Labeled Shortest Paths

This paper gives a shortest path algorithm for CFG (context free grammar) labeled and weighted digraphs where edge weights may be positive or negative, but negative-weight cycles are not allowed in the underlying unlabled graph. These results build directly on an algorithm of Barrett, Jacob, and Marathe [1]. In addition to many other results, they gave a shortest path algorithm for CFG labeled and weighted digraphs where all edges are nonnegative. Our algorithm is based closely on Barrett, et al.’s algorithm as well as Johnson’s algorithm for shortest paths in digraphs whose edges may have positive or negative weights.