Vectorized Floyd-Warshall

Vectorized (fast) implementation of the Floyd-Warshall all pairs shortest path algorithm.

The Floyd-Warshall algorithm computes the all pairs shortest path matrix for a given adjacency matrix. The algorithm is O(n^3), and in most implementations you will see 3 nested for loops. This is very inefficient in Matlab, so in this version the two inner loops are vectorized (and as a result, it runs much faster).

Make sure that your input matrix is initialized properly -- A(i,j) = Inf if i and j are not neighbors.