Bounded confidence and Social networks

In the so-called bounded confidence model proposed by Deffuant et al, agents can influence each other's opinion provided that opinions are already sufficiently close enough. We here discuss the influence of possible social networks topologies on the dynamics of this model.Comment: proceedings COSIN meeting Roma, 9/2003 sub. Eur. J. Phys

Production networks and failure avalanches

Although standard economics textbooks are seldom interested in production networks, modern economies are more and more based upon suppliers/customers interactions. One can consider entire sectors of the economy as generalised supply chains. We will take this view in the present paper and study under which conditions local failures to produce or simply to deliver can result in avalanches of shortage and bankruptcies across the network. We will show that a large class of models exhibit scale free distributions of production and wealth among firms and that metastable regions of high production are highly localised

Interacting Agents and Continuous Opinions Dynamics

We present a model of opinion dynamics in which agents adjust continuous opinions as a result of random binary encounters whenever their difference in opinion is below a given threshold. High thresholds yield convergence of opinions towards an average opinion, whereas low thresholds result in several opinion clusters. The model is further generalised to network interactions, threshold heterogeneity, adaptive thresholds and binary strings of opinions.Comment: 21 pages, 13 figures. http://www.lps.ens.fr/~weisbuch/contopidyn/contopidyn.htm

Spread of decisions in the corporate board network

Boards of large corporations sharing some of their directors are connected in complex networks. Boards are responsible for corporations' long-term strategy and are often involved in decisions about a common topic related to the belief in economical growth or recession. We are interested in understanding under which conditions a large majority of boards making a same decision can emerge in the network. We present a model where board directors are engaged in a decision making dynamics based on "herd behavior". Boards influence each other through shared directors. We find that imitation of colleagues and opinion bias due to the interlock do not trigger an avalanche of identical decisions over the board network, whereas the information about interlocked boards' decisions does. There is no need to invoke global public information, nor external driving forces. This model provides a simple endogenous mechanism to explain the fact that boards of the largest corporations of a country can, in the span of a few months, take the same decisions about general topics.Comment: to appear in Advances in Complex Systems, accepted on 27 Nov 200

Market Organization

In standard economic theory, mechanisms like Adam Smith's "invisible hand" or the Walrasian auctioneer balance aggregate demand and supply and match individuals such that the market clears. Usually, some kind of price adjustment process is assumed without specifying how the implied transactions are organized. In real markets, price adjustment and the matching of buyers and sellers involve considerable exchange of information. Past experience plays an important role in partner selection and in deciding whether a suggested transaction is accepted or not. This implies a process of learning about trading partners and opportunities. The model suggested here, explains how this learning leads to market organization (loyality) or a lack thereof (searching). A decentralized market of a perishable good is considered, where past experience governs the choice of trading partner. Depending on how important past payoffs are and how long the memory is, and depending on the number of players in the market, buyers decide to search or to be loyal. The transition from searching to loyality is very abrupt and resembles phase transitions known from statistical physics. Simulations and empirical evidence from the Marseille wholesale fish market confirm the co-existence of the two behavioral patterns of buyers and the importance of past experience of their behavior.Decentralized Markets, Market Organization, Reinforcement Learning, Matching, Search, Price Distribution.

Social percolation models

Abstract We here relate the occurrence of extreme market shares, close to either 0 or 100%, in the media industry to a percolation phenomenon across the social network of customers. We further discuss the possibility of observing self-organized criticality when customers and cinema producers adjust their preferences and the quality of the produced ÿlms according to previous experience. Comprehensive computer simulations on square lattices do indeed exhibit self-organized criticality towards the usual percolation threshold and related scaling behaviour

Singularités, sens et universalité, Rochebrune 2015

International audienceMise au point sur les relations entre singularités en théorie des sytèmes dynamiques ettransitions de phases en mécanique statistique. Classes d'universalité et stabilité structurelle