We study due-date assignment problems with common flow allowance on a proportionate flowshop. We focus on both minsum and minmax objectives. Both cases are extended to a setting of a due-window. The proposed solution procedures are shown to be significantly different from those of the single machine problems. All the problems studied here are solved in polynomial time: the minsum problems in O(n 2) and the minmax problems in O(nlog n), where n is the number of jobs. 
Minsum and minmax scheduling on a proportionate flowshop with common flow-allowance