“…There have been other improvements on the running time for the all-pairs shortest paths problem for some special case graphs [2,10,15,16,17,18,19,22,26], but they all have worst-case time O(nE). Karger, Koller, and Phillips [19] show that Ω(nE) is a lower bound for directed graphs on the running time of any algorithm which is "pathcomparison based," which is evidence that it is hard to improve exact algorithms with this approach.…”