Example 1.2 Traveling salesman problem. Perhaps the most popular combinatorial
optimization problem is the traveling salesman problem (TSP). It can be formulated
as follows: given n cities and a distance matrix dn,n, where each element
dij represents the distance between the cities i and j, find a tour that minimizes the
total distance. A tour visits each city exactly once (Hamiltonian cycle) (Figs. 1.4
and 1.5). The size of the search space is n! Table 1.2 shows the combinatorial
explosion of the number of solutions regarding the number of cities. Unfortunately,
enumerating exhaustively all possible solutions is impractical for moderate and large
instances.