A more general algorithm for computing closed semiring costs between vertices of a directed graph

Abstract

This note describes a generalization of an algorithm given by Aho, Hopcroft, and Ullman [1], originally derived from the work of Kleene [2] and McNaughton and Yamada [3]. The algorithm is used to compute the total cost of all paths between each pair of vertices in a directed graph when the cost of each edge is known. The cost of a path is defined as the product of the costs of the edges forming it, and the total cost of a set of paths is the sum of their individual costs. If there are n vertices labeled 1 through n and E [ i, j ] is the cost of the edge from vertex i to vertex j (or is zero when there is no such edge), then the total cost T [ i, j ] of all paths from i to j is the solution of the equation T [ i, j ] = δ[ i, j ] + ∑ n k -1 E [ i, k ]· T [ k, j ], (1) where δ[ i, i ] = 1 (the cost of the path of no edges from i to i ) and δ[ i, j ] = 0 if i ≠ j . To assure that T [ i, j ] is always well-defined, costs are required to be elements from an algebraic structure called a closed semiring.