  The image of physics is connected with simple "mechanical" deterministic
events: that an apple always falls down, that force equals mass times
acceleleration. Indeed, applications of such concept to social or historical
problems go back two centuries (population growth and stabilisation, by Malthus
and by Verhulst) and use "differential equations", as recently revierwed by
Vitanov and Ausloos [2011]. However, since even today's computers cannot follow
the motion of all air molecules within one cubic centimeter, the probabilistic
approach has become fashionable since Ludwig Boltzmann invented Statistical
Physics in the 19th century. Computer simulations in Statistical Physics deal
with single particles, a method called agent-based modelling in fields which
adopted it later. Particularly simple are binary models where each particle has
only two choices, called spin up and spin down by physicists, bit zero and bit
one by computer scientists, and voters for the Republicans or for the Democrats
in American politics (where one human is simulated as one particle).
Neighbouring particles may influence each other, and the Ising model of 1925 is
the best-studied example of such models. This text will explain to the reader
how to program the Ising model on a square lattice (in Fortran language);
starting from there the readers can build their own computer programs. Some
applications of Statistical Physics outside the natural sciences will be
listed.
