Ant Colony Optimization (ACO) is a paradigm for designing metaheuristic algorithms
for combinatorial optimization problems. The first algorithm which can be
classified within this framework was presented in 1991 [21, 13] and, since then,
many diverse variants of the basic principle have been reported in the literature.
The essential trait of ACO algorithms is the combination of a priori information
about the structure of a promising solution with a posteriori information about the
structure of previously obtained good solutions.