• Title/Summary/Keyword: Approximation technique

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Proposal of Approximation Analysis Method for GI/G/1 Queueing System

  • Kong, Fangfang;Nakase, Ippei;Arizono, Ikuo;Takemoto, Yasuhiko
    • Industrial Engineering and Management Systems
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    • v.7 no.2
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    • pp.143-149
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    • 2008
  • There have been some approximation analysis methods for a GI/G/1 queueing system. As one of them, an approximation technique for the steady-state probability in the GI/G/1 queueing system based on the iteration numerical calculation has been proposed. As another one, an approximation formula of the average queue length in the GI/G/1 queueing system by using the diffusion approximation or the heuristics extended diffusion approximation has been developed. In this article, an approximation technique in order to analyze the GI/G/1 queueing system is considered and then the formulae of both the steady-state probability and the average queue length in the GI/G/1 queueing system are proposed. Through some numerical examples by the proposed technique, the existing approximation methods, and the Monte Carlo simulation, the effectiveness of the proposed approximation technique is verified.

Integrated Design System using MDO and Approximation Technique (MDO 통합 설계 시스템을 위한 근사기법의 활용)

  • 양영순;박창규;장범선;유원선
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2004.04a
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    • pp.275-283
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    • 2004
  • The paper describes the integrated design system using MDO and approximation technique. In MDO related research, final target is an integrated and automated MDO framework systems. However, in order to construct the integrated design system, the prerequisite condition is how much save computational cost because of iterative process in optimization design and lots of data information in CAD/CAE integration. Therefore, this paper presents that an efficient approximation method, Adaptive Approximation, is a competent strategy via MDO framework systems.

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Polynomially Adjusted Normal Approximation to the Null Distribution of Ansari-Bradley Statistic

  • Ha, Hyung-Tae;Yang, Wan-Youn
    • The Korean Journal of Applied Statistics
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    • v.24 no.6
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    • pp.1161-1168
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    • 2011
  • The approximation for the distribution functions of nonparametric test statistics is a significant step in statistical inference. A rank sum test for dispersions proposed by Ansari and Bradley (1960), which is widely used to distinguish the variation between two populations, has been considered as one of the most popular nonparametric statistics. In this paper, the statistical tables for the distribution of the nonparametric Ansari-Bradley statistic is produced by use of polynomially adjusted normal approximation as a semi parametric density approximation technique. Polynomial adjustment can significantly improve approximation precision from normal approximation. The normal-polynomial density approximation for Ansari-Bradley statistic under finite sample sizes is utilized to provide the statistical table for various combination of its sample sizes. In order to find the optimal degree of polynomial adjustment of the proposed technique, the sum of squared probability mass function(PMF) difference between the exact distribution and its approximant is measured. It was observed that the approximation utilizing only two more moments of Ansari-Bradley statistic (in addition to the first two moments for normal approximation provide) more accurate approximations for various combinations of parameters. For instance, four degree polynomially adjusted normal approximant is about 117 times more accurate than normal approximation with respect to the sum of the squared PMF difference.

Performance Evaluation of a CONWIP System with Compound Poisson Demands and Coxian Processing Times (복합포아송 수요와 Coxian 가공시간을 갖는 CONWIP 시스템의 성능평가)

  • 박찬우;이효성
    • Journal of the Korean Operations Research and Management Science Society
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    • v.31 no.3
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    • pp.63-79
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    • 2006
  • In this study we consider a CONWIP system in which the processing times at each station follow a Coxian distribution and the demands for the finished products arrive according to a compound Poisson process. The demands that are not satisfied immediately are either backordered or lost according to the number of demands that exist at their arrival Instants. For this system we develop an approximation method to calculate performance measures such as steady state probabilities of the number of parts at each station, proportion of lost demands and the mean number of backordered demands. For the analysis of the proposed CONWIP system, we model the CONWIP system as a closed queueing network with a synchronization station and analyze the closed queueing network using a product-form approximation method. A recursive technique is used to solve the subnetwork in the application of the product-form approximation method. To test the accuracy of the approximation method, the results obtained from the approximation method are compared with those obtained by simulation. Comparisons with simulation show that the approximation method provides fairly good results.

Study on an Approximation Technique using MDO (MDO에서 적용가능한 근사기법의 활용에 관한 연구)

  • Park, Chang-Kyu
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.16 no.6
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    • pp.3661-3666
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    • 2015
  • The paper describes the integrated design system using MDO and approximation technique. In MDO related research, final target is an integrated and automated MDO framework systems. However, in order to construct the integrated design system, the prerequisite condition is how much save computational cost because of iterative process in optimization design and lots of data information in CAD/CAE integration. Therefore, this paper presents that an efficient approximation method, Adaptive approximation, is a competent strategy via MDO framework systems.

The Use of Generalized Gamma-Polynomial Approximation for Hazard Functions

  • Ha, Hyung-Tae
    • The Korean Journal of Applied Statistics
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    • v.22 no.6
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    • pp.1345-1353
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    • 2009
  • We introduce a simple methodology, so-called generalized gamma-polynomial approximation, based on moment-matching technique to approximate survival and hazard functions in the context of parametric survival analysis. We use the generalized gamma-polynomial approximation to approximate the density and distribution functions of convolutions and finite mixtures of random variables, from which the approximated survival and hazard functions are obtained. This technique provides very accurate approximation to the target functions, in addition to their being computationally efficient and easy to implement. In addition, the generalized gamma-polynomial approximations are very stable in middle range of the target distributions, whereas saddlepoint approximations are often unstable in a neighborhood of the mean.

A Rigorous 2D Approximation Technique for 3D Waveguide Structures for BPM Calculations

  • Han, Young-Tak;Shin, Jung-Uk;Kim, Duk-Jun;Park, Sang-Ho;Park, Yoon-Jung;Sung, Hee-Kyung
    • ETRI Journal
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    • v.25 no.6
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    • pp.535-537
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    • 2003
  • We propose a rigorous 2D approximation technique for the 3D waveguide structures; it can minimize the well-known approximation errors of the commonly used effective index method. The main concept of the proposed technique is to compensate for the effective cladding index in the equivalent slab model of the original channel waveguide from the modal effective index calculated by the nonuniform 2D finite difference method. With simulations, we used the proposed technique to calculate the coupling characteristics of a directional coupler by the 2D beam propagation method, and the results were almost exactly the same as the results calculated by the 3D beam propagation method.

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An Approximation of Gaussian Pyramid Top Layer for Simplification of Image Pyramid-based Multi Scale Exposure Fusion Algorithm (이미지 피라미드 기반의 다중 노출 영상 융합기법 단순화를 위한 가우시안 피라미드 최상층 근사화)

  • Hwang, Tae Hun;Kim, Jin Heon
    • Journal of Korea Multimedia Society
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    • v.22 no.10
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    • pp.1160-1167
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    • 2019
  • Because of the dynamic range limitation of digital equipment, it is impossible to obtain dark and bright areas at the same time with one shot. In order to solve this problem, an exposure fusion technique for fusing a plurality of images photographed at different exposure amounts into one is being studied. Among them, Laplacian pyramid decomposition based fusion method can generate natural HDR image by fusing images of various scales. But this requires a lot of computation time. Therefore, in this paper, we propose an approximation technique that achieves similar performance and greatly shortens computation time. The concept of vanishing point image for approximation is introduced, and the validity of the proposed approach is verified by comparing the computation time with the resultant image.

An Error-Bounded B-spline Fitting Technique to Approximate Unorganized Data (무작위 데이터 근사화를 위한 유계오차 B-스플라인 근사법)

  • Park, Sang-Kun
    • Korean Journal of Computational Design and Engineering
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    • v.17 no.4
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    • pp.282-293
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    • 2012
  • This paper presents an error-bounded B-spline fitting technique to approximate unorganized data within a prescribed error tolerance. The proposed approach includes two main steps: leastsquares minimization and error-bounded approximation. A B-spline hypervolume is first described as a data representation model, which includes its mathematical definition and the data structure for implementation. Then we present the least-squares minimization technique for the generation of an approximate B-spline model from the given data set, which provides a unique solution to the problem: overdetermined, underdetermined, or ill-conditioned problem. We also explain an algorithm for the error-bounded approximation which recursively refines the initial base model obtained from the least-squares minimization until the Euclidean distance between the model and the given data is within the given error tolerance. The proposed approach is demonstrated with some examples to show its usefulness and a good possibility for various applications.

Optimization of Steel Box Girder Bridges using Approximate Reanalysis Technique (재해석 기법을 이용한 강상자형교의 최적설계)

  • Min, Dae-Hong;Yoon, Woo-Hyun;Chung, Jee-Seung;Yang, Sung-Don
    • Journal of the Korean Society of Safety
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    • v.26 no.4
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    • pp.80-86
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    • 2011
  • Structural optimization algorithm of steel box girder bridges using improved higher-order approximate reanalysis technique is proposed in this paper. The proposed approximation method is a generalization of the convex approximation method. The order of the approximate reanalysis for each function is analytically adjusted in the optimization process. This self-adjusted capability makes the approximate structural analysis values conservative enough to maintain the optimum design point of the approximate problem. The efficiency of proposed optimazation algorithm, compared with conventional algorithm, is successfully demonstrated in the steel box girder bridges. The efficiency and robustness of proposed algorithm is also demonstrated in practical steel box girder bridges.