Orateur
Summary
Abstract. All modelers have come across, one day, one of these popular toy agent-
based models : appearance of pheromone trails built by ants, evolution of social
groups within human populations, formation of arches in granular media. Beside their exemplarity in terms of what can be achieved with ABMs, they are also representative of the way ABMs are designed: in addition to the individual entities employed to represent the system, modelers make implicit references to abstractions corresponding to the emerging structures they are looking after and want to analyze using simulations. Yet, these abstractions are not represented in the models themselves as first-class entities: they are either hidden in ex-post computations or only part of visualization tasks, as if an explicit representation could somehow damage the processes at work in their emergence. We claim that this deliberate choice constitutes an obstacle to the development of multi-level models, where emergence processes are known to occur at different levels of abstraction of the system. This paper describes a modeling language that allows a modeler to represent and specify emergent structures in agent-based models. Firstly, to ease the description, we present these emergent structures and their properties in four agent-based models: Schelling, Boids, Collective Sort and Ants. Then we define the operations that would be needed to represent and specify them explicitly without sacrificing the properties of the original model. An implementation of these operations in the GAML modeling language (part of the GAMA agent-based platform) is then presented. Finally, several simulations of the Boids model are used to illustrate the expressivity of this language and the multiple advantages it brings in terms of analysis, visualization and multi-level modeling of ABMs.
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Vo Duc An, Alexis Drogoul, Jean Daniel Zucker