A Game perspective to complex adaptive systems

Understanding the behaviour of a system through the properties of the elements of the system is a central problem in several fields of contemporary research. Appealing approaches for gaining such understanding have been proposed in complex systems studies. One particular approach is based on the scheme of agent-based modelling, in which the elements of the system are described by a set of precise rules which are implemented by computer programs. This dissertation is focused on topics related to two types of agent-based models: minority games and spatial two player games. The first part of the thesis deals with minority games that have been extensively studied in the physics literature during the past eight years. A minority game describes a society of adaptive individuals with bounded rationality competing for scarce resources. Questions arising from such a model are associated with the efficiency of the system and the success of its individuals in utilizing the scarce resources. Previous studies have indicated that in case the individuals are allowed to evolve, they tend to evolve such that the efficiency of the system improves. However, the actual level of efficiency substantially depends on the type of evolution present in the system. We have applied genetic algorithms to make the system evolving. Our results indicate that natural selection and genetic algorithms can lead the system perform optimally and increase the success of individuals remarkably. The second part of the thesis describes aspects of games that model strategic interaction situations between individuals. Especially, the focus of this part of the thesis is on models that aim at explaining the emergence and persistence of cooperative behaviour in an animal or human society. Previous studies have indicated that spatial structure of the society largely contributes to the maintenance of cooperation in these models. However, much of the research has been carried out by relying on evolutionary dynamics of the society associated with changes occurring in long times. We have explored a spatial game by allowing the individuals in the system be adaptive and act on short times, and our results show that the characteristic behaviour of the system is different from that observed in studies using evolutionary dynamics.reviewe

Biology helps you to win a game

We present a game of interacting agents which mimics the complex dynamics found in many natural and social systems. These agents modify their strategies periodically, depending on their performances using genetic crossover mechanisms, inspired by biology. We study the performances of the agents under different conditions, and how they adapt themselves. In addition the dynamics of the game is investigated.Comment: 4 pages including 6 figures. Uses REVTeX4. Submitted for Conference Proceedings of the "Unconventional Applications of Statistical Physics", Kolkat

Intelligent Minority Game with genetic-crossover strategies

We develop a game theoretical model of $N$ heterogeneous interacting agents called the intelligent minority game. The ``intelligent'' agents play the basic minority game and depending on their performances, generate new strategies using the one-point genetic crossover mechanism. The performances change dramatically and the game moves rapidly to an efficient state (fluctuations in the number of agents performing a particular action, characterized by $\sigma^2$, reaches a low value). There is no ``phase transition'' when we vary $\sigma^2/N$ with $2^M/N$, where $M$ is the ``memory''of an agent.Comment: 4 pages, 5 encapsulated postscript figures. Uses RevTex

Spatial snowdrift game with myopic agents

We have studied a spatially extended snowdrift game, in which the players are located on the sites of two-dimensional square lattices and repeatedly have to choose one of the two strategies, either cooperation (C) or defection (D). A player interacts with its nearest neighbors only, and aims at playing a strategy which maximizes its instant pay-off, assuming that the neighboring agents retain their strategies. If a player is not content with its current strategy, it will change it to the opposite one with probability $p$ next round. Here we show through simulations and analytical approach that these rules result in cooperation levels, which differ to large extent from those obtained using the replicator dynamics.Comment: 13 pages, 5 figure

Searching for good strategies in adaptive minority games

In this paper we introduce and study various adaptive minority game models in which agents try to improve their performances by modifying their strategies through genetic algorithm based crossover mechanism. One aim of this study is to find out what happens at the system as well as at the individual agent level. Adaptation is found to improve the performance of individual agents quite remarkably, to tighten the competition among the agents, and to drive the whole system towards maximum efficiency. Results from four adaptative minority games and the basic minority game are compared, and the parameter dependencies of the best performing game are discussed

Searching good strategies in adaptive minority games

In this paper we introduce adaptation mechanism based on genetic algorithms in minority games. If agents find their performances too low, they modify their strategies in hope to improve their performances and become more successful. One aim of this study is to find out what happens at the system as well as at the individual agent level. We observe that adaptation remarkably tightens the competition among the agents, and tries to pull the collective system into a state where the aggregate utility is the largest. We first make a brief comparative study of the different adaptation mechanisms and then present in more detail parametric studies. These different adaptation mechanisms broaden the scope of the applications of minority games to the study of complex systems.Comment: 8 pages including 9 figures. Uses REVTeX

Gender-dependent progression of systemic metabolic states in early childhood

Little is known about the human intra-individual metabolic profile changes over an extended period of time. Here, we introduce a novel concept suggesting that children even at a very young age can be categorized in terms of metabolic state as they advance in development. The hidden Markov models were used as a method for discovering the underlying progression in the metabolic state. We applied the methodology to study metabolic trajectories in children between birth and 4 years of age, based on a series of samples selected from a large birth cohort study. We found multiple previously unknown age- and gender-related metabolome changes of potential medical significance. Specifically, we found that the major developmental state differences between girls and boys are attributed to sphingolipids. In addition, we demonstrated the feasibility of state-based alignment of personal metabolic trajectories. We show that children have different development rates at the level of metabolome and thus the state-based approach may be advantageous when applying metabolome profiling in search of markers for subtle (patho)physiological changes

Gender, Contraceptives and Individual Metabolic Predisposition Shape a Healthy Plasma Lipidome

Lipidomics of human blood plasma is an emerging biomarker discovery approach that compares lipid profiles under pathological and physiologically normal conditions, but how a healthy lipidome varies within the population is poorly understood. By quantifying 281 molecular species from 27 major lipid classes in the plasma of 71 healthy young Caucasians whose 35 clinical blood test and anthropometric indices matched the medical norm, we provided a comprehensive, expandable and clinically relevant resource of reference molar concentrations of individual lipids. We established that gender is a major lipidomic factor, whose impact is strongly enhanced by hormonal contraceptives and mediated by sex hormone-binding globulin. In lipidomics epidemiological studies should avoid mixed-gender cohorts and females taking hormonal contraceptives should be considered as a separate sub-cohort. Within a gender-restricted cohort lipidomics revealed a compositional signature that indicates the predisposition towards an early development of metabolic syndrome in ca. 25% of healthy male individuals suggesting a healthy plasma lipidome as resource for early biomarker discovery