This method will return an approximate minimal traveling salesman tour (hamiltonian cycle).
This algorithm requires that the graph be complete and the triangle inequality exists (if
x,y,z are vertices then d(x,y)+d(y,z) < d(x,z) for all x,y,z) then this algorithm will
guarantee a hamiltonian cycle such that the total weight of the cycle is less than or equal
to double the total weight of the optimal hamiltonian cycle. The optimal solution is
NP-complete, so this is a decent approximation that runs in polynomial time.