The first is a heuristic technique, defined in accordance to the Ant System metaphor, and includes as a distinctive feature the use of a new lower bound at each constructive step. The second is a branch and bound exact approach, containing some elements introduced in the Ant algorithm.
Computational results prove the effectiveness of both approaches.
98-1, Computer Science, Univ. of Bologna. 98-1, Computer Science, Univ. of Bologna. Doc 74 Distributed Optimization by Ant Colonies - Colorni, Dorigo et al. The Ant System Applied to the Quadratic Assignment Problem - Maniezzo, Colorni et al. Resende, Ramakrishnan et al.