Minimizing total completion time with linear deterioration: A new lower bound

We study scheduling problems in which the job processing times are linearly deteriorating. Each job has a constant (job-independent) basic processing time and a job-dependent deterioration rate. The objective function is minimum total completion time. The machine settings considered are: single machine and parallel identical machines. The complexity status of these problems has been an open question for the last three decades. We introduce a new lower bound on the optimal total completion time, which is shown numerically (through a comparison to the results obtained by a simple heuristic) to be extremely accurate for both problems.