# Jane Hillston

0.05 makes a crowd!

Process algebra has traditionally been given a discrete state space semantics in terms of labelled transition systems, and, in the case of stochastic process algebras, continuous time Markov processes. However recent work on the fluid approximation of these discrete models has opened a new realm of applications for process algebras, allowing us to study the collective behaviour of large populations of entities.

In this talk I will discuss some recent work on modelling the behaviour of human crowds using the stochastic process algebra Bio-PEPA.

The old adage says that "3 makes a crowd" but I will show how, if we consider a population of 60 people moving around four city squares, the crucial parameter value is 0.05.