• 한국통신학회논문지
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• 제31권3A호
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• pp.249-253
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• 2006

본 논문에서는 CDMA2000 역방향 링크에서 DS/CDMA 용 rake structure antenna away에 적용되는 새로운 방식의 simplex downhill 최적화 기법 빔포밍 알고리즘을 제안하고 있다. 본 논문에서 제안한 방법은 요구되는 신호(파일럿) 분산 행렬과 간섭 분산 행렬을 사용하고 있으며, 빔포밍 가중치들은 simplex downhill 최적화 알고리즘을 사용하여 최대 SINR 기준에 따라 만들어 졌다. 본 논문에서 제안한 구조는 기존의 적응 빔포밍 알고리즘보다 더 적은 계산량, 개선된 수렴 속도와 성능을 제공한다. Simplex downhill 방법은 최적화되기 위한 결정함수의 값만을 요구하기 때문에 최적화되거나 준최적화된 가중치 벡터를 찾기에 적합한 방식이다. 또한 rake beamformer 성능을 공간 채널모델에서의 여러종류 파라미터 값에 대하여 분석하였으며, 기존 방식의 rake 수신기와 제안된 방식을 동일한 수신 전력에서 비교 분석하였다.

• 한국수자원학회논문집
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• 제35권5호
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• pp.541-552
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• 2002

본 연구에서는 전체탐색기법 중 Simplex법의 원리를 이용한 SCE-UA법과 Annealing-Simplex (A-S)법을 일유출량 추정 수문모형인 탱크모형의 매개변수 보정에 적용하여 국부탐색기법인 Downhill Simplex법의 결과와 비교하여 탐색능력을 평가하였다. 오차가 없는 합성자료를 사용한 보정에서 A-S법이 목적함수에 관계없이 전역최적해를 탐색하는 결과를 나타냈으며, SCE-UA법은 ABSERR를 목적함수로 사용할 경우에 전역최적해를 탐색하는 결과를 나타냈으며, 다른 목적함수를 사용하는 경우에는 최적해에 가까운 탐색결과를 나타냈다. Downhill Simplex법은 초기값에 따라 다근 탐색결과를 나타냈으며, 최적해에 가까운 초기값을 사용할 경우 전역 최적해를 탐색하는 결과를 나타냈다. 실측자료를 사용한 보정에서는 A-S법과 SCE-UA법이 목적함수에 관계없이 양호한 결과를 나타냈다. 두 개의 서로 다른 단일 목적함수를 조합하여 만든 목적함수 중 DRMS와 NS의 조합에 의해 만들어진 목적함수인 DN이 다른 목적함수보다 저유량에 비중을 더 둔 예측결과를 나타냈으며, 전체 자료기간에 대해서 양호한 예측결과론 나타냈다.

• 한국농공학회지
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• 제44권7호
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• pp.1-13
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• 2002

Two global optimization methods, the SCE-UA method and the Annealing-simplex (A-S) method for calibrating a daily rainfall-runoff model, a Tank model, was compared with that of the Downhill Simplex method. The performance of the four objective functions, DRMS (daily root mean square), HMLE (heteroscedastic maximum likelihood estimator), ABSERR (mean absolute error), and NS (Nash-Sutcliffe measure), was tested and synthetic data and historical data were used. In synthetic data study. 100% success rates for all objective functions were obtained from the A-S method, and the SCE-UA method was also consistently able to obtain good estimates. The downhill simplex method was unable to escape from local optimum, the worst among the methods, and converged to the true values only when the initial guess was close to the true values. In the historical data study, the A-S method and the SCE-UA method showed consistently good results regardless of objective function. An objective function was developed with combination of DRMS and NS, which putted more weight on the low flows.

• ETRI Journal
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• 제36권3호
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• pp.439-449
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• 2014

In this paper, a novel vision-based nighttime vehicle detection approach is presented, combining state machines and downhill simplex optimization. In the proposed approach, vehicle detection is modeled as a sequential state transition problem; that is, vehicle arrival, moving, and departure at a chosen detection area. More specifically, the number of bright pixels and their differences, in a chosen area of interest, are calculated and fed into the proposed state machine to detect vehicles. After a vehicle is detected, the location of the headlights is determined using the downhill simplex method. In the proposed optimization process, various headlights were evaluated for possible headlight positions on the detected vehicles; allowing for an optimal headlight position to be located. Simulation results were provided to show the robustness of the proposed approach for nighttime vehicle and headlight detection.

• 대한원격탐사학회지
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• 제21권2호
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• pp.135-143
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• 2005

최근 고해상도 영상의 공급에 있어 물리적 센서 모델의 대안으로서 RPC(Rational Polynomial Camera) 모델이 활발히 이용되고 있다. RPC 모델을 통하여 지상 좌표와 영상 좌표간의 ,기하 관계를 단순하고도 정확하게 묘사할 수 있어 과거 물리적 센서 모델을 통하여만 이루어질 수 있었던 정사보정, 스테레오 영상을 이용한 3차원 좌표 추출 등의 처리가 가능하게 되었다 본 연구에서는 RPCs(Rational Polynomial Coefficients)가 주어진 스테레오 영상으로부터 3차원 좌표를 추출할 수 있는 매우 간단한 방법을 제안하고자 하였다. 제안된 방법은 Downhill Simplex 기법을 이용하는 방법으로서, Downhill Simplex 기법은 함수의 최소값을 찾는데 있어 편미분 계산을 수행하지 않는다는 장점을 가지고 있다. 본 연구에서 제안된 Downhill Simplex 기법을 이용한 RPC 스테레오 영상으로부터의 3차원 좌표 추출 기법은 실제 사용이 가능한 소프트웨어 프로그램으로서 구현되었으며, 서울 지역의 스테레오 IKONOS 영상에 시험 적용되었다. 시험 적용 결과, 본 방법은 비교적 빠르게 3차원 좌표를 계산할 수 있는 것으로 평가되며, RPCs가 주어진 스테레오 영상으로부터 3차원 좌표를 추출할 수 있는 실제적 기술로서 사용이 가능할 것으로 기대된다.

• 대한의용생체공학회:의공학회지
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• 제29권3호
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• pp.231-238
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• 2008

Nelder-Mead downhill simplex method (DSM), a kind of deterministic optimization algorithms, has been used extensively for magnetoencephalography(MEG) dipolar source localization problems because it dose not require any functional differentiation. Like many other deterministic algorithms, however, it is very sensitive to the choice of initial positions and it can be easily trapped in local optima when being applied to complex inverse problems with multiple simultaneous sources. In this paper, some modifications have been made to make up for DSM's limitations and improve the accuracy of DSM. First of all, initial point determination method for DSM using magnetic fields on the sensor surface was proposed. Secondly, Univariant-DSM combined DSM with univariant method was proposed. To verify the performance of the proposed method, it was applied to simulated MEG data and practical MEG measurements.

• Current Optics and Photonics
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• 제6권2호
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• pp.161-170
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• 2022

Three-dimensional (3D) geometric models are introduced to correct vignetting, and a downhill simplex search is applied to determine the coefficients of a 3D model used in digital microscopy. Vignetting is nonuniform illuminance with a geometric regularity on a two-dimensional (2D) image plane, which allows the illuminance distribution to be estimated using 3D models. The 3D models are defined using generalized polynomials and arbitrary coefficients. Because the 3D models are nonlinear, their coefficients are determined using a simplex search. The cost function of the simplex search is defined to minimize the error between the 3D model and the reference image of a standard white board. The conventional and proposed methods for correcting the vignetting are used in experiments on four inspection systems based on machine vision and microscopy. The methods are investigated using various performance indices, including the coefficient of determination, the mean absolute error, and the uniformity after correction. The proposed method is intuitive and shows performance similar to the conventional approach, using a smaller number of coefficients.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.277-280
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• 2009

This paper deals with the performance evaluation of Barlat's and BBC yield criteria by the directional variation prediction of the yield stresses and the R-values. for the evaluation of yield criteria, three kinds of Aluminum alloys and two kinds of steels were selected and their material properties are from Stoughton and Yoon's work. The experimental data required for the parameter evaluation included the uniaxial yield stresses and R-values (width-to-thickness strain ratio in uniaxial tension) measured in rolling direction, diaganol direction and the transverse direction, the equibiaxial yield stress and the R-value of equibiaxial tension. The optimization method, the Downhill Simplex method, was selected for the coefficient identification of Barlat91, Barlat97 and Barlat2000 yield criteria. Yield surface shapes, yield stress and R-value directionalities of Barlat's and BBC yield criteria were investigated and compared with the experimental data. Barlat2000 and BBC yield criteria were extremely qualified for the shape of the yield surface and the directionality of the yield stresses and the R-values.

• 한국공작기계학회논문집
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• 제11권1호
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• pp.45-51
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• 2002

To reduce the cost and increase reliability of die and mold products, automation of the finishing (polishing) process is essential. A major element of automation is a reliable database and a knowledge base for polishing status. This paper presents a polishing expert system which can determine optimal polishing sequences and conditions by using an empirical formula and an experimental database. The simplex method was used for the curve fittings of the experimental results. Also a graphical user interface, which visualizes the optimized results, was developed.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 신호처리소사이어티 추계학술대회 논문집
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• pp.237-240
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• 2003

We implement a system for 3D structure reconstruction from multiple 2D images. It uses geometric primitives such as box, wedge, pyramid, etc, each having translation, rotation, and scale parameters. Primitives are marked on input images with GUI (Graphic User Interface). Lines made by projection of primitives onto an image correspond to marked line segments of the image. Error function is defined by disparity between them and is minimized by downhill simplex method. By assigning relationship between models, the number of parameters to solve can be decreased and the resultant models become more accurate To share variables among other models also reduces computational complexity. Experiments using real images have shown that the proposed method successfully reconstructs 3D structure.