Two machine openshop scheduling with machine-dependent processing times

In a recent paper, Dror (1992) presented several results for openshop scheduling with machine dependent processing times. In this note, we present clarifications regarding the algorithm developed by him for minimizing the sum of job completion times (or average flow time) in a 2 machine openshop and show that it is not optimal for all cases. Finally, we present an optimal algorithm for the same 2 machine openshop problem.