A polynomial algorithm for special case of the one-machine scheduling problem with time-lags

The standard one-machine scheduling problem consists in scheduling a set of jobs in one machine which can handle only one job at a time, minimizing the maximum lateness. Each job is available for processing at its release date, requires a known processing time and after finishing the processing, it is delivery after a certain time. There also can exists precedence constraints between pairs of jobs, requiring that the first jobs must be completed before the second job can start. An extension of this problem consists in assigning a time interval between the processing of the jobs associated with the precedence constrains, known by finish-start time-lags. In presence of this constraints, the problem is NP-hard even if preemption is allowed. In this work, we consider a special case of the one-machine preemption scheduling problem with time- lags, where the time-lags have a chain form, and propose a polynomial algorithm to solve it. The algorithm consist in a polynomial number of calls of the preemption version of the Longest Tail Heuristic. One of the applicability of the method is to obtain lower bounds for NP-hard one-machine and job-shop scheduling problems. We present some computational results of this application, followed by some conclusions.One-machine scheduling, polynomial algorithms, lower bounds

Complexity Results for Single-Machine Problems with Positive Finish-Start Time-Lags

In a single-machine problem with time-lags a set of jobs has to be processed on a single machine in such a way that certain timing restrictions between the finishing and starting times of the jobs are satisfied and a given objective function is minimized. We consider the case of positive finishstart time-lags l ij which mean that between the finishing time of job i and the starting time of job j the minimal distance l ij has to be respected. New complexity results are derived for single-machine problems with constant positive time-lags l ij = l which also lead to new results for flow-shop problems with unit processing times and job precedences. Key words: complexity results, time-lags, single machine, flow-shop problem Supported by the Deutsche Forschungsgemeinschaft, Project `Komplexe Maschinen-Schedulingprobleme ' 1 Introduction In a single-machine problem a set of jobs j = 1; : : : ; n has to be processed without preemption on a single machine in such a way that at most one jo..

Flow shop scheduling with two machines

A flow shop problem has n jobs (i = 1.. , n) on m machines (j = 1, . . . , m) and a job consists two operations and the jth operation of each job must be processed on machine j. Any job can start only on machine j if it is completed on machine j-1 and if machine j is free. Each operation has a known processing time pij. The work here focuses on the case m = 2 where the objective is to minimize (1) the makespan (Cmax) and (2) the average completion time (sumCi); We first review an efficient greedy algorithm by Johnson for Cmax and give detailed proofs; The we note that in the case of sumCi the problem is harder, in fact it is NP-hard. To tackle this problem we have implemented a branch and bound algorithm to find the optimal schedules in some cases. We also constructed a genetic algorithm under MIT\u27s GALib C++ package. Solutions from the branch and bound algorithm are used as benchmarks for the solutions found by the genetic algorithm

Permutation flow shops with exact time lags to minimise maximum lateness

International audienceIn this paper we investigate the m-machine permutation flow shop scheduling problem where exact time lags are defined between consecutive operations of every job. This generic model can be used for the study and analysis of various real situations that may arise, for instance, in the food-producing, pharmaceutical and steel industries. The objective is to minimise the maximum lateness. We study polynomial special cases and provide a dominance relation. We derive lower and upper bounds that are integrated in a branch-and-bound procedure to solve the problem. Three branching schemes are proposed and compared. We perform a computational analysis to evaluate the efficiency of the developed method

Ensuring Service Level Agreements for Composite Services by Means of Request Scheduling

Building distributed systems according to the Service-Oriented Architecture (SOA) allows simplifying the integration process, reducing development costs and increasing scalability, interoperability and openness. SOA endorses the reusability of existing services and aggregating them into new service layers for future recycling. At the same time, the complexity of large service-oriented systems negatively reflects on their behavior in terms of the exhibited Quality of Service. To address this problem this thesis focuses on using request scheduling for meeting Service Level Agreements (SLAs). The special focus is given to composite services specified by means of workflow languages. The proposed solution suggests using two level scheduling: global and local. The global policies assign the response time requirements for component service invocations. The local scheduling policies are responsible for performing request scheduling in order to meet these requirements. The proposed scheduling approach can be deployed without altering the code of the scheduled services, does not require a central point of control and is platform independent. The experiments, conducted using a simulation, were used to study the effectiveness and the feasibility of the proposed scheduling schemes in respect to various deployment requirements. The validity of the simulation was confirmed by comparing its results to the results obtained in experiments with a real-world service. The proposed approach was shown to work well under different traffic conditions and with different types of SLAs

Algorithmes exacts et approchés pour des problèmes d'ordonnancement et de placement

Dans cette thèse, nous nous intéressons à la résolution de quelques problèmes d'optimisation combinatoires que nous avons choisi de traiter en deux volets. Dans un premier temps, nous étudions des problèmes d'optimisation issus de l'ordonnancement d'un ensemble de tâches sur des machines de calcul et où on cherche à minimiser l'énergie totale consommée par ces machines tout en préservant une qualité de service acceptable. Dans un deuxième temps, nous traitons deux problèmes d'optimisation classiques à savoir un problème d'ordonnancement dans une architecture de machines parallèles avec des temps de communication, et un problème de placement de données dans des graphes modélisant des réseaux pair-à-pair et visant à minimiser le coût total d'accès aux données.In this thesis, we focus on solving some combinatorial optimization problems that we have chosen to study in two parts. Firstly, we study optimization problems issued from scheduling a set of tasks on computing machines where we seek to minimize the total energy consumed by these machines while maintaining acceptable quality of service. In a second step, we discuss two optimization problems, namely a classical scheduling problem in architecture of parallel machines with communication delays, and a problem of placing data in graphs that represent peer-to-peer networks and the goal is to minimize the total cost of data access.EVRY-Bib. électronique (912289901) / SudocSudocFranceF