The iterated prisoner's dilemma(IPD) is an ideal model for analyzing interactions between agents in complex networks. It has attracted wide interest in the development of novel strategies since the success of tit-...The iterated prisoner's dilemma(IPD) is an ideal model for analyzing interactions between agents in complex networks. It has attracted wide interest in the development of novel strategies since the success of tit-for-tat in Axelrod's tournament. This paper studies a new adaptive strategy of IPD in different complex networks, where agents can learn and adapt their strategies through reinforcement learning method. A temporal difference learning method is applied for designing the adaptive strategy to optimize the decision making process of the agents. Previous studies indicated that mutual cooperation is hard to emerge in the IPD. Therefore, three examples which based on square lattice network and scale-free network are provided to show two features of the adaptive strategy. First, the mutual cooperation can be achieved by the group with adaptive agents under scale-free network, and once evolution has converged mutual cooperation, it is unlikely to shift. Secondly, the adaptive strategy can earn a better payoff compared with other strategies in the square network. The analytical properties are discussed for verifying evolutionary stability of the adaptive strategy.展开更多
Introduction: Hepatitis B virus (HBV) infection is a major public health problem in Cameroon. Garoua city is the headquarters of the North Region of Cameroon, where the HBV prevalence is among the highest of the count...Introduction: Hepatitis B virus (HBV) infection is a major public health problem in Cameroon. Garoua city is the headquarters of the North Region of Cameroon, where the HBV prevalence is among the highest of the country. The aim of this study was to determine the prevalence of HBsAg carriage and associated factors among persons incarcerated in the Garoua Central Prison. Methods: It was a cross-sectional study conducted from July 1 to July 31, 2023 at the Garoua Central prison. We included all prisoners willing to participate in the study and who gave their verbal consent. We collected data using a pre-established data entry form and we used rapid test for blood screening for HBV surface antigen (HBs Ag) with ELISA confirmation. Data were analyzed using the R<sup>®</sup> software for Windows. After the univariate analysis, we selected associated variables to HBV infection with p-value p-value was set at 5%. Results: We included 1389 prisoners out of which 97.6% were male. The median age (IQR) of the study population was 28 (23 - 35) years. The median (IQR) duration of incarceration was 12 (6 - 26) months and the mean (±sd) number of incarcerations was 1.24 (±0.6). HBV prevalence was estimated at 14.8% (95% CI: 13.0 - 16.7). Upon uni- and multivariate analysis, no risk factor was significantly associated with viral hepatitis B infection in our study population. Conclusion: The prevalence of Hepatitis B was high in the Garoua Central Prison, but there were no additional risk factors for HBV infection. There is a need to include the Garoua Central Prison and by the way other prisons in the country in the chronic viral hepatitis care program.展开更多
BACKGROUND Prisons can be a reservoir for infectious diseases,including severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),due to the very intimate nature of the living spaces and the large number of people f...BACKGROUND Prisons can be a reservoir for infectious diseases,including severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),due to the very intimate nature of the living spaces and the large number of people forced to share them.AIM To investigate the SARS-CoV-2 epidemiology in prisons,this study evaluated the infection incidence rate in prisoners who underwent nasopharyngeal swabs.METHODS This is an observational cohort study.Data collection included information on prisoners who underwent nasopharyngeal swab testing for SARS-CoV-2 and the results.Nasopharyngeal swab tests for SARS-CoV-2 were performed between 15 February 2021 and 31 May 2021 for prisoners with symptoms and all new arrivals to the facility.Another section included information on the diagnosis of the disease according to the International Classification of Diseases,Ninth Revision,and Clinical Modification.RESULTS Up until the 31 May 2021,79.2%of the prisoner cohort(n=1744)agreed to a nasopharyngeal swab test(n=1381).Of these,1288 were negative(93.3%)and 85 were positive(6.2%).A significant association[relative risk(RR)]was found only for the risk of SARS-CoV-2 infection among foreigners compared to Italians[RR=2.4,95%confidence interval(CI):1.2-4.8].A positive association with SARS-CoV-2 infection was also found for inmates with at least one nervous system disorder(RR=4,95%CI:1.8-9.1).The SARS-CoV-2 incidence rate among prisoners is significantly lower than in the general population in Tuscany(standardized incidence ratio 0.7,95%CI:0.6-0.9).CONCLUSION In the prisoner cohort,screening and rapid access to health care for the immigrant population were critical to limiting virus transmission and subsequent morbidity and mortality in this vulnerable population.展开更多
Natural selection opposes the evolution of cooperation unless specific mechanisms are at work in Prisoner's Dilemma. By taking advantage of the modern control theory, the controller design is discussed and the optima...Natural selection opposes the evolution of cooperation unless specific mechanisms are at work in Prisoner's Dilemma. By taking advantage of the modern control theory, the controller design is discussed and the optimal control is designed for promoting cooperation based on the recent advances in mechanisms for the evolution of cooperation. Two con- trol strategies are proposed: compensation control strategy for the cooperator when playing against a defector and reward control strategy for cooperator when playing against a coop- erator. The feasibility and effectiveness of these control strategies for promoting cooperation in different stages are analyzed. The reward for cooperation can't prevent defection from being evolutionary stable strategy (ESS). On the other hand, compensation for the coopera- tor can't prevent defection from emerging and sustaining. By considering the effect and the cost, an optimal control scheme with constraint on the admissible control set is put forward. By analyzing the special nonlinear system of replicator dynamics, the exact analytic solution of the optimal control scheme is obtained based on the maximum principle. Finally, the effectiveness of the proposed method is illustrated by examples.展开更多
This paper studies the evolutionary prisoner's dilemma game on a highly clustered community network in which the clustering coefficient and the community size can be tuned. It finds that the clustering coefficient in...This paper studies the evolutionary prisoner's dilemma game on a highly clustered community network in which the clustering coefficient and the community size can be tuned. It finds that the clustering coefficient in such a degree-homogeneous network inhibits the emergence of cooperation for the entire range of the payoff parameter. Moreover, it finds that the community size can also have a marked influence on the evolution of cooperation, with a larger community size leading to not only a lower cooperation level but also a smaller threshold of the payoff parameter above which cooperators become extinct.展开更多
In this paper, we introduce an asymmetric payoff distribution mechanism into the evolutionary prisoner's dilemma game (PDG) on Newman Watts social networks, and study its effects on the evolution of cooperation. Th...In this paper, we introduce an asymmetric payoff distribution mechanism into the evolutionary prisoner's dilemma game (PDG) on Newman Watts social networks, and study its effects on the evolution of cooperation. The asymmetric payoff distribution mechanism can be adjusted by the parameter α: if α〉 0, the rich will exploit the poor to get richer; if α 〈 0, the rich are forced to offer part of their income to the poor. Numerical results show that the cooperator frequency monotonously increases with c~ and is remarkably promoted when c~ 〉 0. The effects of updating order and self-interaction are also investigated. The co-action of random updating and self-interaction can induce the highest cooperation level. Moreover, we employ the Gini coefficient to investigate the effect of asymmetric payoff distribution on the the system's wealth distribution. This work may be helpful for understanding cooperative behaviour and wealth inequality in society.展开更多
Game theory is extensively used to study strategy-making and actions of play- ers. The authors proposed an analysis method for study the evolutionary outcome and behaviors of players with preference in iterated priso...Game theory is extensively used to study strategy-making and actions of play- ers. The authors proposed an analysis method for study the evolutionary outcome and behaviors of players with preference in iterated prisoner's dilemma. In this article, a preference parameter k was introduced in the payoff matrix, wherein the value of k denotes the player's degree of egoism and altruism (preference). Then, a game-theoretic dynamical model was formulated using Birth-and-Death process. The authors studied how preference influences the evolutionary equilibrium and behaviors of players. The authors get the general results: egoism leads to defection, and altruism can make players build trust and maintain cooperation, and so, the hope of the Pareto optimal solution. In the end, the simulation experiments proved the efficiency of the method.展开更多
This paper studies the long run behavior in evolutionary prisoner's dilemma games. All players are assumed to sit around a circle and to interact only with their neighbors. It is known that full-defection is the uniq...This paper studies the long run behavior in evolutionary prisoner's dilemma games. All players are assumed to sit around a circle and to interact only with their neighbors. It is known that full-defection is the unique long run equilibrium as the probability of players' experimentation (or mutation) tends to zero in the best response dynamics. Here, it is shown that full-cooperation could emerge in the long run if one also cares for his neighbors in the best- response dynamics.展开更多
We study the effect of accumulative payoff on the evolution of cooperation in the evolutionary prisoner's dilemma on a square lattice. We introduce a decaying factor for the accumulative payoff, which characterizes t...We study the effect of accumulative payoff on the evolution of cooperation in the evolutionary prisoner's dilemma on a square lattice. We introduce a decaying factor for the accumulative payoff, which characterizes the extent that the historical payoff is accumulated. It is shown that for fixed values of the temptation to defect, the density of cooperators increases with the value of the decaying factor. This indicates that the more the historical payoff is involved, the more favourable cooperators become. In the critical region where the cooperator density converges to zero, cooperators vanish according to a power-law-like behaviour. The associated exponents agree approximately with the two-dimensional directed percolation and depend weakly on the value of the decaying factor.展开更多
We study evolutionary prisoner's dilemma game on adaptive networks where a population of players co-evolves with their interaction networks. During the co-evolution process, interacted players with opposite strategie...We study evolutionary prisoner's dilemma game on adaptive networks where a population of players co-evolves with their interaction networks. During the co-evolution process, interacted players with opposite strategies either rewire the link between them with probability p or update their strategies with probability 1 - p depending on their payoffs. Numerical simulation shows that the final network is either split into some disconnected communities whose players share the same strategy within each community or forms a single connected network in which all nodes are in the same strategy. Interestingly, the density of cooperators in the final state can be maximised in an intermediate range of p via the competition between time scale of the network dynamics and that of the node dynamics. Finally, the mean-field analysis helps to understand the results of numerical simulation. Our results may provide some insight into understanding the emergence of cooperation in the real situation where the individuals' behaviour and their relationship adaptively co-evolve.展开更多
In this study,we propose a spatial prisoner's dilemma game model with a 2-stage strategy updating rule,and focus on the cooperation behavior of the system.In the first stage,i.e.,the pre-learning stage,a focal player...In this study,we propose a spatial prisoner's dilemma game model with a 2-stage strategy updating rule,and focus on the cooperation behavior of the system.In the first stage,i.e.,the pre-learning stage,a focal player decides whether to update his strategy according to the pre-learning factor β and the payoff difference between himself and the average of his neighbors.If the player makes up his mind to update,he enters into the second stage,i.e.,the learning stage,and adopts a strategy of a randomly selected neighbor according to the standard Fermi updating rule.The simulation results show that the cooperation level has a non-trivial dependence on the pre-learning factor.Generally,the cooperation frequency decreases as the pre-learning factor increases;but a high cooperation level can be obtained in the intermediate region of- 3〈 β 〈-1.We then give some explanations via studying the co-action of pre-learning and learning.Our results may sharpen the understanding of the influence of the strategy updating rule on evolutionary games.展开更多
基金supported by the National Natural Science Foundation(NNSF)of China(61603196,61503079,61520106009,61533008)the Natural Science Foundation of Jiangsu Province of China(BK20150851)+4 种基金China Postdoctoral Science Foundation(2015M581842)Jiangsu Postdoctoral Science Foundation(1601259C)Nanjing University of Posts and Telecommunications Science Foundation(NUPTSF)(NY215011)Priority Academic Program Development of Jiangsu Higher Education Institutions,the open fund of Key Laboratory of Measurement and Control of Complex Systems of Engineering,Ministry of Education(MCCSE2015B02)the Research Innovation Program for College Graduates of Jiangsu Province(CXLX1309)
文摘The iterated prisoner's dilemma(IPD) is an ideal model for analyzing interactions between agents in complex networks. It has attracted wide interest in the development of novel strategies since the success of tit-for-tat in Axelrod's tournament. This paper studies a new adaptive strategy of IPD in different complex networks, where agents can learn and adapt their strategies through reinforcement learning method. A temporal difference learning method is applied for designing the adaptive strategy to optimize the decision making process of the agents. Previous studies indicated that mutual cooperation is hard to emerge in the IPD. Therefore, three examples which based on square lattice network and scale-free network are provided to show two features of the adaptive strategy. First, the mutual cooperation can be achieved by the group with adaptive agents under scale-free network, and once evolution has converged mutual cooperation, it is unlikely to shift. Secondly, the adaptive strategy can earn a better payoff compared with other strategies in the square network. The analytical properties are discussed for verifying evolutionary stability of the adaptive strategy.
文摘Introduction: Hepatitis B virus (HBV) infection is a major public health problem in Cameroon. Garoua city is the headquarters of the North Region of Cameroon, where the HBV prevalence is among the highest of the country. The aim of this study was to determine the prevalence of HBsAg carriage and associated factors among persons incarcerated in the Garoua Central Prison. Methods: It was a cross-sectional study conducted from July 1 to July 31, 2023 at the Garoua Central prison. We included all prisoners willing to participate in the study and who gave their verbal consent. We collected data using a pre-established data entry form and we used rapid test for blood screening for HBV surface antigen (HBs Ag) with ELISA confirmation. Data were analyzed using the R<sup>®</sup> software for Windows. After the univariate analysis, we selected associated variables to HBV infection with p-value p-value was set at 5%. Results: We included 1389 prisoners out of which 97.6% were male. The median age (IQR) of the study population was 28 (23 - 35) years. The median (IQR) duration of incarceration was 12 (6 - 26) months and the mean (±sd) number of incarcerations was 1.24 (±0.6). HBV prevalence was estimated at 14.8% (95% CI: 13.0 - 16.7). Upon uni- and multivariate analysis, no risk factor was significantly associated with viral hepatitis B infection in our study population. Conclusion: The prevalence of Hepatitis B was high in the Garoua Central Prison, but there were no additional risk factors for HBV infection. There is a need to include the Garoua Central Prison and by the way other prisons in the country in the chronic viral hepatitis care program.
文摘BACKGROUND Prisons can be a reservoir for infectious diseases,including severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),due to the very intimate nature of the living spaces and the large number of people forced to share them.AIM To investigate the SARS-CoV-2 epidemiology in prisons,this study evaluated the infection incidence rate in prisoners who underwent nasopharyngeal swabs.METHODS This is an observational cohort study.Data collection included information on prisoners who underwent nasopharyngeal swab testing for SARS-CoV-2 and the results.Nasopharyngeal swab tests for SARS-CoV-2 were performed between 15 February 2021 and 31 May 2021 for prisoners with symptoms and all new arrivals to the facility.Another section included information on the diagnosis of the disease according to the International Classification of Diseases,Ninth Revision,and Clinical Modification.RESULTS Up until the 31 May 2021,79.2%of the prisoner cohort(n=1744)agreed to a nasopharyngeal swab test(n=1381).Of these,1288 were negative(93.3%)and 85 were positive(6.2%).A significant association[relative risk(RR)]was found only for the risk of SARS-CoV-2 infection among foreigners compared to Italians[RR=2.4,95%confidence interval(CI):1.2-4.8].A positive association with SARS-CoV-2 infection was also found for inmates with at least one nervous system disorder(RR=4,95%CI:1.8-9.1).The SARS-CoV-2 incidence rate among prisoners is significantly lower than in the general population in Tuscany(standardized incidence ratio 0.7,95%CI:0.6-0.9).CONCLUSION In the prisoner cohort,screening and rapid access to health care for the immigrant population were critical to limiting virus transmission and subsequent morbidity and mortality in this vulnerable population.
文摘Natural selection opposes the evolution of cooperation unless specific mechanisms are at work in Prisoner's Dilemma. By taking advantage of the modern control theory, the controller design is discussed and the optimal control is designed for promoting cooperation based on the recent advances in mechanisms for the evolution of cooperation. Two con- trol strategies are proposed: compensation control strategy for the cooperator when playing against a defector and reward control strategy for cooperator when playing against a coop- erator. The feasibility and effectiveness of these control strategies for promoting cooperation in different stages are analyzed. The reward for cooperation can't prevent defection from being evolutionary stable strategy (ESS). On the other hand, compensation for the coopera- tor can't prevent defection from emerging and sustaining. By considering the effect and the cost, an optimal control scheme with constraint on the admissible control set is put forward. By analyzing the special nonlinear system of replicator dynamics, the exact analytic solution of the optimal control scheme is obtained based on the maximum principle. Finally, the effectiveness of the proposed method is illustrated by examples.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 70671079, 60674050, 60736022 and 60528007)National 973 Program (Grant No 2002CB312200)+1 种基金National 863 Program (Grant No 2006AA04Z258)11-5 project (Grant NoA2120061303)
文摘This paper studies the evolutionary prisoner's dilemma game on a highly clustered community network in which the clustering coefficient and the community size can be tuned. It finds that the clustering coefficient in such a degree-homogeneous network inhibits the emergence of cooperation for the entire range of the payoff parameter. Moreover, it finds that the community size can also have a marked influence on the evolution of cooperation, with a larger community size leading to not only a lower cooperation level but also a smaller threshold of the payoff parameter above which cooperators become extinct.
基金Project supported by the Major State Basic Research Development Program of China (Grant No. 2004CB318109)Program for New Century Excellent Talents in University of China (Grant No. NCET-07-0787)the National Natural Science Foundation of China (Grant No. 70601026)
文摘In this paper, we introduce an asymmetric payoff distribution mechanism into the evolutionary prisoner's dilemma game (PDG) on Newman Watts social networks, and study its effects on the evolution of cooperation. The asymmetric payoff distribution mechanism can be adjusted by the parameter α: if α〉 0, the rich will exploit the poor to get richer; if α 〈 0, the rich are forced to offer part of their income to the poor. Numerical results show that the cooperator frequency monotonously increases with c~ and is remarkably promoted when c~ 〉 0. The effects of updating order and self-interaction are also investigated. The co-action of random updating and self-interaction can induce the highest cooperation level. Moreover, we employ the Gini coefficient to investigate the effect of asymmetric payoff distribution on the the system's wealth distribution. This work may be helpful for understanding cooperative behaviour and wealth inequality in society.
基金supported by National Natural Science Foundation of China(60574071)
文摘Game theory is extensively used to study strategy-making and actions of play- ers. The authors proposed an analysis method for study the evolutionary outcome and behaviors of players with preference in iterated prisoner's dilemma. In this article, a preference parameter k was introduced in the payoff matrix, wherein the value of k denotes the player's degree of egoism and altruism (preference). Then, a game-theoretic dynamical model was formulated using Birth-and-Death process. The authors studied how preference influences the evolutionary equilibrium and behaviors of players. The authors get the general results: egoism leads to defection, and altruism can make players build trust and maintain cooperation, and so, the hope of the Pareto optimal solution. In the end, the simulation experiments proved the efficiency of the method.
文摘This paper studies the long run behavior in evolutionary prisoner's dilemma games. All players are assumed to sit around a circle and to interact only with their neighbors. It is known that full-defection is the unique long run equilibrium as the probability of players' experimentation (or mutation) tends to zero in the best response dynamics. Here, it is shown that full-cooperation could emerge in the long run if one also cares for his neighbors in the best- response dynamics.
基金supported by the National Natural Science Foundation of China (Grant Nos.70671079,60674050,60736022 and 60528007)the National Basic Research Program of China (Grant No.2002CB312200)+1 种基金the National High Technology Research and Development Program of China (Grant No.2006AA04Z258)11-5 Project (Grant No.A2120061303)
文摘We study the effect of accumulative payoff on the evolution of cooperation in the evolutionary prisoner's dilemma on a square lattice. We introduce a decaying factor for the accumulative payoff, which characterizes the extent that the historical payoff is accumulated. It is shown that for fixed values of the temptation to defect, the density of cooperators increases with the value of the decaying factor. This indicates that the more the historical payoff is involved, the more favourable cooperators become. In the critical region where the cooperator density converges to zero, cooperators vanish according to a power-law-like behaviour. The associated exponents agree approximately with the two-dimensional directed percolation and depend weakly on the value of the decaying factor.
基金Project supported by the National Natural Science Foundation of China (Grant No. 20873130)the Graduate Innovation Fund of USTC
文摘We study evolutionary prisoner's dilemma game on adaptive networks where a population of players co-evolves with their interaction networks. During the co-evolution process, interacted players with opposite strategies either rewire the link between them with probability p or update their strategies with probability 1 - p depending on their payoffs. Numerical simulation shows that the final network is either split into some disconnected communities whose players share the same strategy within each community or forms a single connected network in which all nodes are in the same strategy. Interestingly, the density of cooperators in the final state can be maximised in an intermediate range of p via the competition between time scale of the network dynamics and that of the node dynamics. Finally, the mean-field analysis helps to understand the results of numerical simulation. Our results may provide some insight into understanding the emergence of cooperation in the real situation where the individuals' behaviour and their relationship adaptively co-evolve.
基金Project supported by the Natural Science Foundation of Zhejiang Province of China (Grant Nos. Y1110766,Y1101316,Y6110317,and LY12A05003)the Key Science and Technology Plan Program of Zhejiang Province,China (Grant No. 2010C13021)
文摘In this study,we propose a spatial prisoner's dilemma game model with a 2-stage strategy updating rule,and focus on the cooperation behavior of the system.In the first stage,i.e.,the pre-learning stage,a focal player decides whether to update his strategy according to the pre-learning factor β and the payoff difference between himself and the average of his neighbors.If the player makes up his mind to update,he enters into the second stage,i.e.,the learning stage,and adopts a strategy of a randomly selected neighbor according to the standard Fermi updating rule.The simulation results show that the cooperation level has a non-trivial dependence on the pre-learning factor.Generally,the cooperation frequency decreases as the pre-learning factor increases;but a high cooperation level can be obtained in the intermediate region of- 3〈 β 〈-1.We then give some explanations via studying the co-action of pre-learning and learning.Our results may sharpen the understanding of the influence of the strategy updating rule on evolutionary games.