No-wait flowshop scheduling is as hard as asymmetric traveling salesman problem

In this paper we study the classical no-wait flowshop scheduling problem with makespan objective (F|no − wait|C max in the standard three-field notation). This problem is well-known to be a special case of the asymmetric traveling salesman problem (ATSP) and as such has an approximation algorithm with logarithmic performance guarantee. In this work we show a reverse connection, we show that any polynomial time α-approximation algorithm for the no-wait flowshop scheduling problem with makespan objective implies the existence of a polynomial-time α(1 + ε)-approximation algorithm for the ATSP, for any ε > 0. This in turn implies that all non-approximability results for the ATSP (current or future) will carry over to its special case. In particular, it follows that no-wait flowshop problem is APX-hard, which is the first non-approximability result for this problem