This is a heuristic search algorithm for finding the MP tree, and is somewhat similar to the branch-and bound search method. However, in this algorithm, many trees that are unlikely to have a small local tree length are eliminated from the computation of their L values. Thus while the algorithm speeds up the search for the MP tree, as compared to the branch-and-bound search, the final tree or trees may not be the true MP tree(s). The user can specify a search factor to control the extensiveness of the search and MEGA adds the user specified search factor to the current local upper bound. Of course, the larger the search factor, the slower the search, since many more trees will be examined.
(See also Nei & Kumar (2000), pages 122, 125)