Bellman-Ford algorithm

For now, see http://en.wikipedia.org/wiki/Bellman-Ford_algorithm BEGIN FOR ALL V=!S,D[V]=~; D[S]=0; FOR ALL V, X[V]=NIL; FOR STEP =1 TO N;     FOR(U,V) BELONGS TO E;        IF (D[W]+W[U,V]< D[V]) D[V] =D[W]+W[U,V]<D[V]);          X[V]=U; END;