摘要:

AbstractIn this Blackett Lecture, Professor Littlechild, Director General of Electricity Supply in the UK's Office of Electricity Regulation, renews acquaintance with some models he has developed over the years, introduces some models he has recently met, and discusses models that it would seem to be worthwhile developing. He concludes that for all concerned in the electricity industry, success depends on ever improving decision-making, in which OR has a vital role.

ISSN:0160-5682    

DOI:10.1057/jors.1996.73

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractRecently a public committee has been appointed by the Israeli government. The committee was assigned to prepare regional plans for the northeastern Negev, in the southern part of Israel, in order to absorb some of the large waves of immigrants (about 400,000) expected by the year 2000. Among the strategic issues treated by the committee were the questions when, where and whether to build a new hospital in the area. The locational decision was studied by first identifying a finite candidate set of possible sites. At the final stage various quantitative locational models were employed. In the next stage a subjective multicriteria model was further used to derive locationally preferred solutions. This paper focuses on the first stage. Furthermore, the suggested solution approach is discussed in light of strategic issues.

ISSN:0160-5682    

DOI:10.1057/jors.1996.74

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractWhen a job is processed in a hypercube multi-processor, it is allocated a cube of processing elements of the requisite size. There are three distinct costs involved in the hypercube scheduling problem: the cost of detecting a free cube (allocation), the cost of migrating jobs and merging the free spaces to accommodate a larger cube request (relocation) and the cost of not meeting the due date (tardiness). Traditionally, research in this area has focused on finding efficient algorithms for allocating a free cube (if any) in the hypercube system. The relocation cost has been treated as an independent cost metric. The role of scheduling has not received much attention and present subcube allocation methods assume a first-come-first-serve (FCFS) approach over the input job set.This paper considers the underlying scheduling issues in a hypercube processing system and shows how techniques other than FCFS scheduling of the incoming jobs can help in reducing the relocation cost and hence the overall subcube resource assignment cost. We discuss five simple and easily implementable dispatching heuristics, and compare their relative performance with the FCFS scheduling rule to demonstrate the advantages of scheduling in subcube allocation.

ISSN:0160-5682    

DOI:10.1057/jors.1996.75

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThis paper deals with approximate analysis methods for open queueing networks. External and internal flows from and to the nodes are characterized by renewal processes with discrete time distributions of their interarrival times. Stationary distributions of the waiting time, the queue size and the interdeparture times are obtained using efficient discrete time algorithms for single server (GI/G/1) and multi-server (GI/D/c) nodes with deterministic service. The network analysis is extended to semi-Markovian representations of each flow among the nodes, which include parameters of the autocorrelation function.

ISSN:0160-5682    

DOI:10.1057/jors.1996.76

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractWe contrast the different approaches of Data Envelopment Analysis (DEA) and Multiple Criteria Decision Making (MCDM) to superficially similar problems. The concepts of efficiency and Pareto optimality in DEA and MCDM are compared, and a link is demonstrated between the ratio efficiency definition in DEA and a distance measure in input–output space based on linear value functions. The problem of weight sensitivity is discussed in terms of value measurement theory, highlighting the assumptions needed during model formulation in order to justify the use of value judgements to constrain weight flexibility in DEA. Finally, we propose a stochastic approach, in which a probability distribution on efficiencies can be derived for each decision making unit, as a basis for comparison.

ISSN:0160-5682    

DOI:10.1057/jors.1996.77

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractWe examine the effects of different machine criticality measures (MCMs) and subproblem solution procedures (SSPs) on the performance of Shifting Bottleneck (SB) methods for the problem of minimizing maximum lateness in a job shop. Extensive computational experiments show that for problems with balanced workloads and random routeings simple MCMs and SSPs can be used without affecting solution quality. Routeing structure affects the performance of the SB method significantly. We also find that, contrary to some previous studies, the problem of maintaining feasibility in the SB method is significant.

ISSN:0160-5682    

DOI:10.1057/jors.1996.78

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractWe develop a search procedure for project scheduling problems with multiple resource constraints as well as precedence constraints. The procedure is applied to three popular search heuristics, simulated annealing, tabu search and genetic algorithms. In the heuristics, a solution is represented with a string of numbers each of which denotes priority of each activity. The priorities are used to select an activity for scheduling among competing ones. The search heuristics with this encoding method can always generate feasible neighbourhood solutions for a given solution. Moreover, this encoding method is very flexible in that problems with objective functions of a general functional form (such as a nonlinear function) and complex constraints can be considered without much difficulty. Results of computational tests on the performance of the search heuristics showed that the search heuristics, especially the simulated annealing and tabu search algorithms worked better than existing heuristics.

ISSN:0160-5682    

DOI:10.1057/jors.1996.79

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThis study is concerned with minimizing the total discounted cost of operating an inventory system and providing the warehouse space necessary to accommodate the replenishment lots, under the assumption of constant product demand. The use of an approximation objective function for the single-item case allows the optimal warehouse size as well as the ratio of relevant investment costs to relevant inventory costs to be written in closed-form. Based upon the value of this ratio, circumstances are identified under which an integrated approach is justified, and others under which the inventory policy and storage capacity can be determined sequentially. The multi-item version of the problem under study is solved by the Lagrangian multiplier method, given that no coordination takes place between the items. Finding the optimal Lagrange multiplier can be accomplished efficiently by the Newton–Raphson method.

ISSN:0160-5682    

DOI:10.1057/jors.1996.80

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe paper presents an application oriented procedure for solving the project management duration/resource tradeoff problem. A procedure is presented for reducing a project from a normal to a crash duration state at a minimum amount of additional resource expenditure assuming a linear utilization functions. The procedure is network based using a graphical Cut Search Approach to locate the minimal resource level at each reduction in total project duration. Activity-on-arc networks and flow networks are utilized. The paper is presented for practical application and for conceptual development as compared to a theoretical treatment.

ISSN:0160-5682    

DOI:10.1057/jors.1996.81

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractIn this paper, the set covering problem (SCP) is considered. Several algorithms have been suggested in the literature for solving it. We propose a new algorithm for solving the SCP which is based on the genetic technique. This algorithm has been implemented and tested on various standard and randomly generated test problems. Preliminary results are encouraging, and are better than the existing heuristics for the problem.

ISSN:0160-5682    

DOI:10.1057/jors.1996.82

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor