have achieved outstanding performance across a wide range of graph-related tasks. However, their "black-box" nature poses significant challenges to their explainability, and existing methods often fail to effectively capture the intricate interaction patterns among nodes within the network. In this work, we propose a novel explainability framework, GraphEXT, which leverages cooperative game theory and the concept of social externalities. GraphEXT partitions graph nodes into coalitions, decomposing the original graph into independent subgraphs. By integrating graph structure as an externality and incorporating the Shapley value under externalities, GraphEXT quantifies node importance through their marginal contributions to GNN predictions as the nodes transition between coalitions. Unlike traditional Shapley value-based methods that primarily focus on node attributes, our GraphEXT places greater emphasis on the interactions among nodes and the impact of structural changes on GNN predictions. Experimental studies on both synthetic and real-world datasets show that GraphEXT outperforms existing baseline methods in terms of fidelity across diverse GNN architectures , significantly enhancing the explainability of GNN models.

Multimodal handwritten signatures usually involve offline images and online sequences. Since in real-world scenarios, different modalities of the same signature are generated simultaneously, most research hypothesizes that the different modalities are consistent. However, attacks launched on a partial modality (e.g., only tampering on the image modality) of signature data are commonly seen, and will cause the inter-modal inconsistency. In this paper, we propose and analyze the multimodal security and attack levels for handwritten signatures, and provide a multimodal consistency learning method to detect different levels of attacks of signatures. The modalities include not only traditional offline and online data, but also videos capturing hand movements. We collect a number of triple modal signatures to address the scarcity of public handwritten video datasets. Then, we extract hand joint sequences from videos and utilize them to analyze subtle multimodal consistency with the online modality. We provide extensive experiments for the consistency between online and offline signatures, as well as between online signatures and movement videos. The verification involves distance-based and classification-based fusion models, showing the most effective discriminative networks for attack detection and the superiority of consistency learning.

Signed graphs can model friendly or antagonistic relations where edges are annotated with a positive or negative sign. The main downstream task in signed graph analysis is $\textit{link sign prediction}$. Signed Graph Neural Networks (SGNNs) have been widely used for signed graph representation learning. While significant progress has been made in SGNNs research, two issues (i.e., graph sparsity and unbalanced triangles) persist in the current SGNN models. We aim to alleviate these issues through data augmentation ($\textit{DA}$) techniques which have demonstrated effectiveness in improving the performance of graph neural networks. However, most graph augmentation methods are primarily aimed at graph-level and node-level tasks (e.g., graph classification and node classification) and cannot be directly applied to signed graphs due to the lack of side information (e.g., node features and label information) in available real-world signed graph datasets. Random $\textit{DropEdge} $is one of the few $\textit{DA}$ methods that can be directly used for signed graph data augmentation, but its effectiveness is still unknown. In this paper, we first provide the generalization bound for the SGNN model and demonstrate from both experimental and theoretical perspectives that the random $\textit{DropEdge}$ cannot improve the performance of link sign prediction. Therefore, we propose a novel signed graph augmentation method, $\underline{S}$igned $\underline{G}$raph $\underline{A}$ugmentation framework (SGA). Specifically, SGA first integrates a structure augmentation module to detect candidate edges solely based on network information. Furthermore, SGA incorporates a novel strategy to select beneficial candidates. Finally, SGA introduces a novel data augmentation perspective to enhance the training process of SGNNs. Experiment results on six real-world datasets demonstrate that SGA effectively boosts the performance of diverse SGNN models, achieving improvements of up to 32.3\% in F1-micro for SGCN on the Slashdot dataset in the link sign prediction task.

In auction theory, a core is a stable outcome where no subgroup of participants can achieve better results for themselves. Core-competitive auctions aim to generate revenue that is achievable in a core. They are particularly important because they not only generate optimized revenue for the seller, but also provide an efficient and stable environment for participants. We generalize the design of core-competitive auctions to encompass partially observable networked markets (PONM). Unlike traditional auctions, which often deal with scenarios of limited trading activity, our approach to core-competitive auctions for PONM captures the nature of real-world transaction markets, which is a large linking world for the economic entities and commodities circulate among the entities in the market. Our generalizing the auction market to PONM can much improve the liquidity of the auction, and is especially meaningful for the web economics. Specifically, we quantify the upper and lower bounds of the minimum core revenue in PONM, and further prove that there does not exist any truthful auction for PONM which is efficient and core-competitive. Governed by this impossible result, we identify the criteria that the allocation rule for PONM should meet. Based on these criteria, we propose a new class of auction mechanisms for PONM that is individually rational, incentive-compatible, and core-competitive.

We propose a novel protocol for crowdsourcing and crowdsensing by integrating combinatorial auctions and networks. With this protocol, agents who have already participated in crowdsourcing or crowdsensing tasks are incentivized to invite other agents to join the task. This new protocol aims to attract a growing number of skilled agents, thereby significantly improving the performance of crowdsourcing and crowdsensing. The challenge to this objective is how to incentivize each participant not only to contribute her full ability but also to try her best to spread the task information to her neighbors in the network. This problem is called networked auction or diffusion auction, which is a very new topic in algorithmic game theory and AI and has attracted considerable attention in recent years. Notably, current diffusion auctions lack customization for crowdsourcing or crowdsensing scenarios. Furthermore, no established diffusion auction adequately addresses the intricacies of handling multiple or even combinatorial tasks. This work is the first to design networked auction protocols for combinatorial tasks. From both theory and experiments, we have shown that the new protocols are proven to be incentive compatible, and that both the system’s cost and the requester’s costs could be decreased.

In a crowdsourcing contest, a principal holding a task posts it to a crowd. People in the crowd then compete with each other to win the rewards. Although in real life, a crowd is usually networked and people influence each other via social ties, existing crowdsourcing contest theories do not aim to answer how interpersonal relationships influence people’s incentives and behaviors and thereby affect the crowdsourcing performance. In this work, we novelly take people’s social ties as a key factor in the modeling and designing of agents’ incentives in crowdsourcing contests. We establish two contest mechanisms by which the principal can impel the agents to invite their neighbors to contribute to the task. The first mechanism has a symmetric Bayesian Nash equilibrium, and it is very simple for agents to play and easy for the principal to predict the contest performance. The second mechanism has an asymmetric Bayesian Nash equilibrium, and agents’ behaviors in equilibrium show a vast diversity which is strongly related to their social relations. The Bayesian Nash equilibrium analysis of these new mechanisms reveals that, besides agents’ intrinsic abilities, the social relations among them also play a central role in decision-making. Moreover, we design an effective algorithm to automatically compute the Bayesian Nash equilibrium of the invitation crowdsourcing contest and further adapt it to a large graph dataset. Both theoretical and empirical results show that the new invitation crowdsourcing contests can substantially enlarge the number of participants, whereby the principal can obtain significantly better solutions without a large advertisement expenditure.

Poker game has become one of the most prevailing benchmark environment to discover algorithms for sequential games with imperfect information (SGII). However, in games with large state space, it is hard to traverse the whole game tree. This is because the space of history is exponentially increasing with the input size of the game. Other attempts like truncating the game tree with certain length have also been made to solve this problem. But determine the most suitable length could require enormous amount of resources. All of these obstacles make algorithms for SGII much harder to design. To solve this kind of problem, we propose the adaptive memory sampling method which aims to find the distribution of the sampling length by using posterior sampling to update it iteratively. In the real-world human interaction, to what extent a human memory can last often varies significantly depending on the importance of the interaction trajectory. So we also adopted the Long Short-Term Memory (LSTM) network as the sub-procedure to classify the histories and making prediction of future game states and actions based on historical sampled data. According to our theoretical analysis, our method performs better than the state-of-the-art algorithms. On the other hand, The empirical results support our results.

Multi-agent reinforcement learning (MARL) is an abstract framework modeling a dynamic environment that involves multiple learning and decision-making agents, each of which tries to maximize her cumulative reward. In MARL, each agent discovers a strategy alongside others and adapts her policy in response to the behavioural changes of others. A fundamental difficulty faced by MARL is that every agent is dynamically learning and changing to improve her reward, making the whole system unstable and agents’ policies difficult to converge. In this paper, we introduce the entropy regularizer into the Bellman equation and utilize Lagrange approach to optimize the entropy regularizer. We then propose a MARL algorithm based on the maximum entropy principle and the actor-critic method. This algorithm follows the policy gradient approach and uses a policy network and a value network. We call it Multi-Agent Deep Soft Policy Gradient (MADSPG). Then by using the Lagrange approach and dynamic minimax optimization, we propose the AUTO-MADSPG algorithm with an automatically adjusted entropy regularizer. These algorithms make multi-agent learning more stable while sufficient exploration is guaranteed. Finally, we also incorporate MADSPG with the recently proposed opponent modeling component into an integrated framework. This framework outperforms many state-of-the-art MARL algorithms in conventional cooperative and competitive game settings.

In recent years, a new branch of auction models called diffusion auction has extended the traditional auction into social network scenarios. The diffusion auction models the auction as a networked market whose nodes are potential customers and whose edges are the relations between these customers. The diffusion auction mechanism can incentivize buyers to not only submit a truthful bid, but also further invite their surrounding neighbors to participate into the auction. It can convene more participants than traditional auction mechanisms, which leads to better optimizations of different key aspects, such as social welfare, seller’s revenue, amount of redistributed money and so on. The diffusion auctions have recently attracted a discrete interest in the algorithmic game theory and market design communities. This survey summarizes the current progress of diffusion auctions.

In this article, an improved short-term speed prediction method is proposed to predict short-term future speed and analyze future energy consumption of intelligent fuel cell vehicles. The short-term future speed is predicted by the proposed Inflated 3-D Inception long short-term memory (LSTM) network, which takes the spatiotemporal-vision information and vehicle motion states. Specifically, the spatiotemporal-vision-based deep neural network utilizes image sequences captured by a front-facing camera as environmental information and historical speed series as motion information to improve the prediction accuracy. Then, a case study of the proposed speed prediction method, with rule-based energy management strategy to calculate future energy consumption, is presented. The simulation results show that short-term speed prediction based on the Inflated 3-D Inception LSTM network can achieve high accuracy of speed prediction in various traffic densities, as well as low prediction errors of future energy consumption including the hydrogen consumption and state-of-charge attenuation.

Diffusion auction is a new model in auction design. It can incentivize the buyers who have already joined in the auction to further diffuse the sale information to others via social relations, whereby both the seller's revenue and the social welfare can be improved. Diffusion auctions are essentially non-typical multidimensional mechanism design problems and agents' social relations are complicatedly involved with their bids. In such auctions, incentive-compatibility (IC) means it is best for every agent to honestly report her valuation and fully diffuse the sale information to all her neighbors. Existing work identified some specific mechanisms for diffusion auctions, while a general theory characterizing all incentive-compatible diffusion auctions is still missing. In this work, we identify a sufficient and necessary condition for all dominant-strategy incentive-compatible (DSIC) diffusion auctions. We formulate the monotonic allocation policies in such multidimensional problems and show that any monotonic allocation policy can be implemented in a DSIC diffusion auction mechanism. Moreover, given any monotonic allocation policy, we obtain the optimal payment policy to maximize the seller's revenue.

Enforcing cooperation among substantial agents is one of the main objectives for multi-agent systems. However, due to the existence of inherent social dilemmas in many scenarios, the free-rider problem may arise during agents’ long-run interactions and things become even severer when self-interested agents work in collusion with each other to get extra benefits. It is commonly accepted that in such social dilemmas, there exists no simple strategy for an agent whereby she can simultaneously manipulate on the utility of each of her opponents and further promote mutual cooperation among all agents. Here, we show that such strategies do exist. Under the conventional repeated public goods game, we novelly identify them and find that, when confronted with such strategies, a single opponent can maximize his utility only via global cooperation and any colluding alliance cannot get the upper hand. Since a full cooperation is individually optimal for any single opponent, a stable cooperation among all players can be achieved. Moreover, we experimentally show that these strategies can still promote cooperation even when the opponents are both self-learning and collusive.

Auction is the common paradigm for resource allocation which is a fundamental problem in human society. Existing research indicates that the two primary objectives, the seller's revenue and the allocation efficiency, are generally conflicting in auction design. For the first time, we expand the domain of the classic auction to a social graph and formally identify a new class of auction mechanisms on graphs. All mechanisms in this class are incentive-compatible and also promote all buyers to diffuse the auction information to others, whereby both the seller's revenue and the allocation efficiency are significantly improved comparing with the Vickrey auction. It is found that the recently proposed information diffusion mechanism is an extreme case with the lowest revenue in this new class. Our work could potentially inspire a new perspective for the efficient and optimal auction design and could be applied into the prevalent online social and economic networks.

Repeated game has long been the touchstone model for agents’ long-run relationships. Previous results suggest that it is particularly difficult for a repeated game player to exert an autocratic control on the payoffs since they are jointly determined by all participants. This work discovers that the scale of a player’s capability to unilaterally influence the payoffs may have been much underestimated. Under the conventional iterated prisoner’s dilemma, we develop a general framework for controlling the feasible region where the players’ payoff pairs lie. A control strategy player is able to confine the payoff pairs in her objective region, as long as this region has feasible linear boundaries. With this framework, many well-known existing strategies can be categorized and various new strategies with nice properties can be further identified. We show that the control strategies perform well either in a tournament or against a human-like opponent.

In an economic market, sellers, infomediaries and customers constitute an economic network. Each seller has her own customer group and the seller's private customers are unobservable to other sellers. Therefore, a seller can only sell commodities among her own customers unless other sellers or infomediaries share her sale information to their customer groups. However, a seller is not incentivized to share others' sale information by default, which leads to inefficient resource allocation and limited revenue for the sale. To tackle this problem, we develop a novel mechanism called customer sharing mechanism (CSM) which incentivizes all sellers to share each other's sale information to their private customer groups. Furthermore, CSM also incentivizes all customers to truthfully participate in the sale. In the end, CSM not only allocates the commodities efficiently but also optimizes the seller's revenue.

This paper studies an auction design problem for a seller to sell a commodity in a social network, where each individual (the seller or a buyer) can only communicate with her neighbors. The challenge to the seller is to design a mechanism to incentivize the buyers, who are aware of the auction, to further propagate the information to their neighbors so that more buyers will participate in the auction and hence, the seller will be able to make a higher revenue. We propose a novel auction mechanism, called information diffusion mechanism (IDM), which incentivizes the buyers to not only truthfully report their valuations on the commodity to the seller, but also further propagate the auction information to all their neighbors. In comparison, the direct extension of the well-known Vickrey-Clarke-Groves (VCG) mechanism in social networks can also incentivize the information diffusion, but it will decrease the seller's revenue or even lead to a deficit sometimes. The formalization of the problem has not yet been addressed in the literature of mechanism design and our solution is very significant in the presence of large-scale online social networks.

In cognitive radio networks, primary user emulation (PUE) attack is a denial-of-service (DoS) attack on secondary users. It means that a malicious attacker sends primary-user-like signals to jam certain spectrum channels during the spectrum sensing period. Sensing the attacker's signal, the legitimate secondary user will regard these channels are used by the primary users, and give up using these attacked channels. In this paper, the interaction between the PUE attacker and the secondary user is modeled as a constant sum differential game which is called PUE attak game. The secondary user's objective is to find the optimal sensing strategy so as to maximize its overall channel usability, while the attacker's objective is to minimize the secondary user's overall channel usability. The Nash equilibrium solution of this PUE attack game is deprived, and the optimal anti-PUE attack strategy is obtained. Numerical results demonstrate the trajectories of the secondary user's optimal channel sensing strategies over time, and also shows that: by following the differential game solution, the secondary user can always optimize its channel usability when confronting PUE attacks.

In cognitive radio networks, one key feature of spectrum trading is its short term or, even, real time, since the spectrum availability, quality, and price keep changing over time. Therefore, a spectrum pricing policy should be dynamically optimal. In this work, we address the real-time optimal pricing problem for primary users. Based on differential game model, we analyze the optimal pricing strategy for QoS-aware dynamic networks in which the secondary users' number and primary users' QoS level keep changing over time. Nash equilibrium is derived and an optimal pricing and QoS setting policy is formulated. Since the Nash equilibrium of our differential game based model deals with optimal pricing in each time instance, the real-time optimal pricing characteristic can be realized.

Sybil Attack means one node counterfeits multiple identities. It poses great threats to the routing of wireless ad hoc networks. Many existing solutions employ local detection method to capture misbehavior and then enhance the detection accuracy by information exchange. However, they ignore the rationality of member nodes. To save resource, rational nodes are reluctant to share information, therefore, how to guarantee reliable information exchange becomes a challenge issue. This paper presents a cooperative detection method against Sybil attack. Our method adopts the reputation mechanism which relies on the observation exchange to differentiate Sybil identities from legitimate ones. To promote the observation exchange, we present a cooperative detection game with initial condition, which helps nodes be aware that with which to share the observations can bring the maximum utilities. The theoretical and numerical analysis indicate that only benign and unselfish nodes can be accepted by their rational neighbors while Sybil nodes are excluded from the information exchange.