A hybrid shifting bottleneck-tabu search heuristic for the job shop total weighted tardiness problem

In this paper, we study the job shop scheduling problem with the objective of minimizing the total weighted tardiness. We propose a hybrid shifting bottleneck - tabu search (SB-TS) algorithm by replacing the reoptimization step in the shifting bottleneck (SB) algorithm by a tabu search (TS). In terms of the shifting bottleneck heuristic, the proposed tabu search optimizes the total weighted tardiness for partial schedules in which some machines are currently assumed to have infinite capacity. In the context of tabu search, the shifting bottleneck heuristic features a long-term memory which helps to diversify the local search. We exploit this synergy to develop a state-of-the-art algorithm for the job shop total weighted tardiness problem (JS-TWT). The computational effectiveness of the algorithm is demonstrated on standard benchmark instances from the literature

Flow shop scheduling with earliness, tardiness and intermediate inventory holding costs

We consider the problem of scheduling customer orders in a flow shop with the objective of minimizing the sum of tardiness, earliness (finished goods inventory holding) and intermediate (work-in-process) inventory holding costs. We formulate this problem as an integer program, and based on approximate solutions to two di erent, but closely related, Dantzig-Wolfe reformulations, we develop heuristics to minimize the total cost. We exploit the duality between Dantzig-Wolfe reformulation and Lagrangian relaxation to enhance our heuristics. This combined approach enables us to develop two di erent lower bounds on the optimal integer solution, together with intuitive approaches for obtaining near-optimal feasible integer solutions. To the best of our knowledge, this is the first paper that applies column generation to a scheduling problem with di erent types of strongly NP-hard pricing problems which are solved heuristically. The computational study demonstrates that our algorithms have a significant speed advantage over alternate methods, yield good lower bounds, and generate near-optimal feasible integer solutions for problem instances with many machines and a realistically large number of jobs

A simple, fast, and effective heuristic for the single-machine total weighted tardiness problem

We consider the single-machine total weighted tardiness problem (TWT) where a set of n jobs with general weights w_1,…, w_n, integer processing times p_1,…, p_n, and integer due dates d_1,…, d_n has to be scheduled non-preemptively. If C_j is the completion time of job j then T_j = max(0, C_j - d_j) denotes the tardiness of this job. The objective is to find a schedule S^{*}_{WT} that minimizes the weighted sum of the tardiness costs of all jobs computed as \sum_{j=1}^{n} w_j T_j. This problem is known to be unary NP-hard. Our goal is to design a constructive heuristic for this problem that yields excellent feasible solutions in short computational times by exploiting the structural properties of a preemptive relaxation

A Survey On Multi Trip Vehicle Routing Problem

The vehicle routing problem (VRP) and its variants are well known and greatly explored in the transportation literature. The vehicle routing problem can be considered as the scheduling of vehicles (trucks) to a set of customers under various side constraints. In most studies, a fundamental assumption is that a vehicle dispatched for service finishes its duty in that scheduling period after it returns back to the depot. Clearly, in many cases this assumption may not hold. Thus, in the last decade some studies appeared in the literature where this basic assumption is relaxed, and it is allowed for a vehicle to make multiple trips per period. We consider this new variant of the VRP an important one with direct practical impact. In this survey, we define the vehicle routing problem with multiple trips, define the current state-of-the-art, and report existing results from the current literature

Überlegungen zur Lebenssinnlosigkeit in Kurzgeschichten : "Ist es eine Komödie ist es eine Tragödie?" von Thomas Bernhard und "Die Oper auf der Strasse" von Sabahattin Kudret Aksal

In den letzten Jahren hat es sich durch die Globalisierung bemerkbar gemacht, dass heute die Grenzen zwischen verschiedenen Wissenschaftszweigen sowie Literatur, Kultur und Politik aufgehoben wurden. Die Globalisierung verursachte daher eine unaufhörliche Ausweitung der zwischenmenschlichen Beziehungen. Unter dem Lichte des oben angeführten verdichteten sozialen Beeinflussungsprozesses erreicht der Zeitmensch eine neue d.h. zeitgemäße Wahrnehmungswelt, die zur Globalisierung parallel lief. In diesem Zusammenhang habe ich die inhaltlichen Gemeinsamkeiten der problematischen Seelenzustände in Bezug auf Individualproblematik der betreffenden Texte „Ist Es Eine Komödie Ist Es Eine Tragödie?“ von Th. Bernhard (1931-1989) und „Die Oper Auf Der Strasse“ von S.K. Aksal (1920-1993) in die Hand genommen. Das Ziel des Beitrags ist es, die sinnlosen und problematischen Lebensabschnitte in den oben genannten Kurzgeschichten aus der Sicht des fähigen und talentierten Lesers zustande zu bringen und erst durch die interkulturellen Zusammenhänge die gemeinsamen Menschen- und Zeitfragen durch die kritische Lektüre der Texte dem Leser nahe zu bringen. Meine Arbeitsmethode ist eben deswegen Leserorientierte, psychoanalytische Annäherung und Komparatistik als Untersuchungsform