Ant algorithms (also known as Ant Colony Optimization) are a class of
metaheuristic search algorithms that have been successfully applied to solving NP
hard problems . Ant algorithms are biologically inspired from the behaviour of
colonies of real ants, and in particular how they forage for food. One of the main ideas
behind this approach is that the ants can communicate with one another through
indirect means (stigmergy) by making modifications to the concentration of highly
volatile chemicals called pheromones in their immediate environment.
The Traveling Salesman Problem (TSP) is an NP complete problem addressed by the
optimization community having been the target of considerable research . The TSP is
recognized as an easily understood, hard optimization problem of finding the shortest
circuit of a set of cities starting from one city, visiting each other city exactly once,
and returning to the start city again. The TSP is often used to test new, promising
optimization heuristics. Formally, the TSP is the problem of finding the shortest
Hamiltonian circuit of a set of nodes. There are two classes of TSP problem:
symmetric TSP, and asymmetric TSP (ATSP). The difference between the two classes
is that with symmetric TSP the distance between two cities is the same regardless of
the direction you travel; with ATSP this is not necessarily the case.
Ant Colony Optimization has been successfully applied to both classes of TSP with
good, and often excellent, results. The ACO algorithm skeleton for TSP is as follows :