1. Optimal distribution of incentives for public cooperation in heterogeneous interaction environmentsXiaojie Chen, Matjaž Perc, 2014, izvirni znanstveni članek Opis: In the framework of evolutionary games with institutional reciprocity, limited incentives are at disposal for rewarding cooperators and punishing defectors. In the simplest case, it can be assumed that, depending on their strategies, all players receive equal incentives from the common pool. The question arises, however, what is the optimal distribution of institutional incentives? How should we best reward and punish individuals for cooperation to thrive? We study this problem for the public goods game on a scalefree network. We show that if the synergetic effects of group interactions are weak, the level of cooperation in the population can be maximized simply by adopting the simplest "equal distribution" scheme. If synergetic effects are strong, however, it is best to reward highdegree nodes more than lowdegree nodes. These distribution schemes for institutional rewards are independent of payoff normalization. For institutional punishment, however, the same optimization problem is more complex, and its solution depends on whether absolute or degreenormalized payoffs are used. We find that degreenormalized payoffs require highdegree nodes be punished more lenient than lowdegree nodes. Conversely, if absolute payoffs count, then highdegree nodes should be punished stronger than lowdegree nodes. Ključne besede: public cooperation, institutional reciprocity, scalefree network, punishment, reward Objavljeno v DKUM: 10.07.2017; Ogledov: 835; Prenosov: 353 Celotno besedilo (3,26 MB) Gradivo ima več datotek! Več...

2. Probabilistic sharing solves the problem of costly punishmentXiaojie Chen, Attila Szolnoki, Matjaž Perc, 2014, izvirni znanstveni članek Opis: Cooperators that refuse to participate in sanctioning defectors create the secondorder freerider problem. Such cooperators will not be punished because they contribute to the public good, but they also eschew the costs associated with punishing defectors. Altruistic punishers  those that cooperate and punish  are at a disadvantage, and it is puzzling how such behaviour has evolved. We show that sharing the responsibility to sanction defectors rather than relying on certain individuals to do so permanently can solve the problem of costly punishment. Inspired by the fact that humans have strong but also emotional tendencies for fair play, we consider probabilistic sanctioning as the simplest way of distributing the duty. In wellmixed populations the public goods game is transformed into a coordination game with full cooperation and defection as the two stable equilibria, while in structured populations pattern formation supports additional counterintuitive solutions that are reminiscent of Parrondoʼs paradox. Ključne besede: social dynamics, networks, punishment, public goods, econophysics Objavljeno v DKUM: 03.07.2017; Ogledov: 735; Prenosov: 337 Celotno besedilo (1,52 MB) Gradivo ima več datotek! Več...

3. Excessive abundance of common resources deters social responsibilityXiaojie Chen, Matjaž Perc, 2014, izvirni znanstveni članek Opis: We study the evolution of cooperation in the collectiverisk social dilemma game, where the risk is determined by a collective target that must be reached with individual contributions. All players initially receive endowments from the available amount of common resources. While cooperators contribute part of their endowment to the collective target, defectors do not. If the target is not reached, the endowments of all players are lost. In our model, we introduce a feedback between the amount of common resources and the contributions of cooperators. We show that cooperation can be sustained only if the common resources are preserved but never excessively abound. This, however, requires a delicate balance between the amount of common resources that initially exist, and the amount cooperators contribute to the collective target. Exceeding critical thresholds in either of the two amounts leads to loss of cooperation, and consequently to the depletion of common resources. Ključne besede: social dilemma, evolutionary games, public goods, abundance, phase transitions, physics of social systems Objavljeno v DKUM: 23.06.2017; Ogledov: 1164; Prenosov: 333 Celotno besedilo (950,12 KB) Gradivo ima več datotek! Več...

4. Evolution of public cooperation in a monitored society with implicated punishment and withingroup enforcementXiaojie Chen, Tatsuya Sasaki, Matjaž Perc, 2015, izvirni znanstveni članek Opis: Monitoring with implicated punishment is common in human societies to avert freeriding on common goods. But is it effective in promoting public cooperation? We show that the introduction of monitoring and implicated punishment is indeed effective, as it transforms the public goods game to a coordination game, thus rendering cooperation viable in infinite and finite wellmixed populations. We also show that the addition of withingroup enforcement further promotes the evolution of public cooperation. However, although the group size in this context has nonlinear effects on collective action, an intermediate group size is least conductive to cooperative behaviour. This contradicts recent field observations, where an intermediate group size was declared optimal with the conjecture that groupsize effects and withingroup enforcement are responsible. Our theoretical research thus clarifies key aspects of monitoring with implicated punishment in human societies, and additionally, it reveals fundamental groupsize effects that facilitate prosocial collective action. Ključne besede: cooperation, public goods, punishment, sustainable development, physics of social systems Objavljeno v DKUM: 23.06.2017; Ogledov: 717; Prenosov: 335 Celotno besedilo (1,50 MB) Gradivo ima več datotek! Več...

5. Beyond pairwise strategy updating in the prisoner's dilemma gameXiaofeng Wang, Matjaž Perc, Yongkui Liu, Xiaojie Chen, Long Wang, 2012, izvirni znanstveni članek Opis: In spatial games players typically alter their strategy by imitating the most successful or one randomly selected neighbor. Since a single neighbor is taken as reference, the information stemming from other neighbors is neglected, which begets the consideration of alternative, possibly more realistic approaches. Here we show that strategy changes inspired not only by the performance of individual neighbors but rather by entire neighborhoods introduce a qualitatively different evolutionary dynamics that is able to support the stable existence of very small cooperative clusters. This leads to phase diagrams that differ significantly from those obtained by means of pairwise strategy updating. In particular, the survivability of cooperators is possible even by high temptations to defect and over a much wider uncertainty range. We support the simulation results by means of pair approximations and analysis of spatial patterns, which jointly highlight the importance of local information for the resolution of social dilemmas. Ključne besede: cooperation, social dilemma, wisdom of crowds, phase transitions, physics of social systems Objavljeno v DKUM: 23.06.2017; Ogledov: 592; Prenosov: 301 Celotno besedilo (825,96 KB) Gradivo ima več datotek! Več...

6. Winstayloselearn promotes cooperation in the spatial prisoner's dilemma gameYongkui Liu, Xiaojie Chen, Lin Zhang, Long Wang, Matjaž Perc, 2012, izvirni znanstveni članek Opis: Holding on to one's strategy is natural and common if the later warrants success and satisfaction. This goes against widespread simulation practices of evolutionary games, where players frequently consider changing their strategy even though their payoffs may be marginally different than those of the other players. Inspired by this observation, we introduce an aspirationbased winstayloselearn strategy updating rule into the spatial prisoner's dilemma game. The rule is simple and intuitive, foreseeing strategy changes only by dissatisfied players, who then attempt to adopt the strategy of one of their nearest neighbors, while the strategies of satisfied players are not subject to change. We find that the proposed winstayloselearn rule promotes the evolution of cooperation, and it does so very robustly and independently of the initial conditions. In fact, we show that even a minute initial fraction of cooperators may be sufficient to eventually secure a highly cooperative final state. In addition to extensive simulation results that support our conclusions, we also present results obtained by means of the pair approximation of the studied game. Our findings continue the success story of related winstay strategy updating rules, and by doing so reveal new ways of resolving the prisoner's dilemma. Ključne besede: social dilemmas, prisoner's dilemma, cooperation, networks Objavljeno v DKUM: 19.06.2017; Ogledov: 776; Prenosov: 311 Celotno besedilo (390,56 KB) Gradivo ima več datotek! Več...

7. Adaptive and bounded investment returns promote cooperation in spatial public goods gamesXiaojie Chen, Yongkui Liu, Yonghui Zhou, Long Wang, Matjaž Perc, 2012, izvirni znanstveni članek Opis: The public goods game is one of the most famous models for studying the evolution of cooperation in sizable groups. The multiplication factor in this game can characterize the investment return from the public good, which may be variable depending on the interactive environment in realistic situations. Instead of using the same universal value, here we consider that the multiplication factor in each group is updated based on the differences between the local and global interactive environments in the spatial public goods game, but meanwhile limited to within a certain range. We find that the adaptive and bounded investment returns can significantly promote cooperation. In particular, full cooperation can be achieved for high feedback strength when appropriate limitation is set for the investment return. Also, we show that the fraction of cooperators in the whole population can become larger if the lower and upper limits of the multiplication factor are increased. Furthermore, in comparison to the traditionally spatial public goods game where the multiplication factor in each group is identical and fixed, we find that cooperation can be better promoted if the multiplication factor is constrained to adjust between one and the group size in our model. Our results highlight the importance of the locally adaptive and bounded investment returns for the emergence and dominance of cooperative behavior in structured populations. Ključne besede: cooperation, public goods, social dilemmas, physics of social systems Objavljeno v DKUM: 19.06.2017; Ogledov: 686; Prenosov: 355 Celotno besedilo (590,51 KB) Gradivo ima več datotek! Več...
