45,119 research outputs found
Adaptive Boolean Networks and Minority Games with Time--Dependent Capacities
In this paper we consider a network of boolean agents that compete for a
limited resource. The agents play the so called Generalized Minority Game where
the capacity level is allowed to vary externally. We study the properties of
such a system for different values of the mean connectivity of the network,
and show that the system with K=2 shows a high degree of coordination for
relatively large variations of the capacity level.Comment: 4 pages, 4 figure
Acquaintance role for decision making and exchanges in social networks
We model a social network by a random graph whose nodes represent agents and
links between two of them stand for a reciprocal interaction; each agent is
also associated to a binary variable which represents a dichotomic opinion or
attribute. We consider both the case of pair-wise (p=2) and multiple (p>2)
interactions among agents and we study the behavior of the resulting system by
means of the energy-entropy scheme, typical of statistical mechanics methods.
We show, analytically and numerically, that the connectivity of the social
network plays a non-trivial role: while for pair-wise interactions (p=2) the
connectivity weights linearly, when interactions involve contemporary a number
of agents larger than two (p>2), its weight gets more and more important. As a
result, when p is large, a full consensus within the system, can be reached at
relatively small critical couplings with respect to the p=2 case usually
analyzed, or, otherwise stated, relatively small coupling strengths among
agents are sufficient to orient most of the system.Comment: 7 pages, 1 figur
Phase transitions in crowd dynamics of resource allocation
We define and study a class of resources allocation processes where
agents, by repeatedly visiting resources, try to converge to optimal
configuration where each resource is occupied by at most one agent. The process
exhibits a phase transition, as the density of agents grows, from an
absorbing to an active phase. In the latter, even if the number of resources is
in principle enough for all agents (), the system never settles to a
frozen configuration. We recast these processes in terms of zero-range
interacting particles, studying analytically the mean field dynamics and
investigating numerically the phase transition in finite dimensions. We find a
good agreement with the critical exponents of the stochastic fixed-energy
sandpile. The lack of coordination in the active phase also leads to a
non-trivial faster-is-slower effect.Comment: 7 pages, 7 fig
Evolution of Market Heuristics
The time evolution of aggregate economic variables, such as stock prices, is affected by market expectations of individual investors. Neo-classical economic theory assumes that individuals form expectations rationally, thus enforcing prices to track economic fundamentals and leading to an efficient allocation of resources. However, laboratory experiments with human subjects have shown that individuals do not behave fully rational but instead follow simple heuristics. In laboratory markets prices may show persistent deviations from fundamentals similar to the large swings observed in real stock prices. Here we show that evolutionary selection among simple forecasting heuristics can explain coordination of individual behavior leading to three different aggregate outcomes observed in recent laboratory market forecasting experiments: slow monotonic price convergence, oscillatory dampened price fluctuations and persistent price oscillations. In our model forecasting strategies are selected every period from a small population of plausible heuristics, such as adaptive expectations and trend following rules. Individuals adapt their strategies over time, based on the relative forecasting performance of the heuristics. As a result, the evolutionary switching mechanism exhibits path dependence and matches individual forecasting behavior as well as aggregate market outcomes in the experiments. Our results are in line with recent work on agent-based models of interaction and contribute to a behavioral explanation of universal features of financial markets.
Irrelevance of memory in the minority game
By means of extensive numerical simulations we show that all the distinctive
features of the minority game introduced by Challet and Zhang (1997), are
completely independent from the memory of the agents. The only crucial
requirement is that all the individuals must posses the same information,
irrespective of the fact that this information is true or false.Comment: 4 RevTeX pages, 4 figure
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