2.The following basic speedup modification is widely used in practical implementations of BF. It groups Relax(u, v) executions to bunches with the same vertex u, called “scanning u”. When scanning u, it stores the value of d(u). At each round of BF, not all vertices are scanned. Scanning of vertex u is skipped if its current d value equals its d value stored at the last time (in such a case, scanning u is useless). Although the worst case bound of this modification is the same as that of the basic BF, it is known that in practice, this modification significantly decreases the running time.