  Linking the microscopic and macroscopic behavior is at the heart of many
natural and social sciences. This apparent similarity conceals essential
differences across disciplines: while physical particles are assumed to
optimize the global energy, economic agents maximize their own utility. Here,
we solve exactly a Schelling-like segregation model, which interpolates
continuously between cooperative and individual dynamics. We show that
increasing the degree of cooperativity induces a qualitative transition from a
segregated phase of low utility towards a mixed phase of high utility. By
introducing a simple function which links the individual and global levels, we
pave the way to a rigorous approach of a wide class of systems, where dynamics
is governed by individual strategies.
