  The Schelling model of 1971 is a complicated version of a square-lattice
Ising model at zero temperature, to explain urban segregation, based on the
neighbour preferences of the residents, without external reasons. Various
versions between Ising and Schelling models give about the same results.
Inhomogeneous "temperatures" T do not change the results much, while a feedback
between segregation and T leads to a self-organisation of an average T.
