Threshold, noise and adaptation in multi agent reactive systems

Nadav Shnerb

Department of Physics, Bar-Ilan University, Ramat-Gan 52900, Israel

The failure of the continuum (partial differential equations) approach to appropriately describe multi agent systems is discussed. In the first example, adaptation of autocatalytic fluctuations to diffusive noise, growth rate fluctuations induced by the discrete nature of the agents are shown to allow for an active phase, where reactants proliferate as their spatial configuration adapts to the fluctuations of the catalyst density. The second example is vegetation pattern formation in the semi-arid climatic zone, where threshold for the biomass of the perennial flora is shown to be a crucial factor, leading to a frozen disordered patterns in a "glassy" state.