Quenching and Annealing in the Minority Game

We report the occurrence of quenching and annealing in a version of the Minority Game (MG) in which the winning option is to join a given fraction of the population that is a free, external parameter. We compare this to the different dynamics of the Bar Attendance Model (BAM) where the updating of the attendance strategy makes use of all available information about the system and quenching does not occur. We provide an annealing schedule by which the quenched configuration of the MG reaches equilibrium and coincides with the one obtained with the BAMComment: 8 pages, 4 figure

Understanding and characterizing nestedness in mutualistic bipartite networks

In this work we present a dynamical model that succesfully describes the organization of mutualistic ecological systems. The main characteristic of these systems is the nested structure of the bipartite adjacency matrix describing their interactions. We introduce a nestedness coefficient, as an alternative to the Atmar and Patterson temperature, commonly used to measure the nestedness degree of the network. This coefficient has the advantage of being based on the robustness of the ecological system and it is not only describing the ordering of the bipartite matrix but it is also able to tell the difference, if any, between the degree of organization of each guild.Comment: oral talk in Computer Physics Conference CCP2008, Brazi

Order and disorder in the Local Evolutionary Minority Game

We study a modification of the Evolutionary Minority Game (EMG) in which agents are placed in the nodes of a regular or a random graph. A neighborhood for each agent can thus be defined and a modification of the usual relaxation dynamics can be made in which each agent updates her decision scheme depending upon the options made in her immediate neighborhood. We name this model the Local Evolutionary Minority Game (LEMG). We report numerical results for the topologies of a ring, a torus and a random graph changing the size of the neighborhood. We focus our discussion in a one dimensional system and perform a detailed comparison of the results obtained from the random relaxation dynamics of the LEMG and from a linear chain of interacting spin-like variables at a finite temperature. We provide a physical interpretation of the surprising result that in the LEMG a better coordination (a lower frustration) is achieved if agents base their actions on local information. We show how the LEMG can be regarded as a model that gradually interpolates between a fully ordered, antiferromagnetic system and a fully disordered system that can be assimilated to a spin glass.Comment: 12 pages, 8 figures, RevTex; omission of a relevant reference correcte