 Thus, the name may be somewhat misleading.It results from the origin of voltage graphs as dual to the current graphs of topological graph theory.The derived graph of a voltage graph formula_4 is the graph formula_5 whose vertex set is formula_6 and whose edge set is formula_7, where the endpoints of an edge ("e", "k") such that "e" has tail "v" and head "w" are formula_8 and formula_9.