Once a tour has been generated by some tour construction
heuristic, we might wish to improve that solution.
There are several ways to do this, but the most
common ones are the 2-opt and 3-opt local searches.
Their performances are somewhat linked to the construction
heuristic used.
Other ways of improving our solution is to do a tabu
search using 2-opt and 3-opt moves. Simulated annealing
also use these moves to find neighboring solutions.
Genetic algorithms generally use the 2-opt move as a
means of mutating the population.