排序方式: 共有11条查询结果,搜索用时 15 毫秒
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Cloud computing enables a conventional relational database system's hardware to be adjusted dynamically according to query workload, performance and deadline constraints. One can rent a large amount of resources for a short duration in order to run complex queries efficiently on large-scale data with virtual machine clusters. Complex queries usually contain common subexpressions, either in a single query or among multiple queries that are submitted as a batch. The common subexpressions scan the same relations, compute the same tasks (join, sort, etc.), and/or ship the same data among virtual computers. The total time spent for the queries can be reduced by executing these common tasks only once. In this study, we build and use efficient sets of query execution plans to reduce the total execution time. This is an NP-Hard problem therefore, a set of robust heuristic algorithms, Branch-and-Bound, Genetic, Hill Climbing, and Hybrid Genetic-Hill Climbing, are proposed to find (near-) optimal query execution plans and maximize the benefits. The optimization time of each algorithm for identifying the query execution plans and the quality of these plans are analyzed by extensive experiments. 相似文献
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基于离散系数滤波器设计问题已有的半定规划松弛模型,利用文献[6]的方法给出了该问题的二次规划松弛模型,该模型能给出比半定规划模型更好的界,然后运用分支定界方法求解该模型。与随机扰动方法相比,该方法能得到一个性能更好的次优解,对于精度要求较高的滤波器设计问题,这种方法非常有效,并通过了仿真实验的证实。 相似文献
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Many real-world systems (such as cellular telephones, transportation, etc.) are multistate-node acyclic network (MNAN) composed of multistate-nodes. Such network has a source node (position) where the signal source is located, a number of sink nodes that only receive the signal, and a number of intermediate nodes that retransmit the received signal to some other nodes. The non-sink node has different states determined by a set of nodes receiving the signal directly from it. The reliability of MNAN can be computed in terms of minimal trees (MTs). Based on the Branch-and-Bound algorithm, we developed an intuitive algorithm that is simpler than the best-known existing method. The computational complexity of the proposed algorithm is also analyzed. One example is illustrated to show how all MTs are generated by the proposed algorithm. The reliability of this example is then computed. 相似文献
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Zusammenfassung Es wird ein Verfahren zur kostenminimalen Festlegung einer kapazitätsorientierten Jahresarbeitszeitverteilung für den Produktionsbereich vorgestellt. Dazu wird auf Basis einer vorgegebenen Menge von Schichtplänen eine simultane Auswahl- und Reihenfolgeplanung durchgeführt, die die Jahresarbeitszeitverteilung optimiert. Im Gegensatz zu den gängigen Verfahren zur Jahresarbeitszeitplanung können bei dieser Vorgehensweise die durch die Schichtpläne auferlegten Arbeitszeitrestriktionen sowie die damit verbundenen Kosten im Detail berücksichtigt werden. Der Einfluß planungsrelevanter Parameter auf die resultierende Jahresarbeitszeitverteilung wird ausführlich diskutiert. 相似文献
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Flow shop scheduling for separation model of set-up and net process based on Branch-and-Bound method
Kenzo Kurihara Yann-Liang Li Nobuyuki Nishiuchi Kazuaki Masuda 《Computers & Industrial Engineering》2009,57(2):550
Lots of research reports on flow shop scheduling problems have been reported. Generally speaking, these models are applicable to a simple model with no separation of set-up processes and net ones. In many production lines, we cannot ignore the set-up times in comparison with the net processing times. We can expect to shorten the total processing time by executing the set-up processes and net ones in parallel. We need a parallel operation model to improve schedule results.We will propose a new scheduling method for multi-stage flow shops. The aim of the method is to shorten the total processing time by operating the set-up processes and the net ones of each job in parallel. We applied the Branch-and-Bound method and developed a new calculation algorithm for the lower bound estimation of the total processing time. Finally, we will evaluate our proposed method by some numerical experiments using actual production line data. 相似文献
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The cutwidth minimization problem consists of finding a linear arrangement of the vertices of a graph where the maximum number of cuts between the edges of the graph and a line separating consecutive vertices is minimized. We first review previous approaches for special classes of graphs, followed by lower bounds and then a linear integer formulation for the general problem. We then propose a branch-and-bound algorithm based on different lower bounds on the cutwidth of partial solutions. Additionally, we introduce a Greedy Randomized Adaptive Search Procedure (GRASP) heuristic to obtain good initial solutions. The combination of the branch-and-bound and GRASP methods results in optimal solutions or a reduced relative gap (difference between upper and lower bounds) on the instances tested. Empirical results with a collection of previously reported instances indicate that the proposed algorithm is able to solve all the small instances (up to 32 vertices) as well as some of the large instances tested (up to 158 vertices) using less than 30 minutes of CPU time. We compare the results of our method with previous lower bounds, and with the best previous linear integer formulation solved using Cplex. Both comparisons favor the proposed procedure. 相似文献
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Alexandre Dolgui Anton V. Eremeev Viatcheslav S. Sigaev 《Journal of Intelligent Manufacturing》2007,18(3):411-420
In this paper, we consider the problem of buffer space allocation for a tandem production line with unreliable machines. This problem has various formulations all aiming to answer the question: how much buffer storage to allocate between the processing stations? Many authors use the knapsack-type formulation of this problem. We investigate the problem with a broader statement. The criterion depends on the average steady-state production rate of the line and the buffer equipment acquisition cost. We evaluate black-box complexity of this problem and propose a hybrid optimization algorithm (HBBA), combining the genetic and branch-and-bound approaches. HBBA is excellent in computational time. HBBA uses a Markov model aggregation technique for goal function evaluation. Nevertheless, HBBA is more general and can be used with other production rate evaluation techniques. 相似文献
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Leo Liberti Sergei Kucherenko 《International Transactions in Operational Research》2005,12(3):263-285
In this paper, we compare two different approaches to nonconvex global optimization. The first one is a deterministic spatial Branch‐and‐Bound algorithm, whereas the second approach is a Quasi Monte Carlo (QMC) variant of a stochastic multi level single linkage (MLSL) algorithm. Both algorithms apply to problems in a very general form and are not dependent on problem structure. The test suite we chose is fairly extensive in scope, in that it includes constrained and unconstrained problems, continuous and mixed‐integer problems. The conclusion of the tests is that in general the QMC variant of the MLSL algorithm is generally faster, although in some instances the Branch‐and‐Bound algorithm outperforms it. 相似文献