Modelling crowd dynamics in Bio-PEPA - Extended Abstract

Emergent phenomena occur due to the pattern of non-linear and distributed local interactions between the elements of a system over time. An example of such phenomena is the spontaneous self-organisation of drinking parties in the squares of cities in Spain, also known as ``El Botell'on" (Rowe and Gomez 2003). Surprisingly, crowd models in which the movement of each individual follows a very limited set of simple rules often re-produce quite closely the emergent behaviour of crowds that can be observed in reality. In this paper we take a stochastic process algebraic approach to agent based modelling. In this setting, a single stochastic process algebraic model can be used for several forms of analyses among which simulation, stochastic model-checking and fluid flow analysis. Here we revisit the case of self-organisation of crowds in a city. We show that a fluid flow approximation, i.e. a deterministic reading of the average behaviour of the system, can provide an alternative and efficient way to study the same emergent behaviour as that explored in Rowe and Gomez 2003 where simulation was used instead. Scalability features of this approach may make it particularly useful when studying models of more complex city topologies with very large populations.