Many aspiration criteria have been proposed for TS, and the following describes those being tested in this work. The most naïve option is simply to exclude aspiration; if a move is tabu it will not be allowed, even if there could be ways of detecting that it would lead to a previously unvisited solution. This option will be labeled as NO (no aspiration). This appears to be perhaps the second most commonly used aspiration criterion, although as already noted in (Glover, 1986) other alternatives have produced solutions of better quality.
The aspiration criterion that seems to be most commonly used will be labeled as NB (new best aspiration). It was described in (Glover, 1986) and appears both simple and reasonable: the tabu status of a move can be revoked whenever the move leads to a solution that is better than any solution recorded during the search so far.