Scheduling with Time Lags

Scheduling is essential when activities need to be allocated to scarce resources over time. Motivated by the problem of scheduling barges along container terminals in the Port of Rotterdam, this thesis designs and analyzes algorithms for various on-line and off-line scheduling problems with time lags. A time lag specifies a minimum time delay required between the execution of two consecutive operations of the same job. Time lags may be the result of transportation delays (like the time required for barges to sail from one terminal to the next), the duration of activities that do not require resources (like drying or cooling down), or intermediate processes on non-bottleneck machines between two bottleneck machines. For the on-line flow shop, job shop and open shop problems of minimizing the makespan, we analyze the competitive ratio of a class of greedy algorithms. For the off-line parallel flow shop scheduling problem with time lags of minimizing the makespan, we design algorithms with fixed worst-case performance guarantees. For two special subsets of scheduling problems with time lags, we show that Polynomial-Time Approximation Schemes (PTAS) can be constructed under certain mild conditions. For the fixed interval scheduling problem, we show that the flow shop problem is solvable in polynomial time in the case of equal time lags but that it is NP-hard in the strong sense for general time lags. The fixed interval two-machine job shop and open shop problems are shown to be solvable in polynomial time if the time lags are smaller than the processing time of any operation

On-line scheduling of small open shops

Includes bibliographical referencesAvailable from British Library Document Supply Centre- DSC:9261. 954(306) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

On-line scheduling of small open shops

Includes bibliographical referencesAvailable from British Library Document Supply Centre- DSC:9261. 954(306) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

On-line scheduling of small open shops

We investigate theprobl4 ofon-l.E schedulw4 open shops of two and three machines with an objective of minimizing theschedul makespan. We #rst propose a 1.848-competitive permutationalmutati for the non-preemptiveschedulmp problu of two machines and show that no permutationalrmutat can be better than 1.754-competitive.Secondlo wedevel. a (27=19)-competitiveal)-comp for the preemptive schedulve problu of three machines, which is most competitive. ? 2001El1C8.7 Science B.V.Al rights reserved

On-line scheduling of small open shops

We investigate the problem of on-line scheduling open shops of two and three machines with an objective of minimizing the schedule makespan. We first propose a 1.848-competitive permutation algorithm for the non-preemptive scheduling problem of two machines and show that no permutation algorithm can be better than 1.754-competitive. Secondly, we develop a (27/19)-competitive algorithm for the preemptive scheduling problem of three machines, which is most competitive. (C) 2001 Elsevier Science B.V. All rights reserved