容迟网络中基于演化博弈的合作行为

针对容迟网络中节点由于资源有限而表现出来的自私特性,为改善网络中节点的合作行为,进而提高网络的整体性能,提出一种基于演化博弈(EGT)的节点合作行为促进机制。首先,采用囚徒困境模型建立节点与其邻居博弈的收益矩阵;其次,基于度中心性定义节点的社会权威性;进一步地,在节点策略更新规则时考虑社会权威的影响,选择当前邻居中社会权威较高的节点进行模仿学习;最后,在机会网络环境仿真器上基于真实的动态网络拓扑数据进行仿真实验。仿真结果表明,与随机选择邻居的费米(Fermi)更新规则相比,考虑社会权威的更新规则能够更好地促进节点合作行为的涌现,进而提升网络的整体性能。     

惩罚因子在重复囚徒困境博弈中的研究

针对囚徒困境博弈中收益矩阵参数无法动态更新的问题,提出一个带惩罚因子的囚徒困境博弈模型。该模型中的个体可以根据自身的策略,动态修改收益矩阵中的参数,在每轮博弈之后个体根据邻居收益更新自己的策略。仿真结果表明,惩罚因子可以有效地促进合作策略的涌现,另外发现,合作策略的涌现不仅与惩罚因子有关,而且与网络个体的初始策略有关。当社团内部的个体采取相同策略,社团之间采取不同策略时,更有利于合作策略的涌现。最后,惩罚因子还可以提高参与者的平均收益。     

共演化博弈中的反馈机制

本文研究共演化动力学在合作演化中的作用.系统的状态由个体的策略决定.系统状态与个体的属性共同演化,形成一种反馈机制.特别是当个体能够根据博弈的结果调整社会关系时,这种调整势必影响未来的博弈.这种反馈机制在适当的时间尺度下,总是能够促进合作.首先,分析了个体策略与群组属性共演化的情形,在基于个体选择的层面上,结合溯祖理论和演化集合论,给出了区域性利他行为涌现的条件.其次,给出了结构群体中策略选择的参数判据,将两策略判据和适应动力学结合起来,发现通过调整与收益矩阵无关的参数可以实现性能控制.最后,研究了不同的角色分配方案在最后通牒博弈中对公平行为演化的影响,发现当个体的先行者优势或所配置的资源依赖于先前分配结果时,公平的分配方案及对公平的要求得以建立.共演化这种反馈机制在用博弈论解决编队控制、资源配置方案设计等实际问题时显示出广泛的应用前景.     

基于演化博弈研究移动和噪声对合作的影响

针对规则格子上的节点的自私行为不能有效抑制的问题,提出一个结合个体移动和噪声因素的演化囚徒困境模型。该模型结合ALLC、ALLD、TFT和TF2T四种策略来分析个体移动和噪声两个因素分别和共同对演化博弈中合作行为的影响。模型中的博弈者根据收益差异,可以移动到比当前位置收益高的邻居域的空位置,并且在反复博弈过程学习、模仿,不断调整博弈策略,提高博弈所得,最后达到进化稳定状态。最后在Matlab平台上进行仿真实验,实验结果表明,该模型能够促使个体合作,并且对个体的欺骗行为具有抑制作用。     

二维平面网格上移动成本群体合作行为研究

从移动成本、收益期望与空间博弈的角度,探讨多主体系统的博弈策略演化与系统涌现特征之间的关系。利用空间演化博弈理论,构建了基于个体移动机制的拓扑结构时刻演变的空间演化博弈模型,分析了当主体具有不同的移动成本与收益期望时系统演化的稳定策略,通过分析稳定策略深入探讨系统中合作簇涌现的机理。仿真结果表明,提高移动成本能够最有效地促进系统合作率,同时中等水平的个体收益期望会进一步促进高移动成本的影响效果。     

基于囚徒困境策略的改进HK网络上的合作博弈

为模拟现实世界的合作行为,本文在HK网络模型基础上提出了一种具有高聚类幂律可调性质的新的网络模型,并分析了囚徒困境博弈在此网络上的演化。通过仿真实验,研究了该网络的高聚类特性对合作行为的影响。大量实验表明,网络的高聚类特性可以极大促进合作现象的涌现。同时研究也发现,随着诱惑参数的变大,合作水平也会随之下降,但幅度不大。总之,该演化博弈模型可以促进合作现象的涌现并抵御背叛策略的传播。     

基于利他激励的群体演化合作模型

为探究个体与系统状态的演化,构建了个体行为策略与网络结构的演化模型,探讨个体在利他激励机制下对合作演化的影响。在该模型中,个体首先通过对其他个体的帮助获得一定的额外互惠收益,并通过个体混合收益累计个体收益与帮助其他个体获得额外收益的加权,以此来激励个体合作。然后在博弈过程中,通过个体混合收益取代费米函数中的个体累计收益用于促进个体选择利他合作策略,从而促进整个群体的总收益与合作水平。蒙特卡罗仿真实验结果表明,个体在利他激励机制下更愿意帮助其他个体。在不同网络结构中,小世界网络最能扩散利他激励机制,其系统合作者密度最高。     

一种改进的企业竞争合作进化博弈模型

结合企业决策风格,提出一种引入企业声誉的竞争合作进化博弈模型。该模型以企业声誉传播半径为基础定义邻居企业,从邻居企业中选择博弈对象企业,根据其决策风格产生连续博弈序列,得到博弈收益和企业声誉,并通过计算企业吸引值选择学习对象企业。实验结果表明,该模型可有效区分不同声誉的企业,并使具有良好声誉的企业表现出较强的生存优势以及较高的存活率。     

NIPD博弈的策略结构分析

多人重复囚徒博弈(NIPD)模型经常被用于社会、经济、生物等复杂系统中合作进化问题的研究.针对传统策略方案在研究大N值情况下合作演化时的不足,结合现实中的博弈模式提出个体策略的分级编码方案,并从悖论假设和策略结构两个方面分析了NIPD在高N值时不能涌现大规模合作的原因.仿真实验表明,基于分级编码的NIPD模型具有更小的策略空间和更高的系统合作率,新方案适合于任何N值的NIPD研究,同时策略级数的大小对于合作涌现十分重要.     

理性背叛的推荐合作激励机制

为了促进协作系统中用户的合作行为,激励机制得到了广泛的使用.然而,现有的激励机制往往存在无条件合作策略占优互惠策略的现象,进而抑制了合作的涌现.为了解决这一问题,本文在推荐激励模型上进一步考虑了用户的理性背叛行为.以演化博弈为框架,研究了理性背叛机制在全局平均学习和当前最优学习两种模式下的策略演化特性.结合实际场景,本文还研究了在非完美推荐下理性背叛机制的鲁棒性问题,并且基于余弦相似度提出了一种策略识别方案.最后,通过大量的数值实验与仿真实验,验证了理性背叛机制的理论特性,也展示了该机制在促进合作方面的有效性能.     

An Eigentrust dynamic evolutionary model in P2P file-sharing systems

Many reputation systems have been proposed to distinguish malicious peers and to ensure the quality of the service in P2P file sharing systems. Most of those reputation systems implicitly assumed that normal peers are always altruistic and provide their resources unconditionally when requested. However, as independent decision makers in real networks, peers can be completely altruistic (always cooperative, ALLC), purely selfish (always defective, ALLD), or reciprocal (R). In addition, those systems do not provide an effective method to reduce free-riders in P2P networks. To address these two problems, in this paper, we propose an EigenTrust evolutionary game model based on the renowned EigenTrust reputation model. In our model, we use evolutionary game theory to model strategic peers and their transaction behaviors, which is close to the realistic scenario. Many experiments have been designed and performed to study the evolution of strategies and the emergence of cooperation under our proposed EigenTrust evolutionary model. The simulation results showed that rational users are inclined to cooperate (enthusiastically provide resources to other peers) even under some conditions in which malicious peers try to destroy the system.     

The Impact of Payoff Function and Local Interaction on the N-Player Iterated Prisoner's Dilemma

The N-player iterated prisoner's dilemma (NIPD) game has been widely used to study the evolution of cooperation in social, economic and biological systems. This paper studies the impact of different payoff functions and local interactions on the NIPD game. The evolutionary approach is used to evolve game-playing strategies starting from a population of random strategies. The different payoff functions used in our study describe different behaviors of cooperation and defection among a group of players. Local interaction introduces neighborhoods into the NIPD game. A player does not play against every other player in a group any more. He only interacts with his neighbors. We investigate the impact of neighborhood size on the evolution of cooperation in the NIPD game and the generalization ability of evolved strategies. Received 18 August 1999 / Revised 27 February 2000 / Accepted 15 May 2000     

Multi-objective design method based on evolution game and its application for suspension

Through research and bionics of biology survival mode, game players with competition, cooperation and self-adaptation capacity are introduced in the multi-objective design. The dynamic behavior and bounded rationality in game processes for players are considered according to Chinese saying “In success, commit oneself to the welfare of the society; in distress, maintain one’s own integrity”. An evolution rule, Poor-Competition-Rich-Cooperation (short for PCRC), is proposed. Then, the corresponding payoff functions of competition and cooperation behavior are established and a multi-objective design method based on evolution game is proposed. The calculation steps are as follows: 1) Taking the design objectives as different game players, and calculating factors of the design variables to objective and fuzzy clustering. The design variables are divided into multiple strategy subsets owned by each game player. 2) According to the evolution rule, each player determines its behavior and payoff function in this game round. 3) In their own strategy subsets, each game player takes their payoff as mono-objective for optimization. It gives the best strategy upon other players. And so the best strategies of all players conform the group strategy in this round. The final equilibrium solution is obtained through multi-round game based on convergence criterion. The validity and reliability of this method are shown by the results of an example of a tri-objective optimization design of passive suspension parameters.     

A voter model of the spatial prisoner's dilemma

The prisoner's dilemma (PD) involves contests between two players and may naturally be played on a spatial grid using voter model rules. In the model of spatial PD discussed here, the sites of a two-dimensional lattice are occupied by strategies. At each time step, a site is chosen to play a PD game with one of its neighbors. The strategy of the chosen site then invades its neighbor with a probability that is proportional to the payoff from the game. Using results from the analysis of voter models, it is shown that with simple linear strategies, this scenario results in the long-term survival of only one strategy. If three nonlinear strategies have a cyclic dominance relation between one another, then it is possible for relatively cooperative strategies to persist indefinitely. With the voter model dynamics, however, the average level of cooperation decreases with time if mutation of the strategies is included. Spatial effects are not in themselves sufficient to lead to the maintenance of cooperation     

Evolution of cooperation in reputation system by group-based scheme

Reputation systems are very useful in large online communities in which users may frequently have the opportunity to interact with users with whom they have no prior experience. Recently, how to enhance the cooperative behaviors in the reputation system has become to one of the key open issues. Emerging schemes focused on developing efficient reward and punishment mechanisms or capturing the social or economic properties of participants. However, whether this kind of method can work widely or not has been hard to prove until now. Research in evolutionary game theory shows that group selection (or multilevel selection) can favor the cooperative behavior in the finite population. Furthermore, some recent works give fundamental conditions for the evolution of cooperation by group selection. In the paper, we extend the original group selection theory and propose a group-based scheme to enhance cooperation for online reputation systems. Related concepts are defined to capture the social structure and ties among participants in reputation system, e.g., group, assortativity, etc. Also, we use a Fermi distribution function to reflect the bounded rationality of participants and the existence of stochastic factors in evolutionary process. Extended simulations show that our scheme can enhance cooperation and improve the average performance of participants (e.g. payoff) in reputation system.     

Risk consideration and cooperation in the iterated prisoner’s dilemma

This paper investigates the cooperative behavior in the two-player iterated prisoner’s dilemma (IPD) game with the consideration of income stream risk. The standard deviation of one-move payoffs for players is defined for measuring the income stream risk, and thus the risk effect on the cooperation in the two-player IPD game is examined. A two-population coevolutionary learning model, embedded with a niching technique, is developed to search optimal strategies for two players to play the IPD game. As experimental results illustrate, risk-averse players perform better than risk-seeking players in cooperating with opponents. In particular, in the case with short game encounters, in which cooperation has been demonstrated to be difficult to achieve in previous work, a high level of cooperation can be obtained in the IPD if both players are risk-averse. The reason is that risk consideration induces players to negotiate for stable gains, which lead to steady mutual cooperation in the IPD. This cooperative pattern is found to be quite robust against low levels of noise. However, with increasingly higher levels of noise, only intermediate levels of cooperation can be achieved in games between two risk-averse players. Games with risk-seeking players get to even lower cooperation levels. By comparing the players’ strategies coevolved with and without a high level of noise, the main reason for the reduction in the extent of cooperation can be explained as the lack of contrition and forgiveness of players in the high-noise interactions. Moreover, although increasing encounter length is helpful in improving cooperation in the noiseless and low-noise IPD, we find that it may enforce the absence of contrition and forgiveness, and thus make cooperation even more difficult in the high-noise games.     

Effects of strategy switching and network topology on decision-making in multi-agent systems

To study why the altruistic cooperation can emerge and maintain among self-interested individuals, researchers across several disciplines have made contributions for the solutions of this fascinating problem. Among this, a most-often used framework to describe cooperative dilemma is the evolutionary game theory. In traditional settings, an ideal hypothesis that individuals can feasibly obtain related partners' pay-offs for strategy updating is often adopted. However, considering the impracticality in acquiring accurate pay-offs of referential objects at each round of interaction, we propose switching probability which is independent of pay-offs and denotes the willingness of any individual shifts to another strategy. Here we provide results for the evolutionary dynamics driven by the switching probability in a three-strategy game model, played by the fully connected populations. The findings inform the befitting design of switching probabilities which maximally promote cooperation. We also derive general results that characterise the interaction of the three strategies: coexistence of multiple strategies or domination by some strategy.     

Cooperation in the evolutionary iterated prisoner’s dilemma game with risk attitude adaptation

The Iterated Prisoner’s Dilemma (IPD) game has been commonly used to investigate the cooperation among competitors. However, most previous studies on the IPD focused solely on maximizing players’ average payoffs without considering their risk preferences. By introducing the concept of income stream risk into the IPD game, this paper presents a novel evolutionary IPD model with agents seeking to balance between average payoffs and risks with respect to their own risk attitudes. We build a new IPD model of multiple agents, in which agents interact with one another in the pair-wise IPD game while adapting their risk attitudes according to their received payoffs. Agents become more risk averse after their payoffs exceed their aspirations, or become more risk seeking after their payoffs fall short of their aspirations. The aspiration levels of agents are determined based on their historical self-payoff information or the payoff information of the agent population. Simulations are conducted to investigate the emergence of cooperation under these two comparison methods. Results indicate that agents can sustain a highly cooperative equilibrium when they consider only their own historical payoffs as aspirations (called historical comparison) in adjusting their risk attitudes. This holds true even for the IPD with a short game encounter, for which cooperation was previously demonstrated difficult. However, when agents evaluate their payoffs in comparison with the population average payoff (called social comparison), those agents with payoffs below the population average tend to be dissatisfied with the game outcomes. This dissatisfaction will induce more risk-seeking behavior of agents in the IPD game, which will constitute a strong deterrent to the emergence of mutual cooperation in the population.