Construire des sociétés artificielles pour comprendre les phénomènes sociaux réels

Nous présentons ici rapidement l’approche de modélisation et de simulation multi-agent, ses principales caractéristiques ainsi que son intérêt pour les sciences sociales. En particulier, nous insistons sur la proximité de cette formalisation avec des cadres de pensées classiques en sciences sociales comme l’individualisme méthodologique et nous proposons un usage possible de cette approche comme outil permettant de formaliser et d’interroger les représentations des systèmes sociaux par le scientifique en sciences sociales.We briefly summarize the agent-based modeling and simulation approach, its main characteristics as well as the interest for the social sciences. In particular, we insist on the proximity between such a formalization and some classical frameworks in the social sciences like the methodological individualism. We then propose a use of the agent-based approach as a tool enabling to formalize and investigate the representations of the social systems by the social scientist

An Artificial Stock Market with Interaction Network and Mimetic Agents

Agent-based artificial stock markets attracted much attention over the last years, and many models have been proposed. However, among them, few models take into account the social interactions and mimicking behaviour of traders, while the economic literature describes investors on financial markets as influenced by decisions of their peers and explains that this mimicking behaviour has a decisive impact on price dynamics and market stability. In this paper we propose a continuous double auction model of financial market, populated by heterogeneous traders who interact through a social network of influence. Traders use different investment strategies, namely: fundamentalists who make a decisions based on the fundamental value of assets; hybrids who are initially fundamentalists, but switch to a speculative strategy when they detect an uptrend in prices; noise traders who don’t have sufficient information to take rational decisions, and finally mimetic traders who imitate the decisions of their mentors on the interactions network. An experimental design is performed to show the feasibility and utility of the proposed model

The social fabric of Jeans': Assessing the social: Coupling social simulation and assessment methods

International audienceThe culture and manufacturing of the cotton fabric used to make your Jeans’ may have implied the use of fertilizers or pesticides polluting a water basin, have led to relocating people and even of children labour at different stages of its fabrication. As a consumer you probably didn’t take all these consequences into account (for your sake most of the information is not available, or value-wise you feel unconcerned) and you surely preferred to buy the cheapest one or to follow the fashion trend. Basically, every economic or public activity has repercussions directly, or through a chain of consequences on the environment and the society. In order to try and measure those impacts, or to valuate one choice (Jeans’ L) compared to another (Jeans’ P&J), several assessment methods have been developed and are frequently used. As a self-evident truth, assessment methods are instruments used to evaluate something. These could include measuring a performance on a specific case. In terms of evaluating policies and strategies, their possible outcomes are intended to evaluate their potential impacts. This refers to impact assessment in which past (already implemented actions) or future (ex-ante analysis) performances are studied

The role of network topology on extremism propagation with the Relative Agreement opinion dynamics

In (Deffuant et al., 2002), we proposed a simple model of opinion dynamics, which we used to simulate the influence of extremists in a population. Simulations were run without any specific interaction structure and varying the simulation parameters, we observed different attractors such as predominance of centrism or of extremism. We even observed in certain conditions, that the whole population drifts to one extreme of the opinion, even if initially there are an equal number of extremists at each extreme of the opinion axis. In the present paper, we study the influence of the social networks on the presence of such a dynamical behavior. In particular, we use small-world networks with variable connectivity and randomness of the connections. We find that the drift to a single extreme appears only beyond a critical level of connectivity, which decreases when the randomness increases.Comment: 15 pages, 9 figure

Accès à l’information dans les réseaux sociaux : quelles formes de collaboration ?

National audienceThis paper presents an exploratory analysis attempting to highlight patterns of col- laboration in social medias. Particularly, we focus on crisis management through the Twitter social platform. We rely on two types of crisis: a natural disaster (Sandy hurricane) and a san- itary crisis (Ebola). We proceed in a three step-methodology consisting in 1) analysing the collaboration structure, 2) then identifying topics of collaboration and 3) finally presenting an overview of the latent collaboration network. Results highlight that collaboration is generally performed in a small network while characterized by diversified topics.Nous présentons dans cet article une analyse exploratoire dans l’objectif d’identifier les patrons de collaboration au sein des réseaux sociaux pour l’accès à l’information. Nous nous focalisons sur le cas de la gestion de crise au travers de la plateforme sociale Twitter. Nous nous appuyons ainsi sur deux types de crises : une catastrophe naturelle (l’ouragan Sandy) et une crise sanitaire (Ebola). Nous proposons une méthodologie en trois étapes qui permet 1) d’analyser les structures de collaboration, 2) d’identifier les thématiques de collaboration et 3) de présenter les réseaux latents de collaboration sur l’ensemble du réseau. Les résultats montrent paradoxalement que le périmètre de la collaboration est réduit, que les sujets sous- jacents sont diversifiés et impliquent des utilisateurs qui peuvent être à l’interface de différents sujets

The Results of Meadows and Cliff Are Wrong Because They Compute Indicator y Before Model Convergence

Meadows and Cliff (2012) failed to replicate the results of Deffuant et al. (2002) and concluded that our paper was wrong. In this note, we show that the conclusions of Meadows and Cliff are due to a wrong computation of indicator y, which was not fully specified in our 2002 paper. In particular, Meadows and Cliff compute indicator y before model convergence whereas this indicator should be computed after model convergence

The EUV Sun as the superposition of elementary Suns

International audienceAims. Many studies assume that the solar irradiance in the EUV can be decomposed into different contributions, which makes modelling the spectral variability considerably easier. We consider a different approach in which these contributions are not imposed a priori but effectively and robustly inferred from spectral irradiance measurements. Methods. This is a source separation problem with a positivity constraint, for which we use a Bayesian solution. Results. Using five years of daily EUV spectra recorded by the TIMED/SEE satellite, we show that the spectral irradiance can be decomposed into three elementary spectra. Our results suggest that they describe different layers of the solar atmosphere rather than specific regions. The temporal variability of these spectra is discussed