CowboyRobot writes: "Clay Breshears at Dr. Dobb's has a fun formula for optimizing the drive between multiple cities. "Think of a map as an instance of a graph, the cities are the nodes and the roads between cities are the edges. The length of the road is the weight of the corresponding edge. The All-Pairs Shortest Path problem takes a graph of n nodes represented by an n x n weight matrix, W. The result is an n x n matrix, D (for distance), where the D[i][j] entry holds the minimum weight of the path from node i to node j. Entries in the W matrix can be zero, positive (if a direct edge lies between the two nodes), or the infinity value where there is no direct edge between the nodes.""