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Horacio Ceva

Publications and source records attributed to Horacio Ceva.

At least 19 recordsLinked to original sources
arXiv2014

Entropic determination of the phase transition in a coevolving opinion-formation model

We study an opinion formation model by the means of a co-evolving complex network where the vertices represent the individuals, characterised by their evolving opinions, and the edges represent the interactions among them. The network adapts to the spreading of opinions in two ways: not only connected agents interact and eventually change their thinking but an agent may also rewire one of its links to a neighborhood holding the same opinion as his. The dynamics depends on an external parameter Φ, which controls the plasticity of the network. We show how the information entropy associated to the distribution of group sizes, allows to locate the phase transition between full consensus and a society where different opinions coexist. We also determine the minimum size of the most informative sampling. At the transition the distribution of the sizes of groups holding the same opinion is scale free.

physics.soc-ph↗
arXiv2011

Does Phylogenetic Proximity Explain Nestedness in Mutualistic Ecosystems?

We investigate how the pattern of contacts between species in mutualistic ecosystems is affected by the phylogenetic proximity between the species of each guild. We develop a dynamical model geared to establish the role of such proximity in the emergence of a nested pattern of contacts. We also define a parameter that provides a direct measure of the influence of phylogenetic proximity in a given pattern of contacts. We conclude that although phylogenetic proximity is compatible with nestedness it can not be claimed to be a cause of it. We find that nestedness can instead be attributed to a general rule by which species tend to hold contacts with counterparts that already have a large number of contacts. If the phylogenetic structure of both guilds is brought into the analysis, this rule is equivalent to maximize the phylogenetic diversity of the mutualistic counterparts of species of either guild.

q-bio.PE↗
arXiv2010

Phylogenetic Proximity and Nestedness in Mutualistic Ecosystems

We investigate how the pattern of contacts between species in mutualistic ecosystems is affected by the phylogenetic proximity between the species of each guild. We develop several theoretical tools to measure that effect and we use them to examine some real mutualistic sytems. We aim at establishing the role of such proximity in the emergence of a nested pattern of contacts. We conclude that although phylogenetic proximity is compatible with nestedness it can not be claimed to determine it. We find that nestedness can instead be attributed to a general rule by which species tend to behave as generalists holding contacts with counterparts that already have a large number of contacts. A nested ecosystem generated by this rule, shows high phylogenetic diversity. This is to say, the counterparts of species having similar degrees are not phylogenetic neighbours.

q-bio.PE↗
arXiv2008

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.

physics.soc-ph↗
arXiv2008

Two classes of bipartite networks: nested biological and social systems

Bipartite graphs have received some attention in the study of social networks and of biological mutualistic systems. A generalization of a previous model is presented, that evolves the topology of the graph in order to optimally account for a given Contact Preference Rule between the two guilds of the network. As a result, social and biological graphs are classified as belonging to two clearly different classes. Projected graphs, linking the agents of only one guild, are obtained from the original bipartite graph. The corresponding evolution of its statistical properties is also studied. An example of a biological mutualistic network is analyzed in great detail, and it is found that the model provides a very good quantitative fitting of its properties. The model also provides a proper qualitative description of the statistical features observed in social webs, suggesting the possible reasons underlying the difference in the organization of these two kinds of bipartite networks.

physics.soc-ph↗
arXiv2008

On the application of the Critical Minimum Energy Subspace method to disordered systems

We discuss the recent application to strongly disordered systems of the Critical Minimum Energy Subspace (CMES) method, used to limit the energy subspace of the Wang-Landau sampling. We compare with our results on the 3D Random Field Ising Model obtained by a multi-range Wang-Landau simulation in the whole energy range. We point out at some problems that may arise when applying the CMES scheme to models having a complex free energy landscape. PACS numbers: 02.70.Tt,02.70.Rr,05.50.+q, 64.60.Cn, 64.60.Fr, 75.10.Hk

cond-mat.stat-mech↗
arXiv2008

The underlying complex network of the Minority Game

We study the structure of the underlying network of connections in the Minority Game. There is not an explicit interaction among the agents, but they interact via global magnitudes of the model and mainly through their strategies. We define a link between two agents by quantifying the similarity among their strategies, and analyze the structure of the resulting underlying complex networks as a function of the number of agents in the game and the value of the agents' memory, in games with two strategies per player. We characterize the different phases of this system with networks with different properties, for this link definition. Thus, the Minority Game phase characterized by the presence of crowds can be identified with a small world network, while the phase with the same results as a random decision game as a random network. Finally, we use the Full Strategy Minority Game model, to explicitly calculate some properties of its networks, such as the degree distribution, for the same link definition, and to estimate, from them, the properties of the networks of the Minority Game, obtaining a very good agreement with its measured properties.

physics.soc-ph↗
arXiv2007

Wang-Landau study of the critical behaviour of the bimodal 3D-Random Field Ising Model

We apply the Wang-Landau method to the study of the critical behaviour of the three dimensional Random Field Ising Model with a bimodal probability distribution. Our results show that for high values of the random field intensity the transition is first order, characterized by a double-peaked energy probability distribution at the transition temperature. On the other hand, the transition looks continuous for low values of the field intensity. In spite of the large sample to sample fluctuations observed, the double peak in the probability distribution is always present for high fields

cond-mat.stat-mech↗
arXiv2007

Analysis and Assembling of Network Structure in Mutualistic Systems

It has been observed that mutualistic bipartite networks have a nested structure of interactions. In addition, the degree distributions associated with the two guilds involved in such networks (e.g. plants & pollinators or plants & seed dispersers) approximately follow a truncated power law. We show that nestedness and truncated power law distributions are intimately linked, and that any biological reasons for such truncation are superimposed to finite size effects . We further explore the internal organization of bipartite networks by developing a self-organizing network model (SNM) that reproduces empirical observations of pollination systems of widely different sizes. Since the only inputs to the SNM are numbers of plant and animal species, and their interactions (i.e., no data on local abundance of the interacting species are needed), we suggest that the well-known association between species frequency of interaction and species degree is a consequence rather than a cause, of the observed network structure.

q-bio.PE↗
arXiv2004

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.

cond-mat.stat-mech↗
arXiv2004

The Minority Game with interactions

We partially modify the rules of the Minority Game (MG) by introducing some degree of local information in the game, which is only available for some agents, called the interacting agents. Our work shows that, for small values of the new parameter of the model (the fraction of interacting agents), there is an improvement of the use of the resources with respect to the MG, while as this number grows the response of the system changes, and ends up behaving worst than the usual MG.

cond-mat.stat-mech↗
arXiv2003

The evolutionary minority game with local coordination

We discuss 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 neighborhood. We report numerical results for the topologies of a ring, a torus and a random graph changing the size of the neighborhood. We find the surprising result that in the EMG a better coordination (a lower frustration) can be achieved if all agents base their actions on local information disregarding the global trend in the self-segregation process.

cond-mat↗
arXiv2002

Minority Game: a mean-field-like approach

We calculate the standard deviation of (N1-N0), the difference of the number of agents choosing between the two alternatives of the minority game. Our approach is based on two approximations: we use the whole set of possible strategies, rather than only those distributed between the agents involved in a game; moreover, we assume that a period-two dynamics discussed by previous authors is appropiate within the range of validity of our work. With these approximations we introduce a set of states of the system, and are able to replace time averages by ensamble averages over these states. Our results show very good agreement with simulations results for most part of the informationally efficient phase.

cond-mat↗
arXiv2001

Thermal treatment of the minority game

We study a cost function for the aggregate behavior of all the agents involved in the Minority Game (MG) or the Bar Attendance Model (BAM). The cost function allows to define a deterministic, synchronous dynamics that yields results that have the main relevant features than those of the probabilistic, sequential dynamics used for the MG or the BAM. We define a temperature through a Langevin approach in terms of the fluctuations of the average attendance. We prove that the cost function is an extensive quantity that can play the role of an internal energy of the many agent system while the temperature so defined is an intensive parameter. We compare the results of the thermal perturbation to the deterministic dynamics and prove that they agree with those obtained with the MG or BAM in the limit of very low temperature.

cond-mat↗
arXiv2000

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 BAM

cond-mat↗