• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 심포지엄 논문집 정보 및 제어부문
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• pp.152-154
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• 2007

Anew discretization method for the input-driven nonlinear continuous-time system with time delay is proposed. It is based on the combination of Taylor series expansion and first-order hold assumption. The mathematical structure of the new discretization scheme is explored. The performance of the proposed discretization procedure is evaluated by case studies. The results demonstrate that the proposed discretization scheme can assure the system requirements even though under a large sampling period. A comparison between first order hold and zero-order hold is simulated also.

• 데이타베이스연구회지:데이타베이스연구
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• 제34권3호
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• pp.159-169
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• 2018

연속형 변수의 이산화(Discretization)는 양적 변수(Quantitative variable)를 질적 변수(Qualitative variable)로 변형시켜 데이터 마이닝(Data mining) 기법 등 다양한 알고리즘의 성능을 향상시키는데 사용 목적이 있다. 데이터에 적절한 이산화 기법을 사용한다면 분류 알고리즘에 대해 더 좋은 성능뿐 아니라 간결한 결과 해석, 속도 향상까지 기대할 수 있다. 현재까지 다양한 이산화 기법들이 연구되었으며, 현재도 이산화와 관련한 연구에 수요가 많다. 본 논문은 데이터의 클래스에 대한 연속형 변수 값의 분포를 고려하여, Wasserstein 거리를 이용해 분할점을 자동 설정하는 이산화 기법을 제안한다. 본 논문에서 제안하는 기법과 우수함이 입증된 기존의 이산화 기법에 대해 성능비교를 통해 제안 기법의 우수성을 보인다.

• Journal of the Korean Data and Information Science Society
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• 제28권6호
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• pp.1547-1555
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• 2017

This paper studies Bayesian test of homogeneity in contingency tables made by discretizing a continuous variable. Sometimes when we are considering events of interest in small area setup, we can think of discretization approaches about the continuous variable. If we properly discretize the continuous variable, we can find invisible relationships between areas (groups) and a continuous variable of interest. The proper discretization of the continuous variable can support the alternative hypothesis of the homogeneity test in contingency tables even if the null hypothesis was not rejected through k-sample tests involving one-way ANOVA. In other words, the proportions of variables with a particular level can vary from group to group by the discretization. If we discretize the the continuous variable, it can be treated as an analysis of the contingency table. In this case, the chi-squared test is the most commonly employed method. However, further discretization gives rise to more cells in the table. As a result, the count in the cells becomes smaller and the accuracy of the test becomes lower. To prevent this, we can consider the Bayesian approach and apply it to the setup of the homogeneity test.

• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1297-1305
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• 2004

In this paper, we propose a new scheme for the discretization of nonlinear systems using Taylor series expansion and the zero-order hold assumption. This scheme is applied to the sampled-data representation of a non-affine nonlinear system with constant input time-delay. The mathematical expressions of the discretization scheme are presented and the ability of the algorithm is tested for some of the examples. The proposed scheme provides a finite-dimensional representation for nonlinear systems with time-delay enabling existing controller design techniques to be applied to them. For all the case studies, various sampling rates and time-delay values are considered.

• International Journal of Aeronautical and Space Sciences
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• 제14권2호
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• pp.122-132
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• 2013

In this research the development of unstructured grid discretization solution techniques is presented. The purpose is to describe such a conservative discretization scheme applied for experimental validation work. The objective of this paper is to better establish the effects of mesh generation techniques on velocity fields and particle deposition patterns to determine the optimal aerodynamic characteristics. In order to achieve the objective, the mesh surface discretization approaches used the VLA prototype manufacturing tolerance zone of the outer surface. There were 3 schemes for this discretization study implementation. They are solver validation, grid convergence study and surface tolerance study. A solver validation work was implemented for the simple 2D and 3D model to get the optimum solver for the VLA model. A grid convergence study was also conducted with a different growth factor and cell spacing, the amount of mesh can be controlled. With several amount of mesh we can get the converged amount of mesh compared to experimental data. The density around surface model can be calculated by controlling the number of element in every important and sensitive surface area of the model. The solver validation work result provided the optimum solver to employ in the VLA model analysis calculation. The convergence study approach result indicated that the aerodynamic trend characteristic was captured smooth enough compared with the experimental data. During the surface tolerance scheme, it could catch the aerodynamics data of the experiment data. The discretization studies made the validation work more efficient way to achieve the purpose of this paper.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제16권1호
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• pp.60-64
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• 2010

비 트랜잭션 데이터를 대상으로 연관 규칙을 도출하기 위해서, 데이터의 속성들을 구간화하는 기법들이 활발하게 연구되었다. 이러한 기존의 연구들은 구간화 단계에서 구간 범위의 변화에 따른 연관 규칙의 신뢰도 변화를 반영하지 않고, 구간화 단계와 연관 규칙을 도출하는 단계들을 독립적으로 수행하였다. 이로 인해 속성들의 구간이 부적절하게 설정되고, 이 결과 높은 신뢰도를 갖는 연관 규칙들이 최종 결과에서 누락된다. 따라서 본 논문에서는 속성들을 구간화하는 단계와 연관 규칙들을 도출하는 단계를 병합하여 동시에 수행함으로써, 가장 신뢰도가 높은 연관규칙들을 도출할 수 있는 구간을 설정하는 방안을 제안한다. 이를 위해서 연관 규칙의 우변의 속성들을 대상으로 계층적 클러스터링을 수행하고, 각 클러스터들에 대해서 특성 분석을 수행한다. 실험 결과, 제안하는 기법은 기존의 기법들에 비해서 높은 신뢰도를 갖는 연관 규칙들을 발견하는 것으로 나타났다.

• 한국수학교육학회지시리즈B:순수및응용수학
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• 제14권4호
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• pp.283-287
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• 2007

An extension of the contraction mapping theorem is provided in a Banach space setting to approximate fixed points of operator equations. Our approach is justified by numerical examples where our results apply whereas the classical contraction mapping principle cannot.

• Journal of Electrical Engineering and Technology
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• 제12권6호
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• pp.2399-2410
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• 2017

In this paper, a linear matrix inequality-based sampled-data fuzzy observer design method is proposed based on the exact discretization approach. In the proposed design technique, a numerically relaxed observer design condition is obtained by using the discrete-time fuzzy Lyapunov function. Unlike the existing studies, the designed observer is robust to the uncertain premise variable because the fuzzy observer is designed under the imperfect premise matching condition, in which the membership functions of the system and observer are mismatched. In addition, we apply the proposed method to the state estimation problem of the attitude and heading reference system (AHRS). To do this, we derive a Takagi-Sugeno fuzzy model for the AHRS system, and validate the proposed method through the hardware experiment.

• 응용통계연구
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• 제26권2호
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• pp.307-319
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• 2013

마이크로어레이 실험의 특성상 표본의 수가 많지 않는 단점을 보완하고 분석 결과를 일반화하기 위하여 공개 저장소에 축적된 자료 중에 연구 목적이 동일한 여러 연구들을 통합하여 분석하려는 시도가 활발하다. 그러나 실험에서 사용한 플랫폼이 서로 다른 경우에는 유전자 관찰값의 분포가 달라지기 때문에 통합이 어렵고 최상의 통합 방법이 제시되어 있지 않다. 본 논문에서는 순위 기반 중위수, 분위수 이산화와 표준화를 각각 이용하여 변환한 자료값을 직접 합치거나 메타분석을 하여 연구 결과를 합치는 방법을 알아 보았다. 또한 GEO에서 다운받은 실제 자료들을 이용하여 네 가지 방법의 장단점과 효과를 비교하였고 서로 다른 연구 자료를 통합하는 것의 영향을 알아보았다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전력기술부문
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• pp.252-255
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• 2001

Modern power systems are very complex and to model them completly is impractical for electromgnetic transient studies. Therefore areas outside the immediate area of interest must be represented by some form of Frequency Dependent Network Equivalent (FDNE). In this paper a method for developing FDNE is presented and demonstrated. The FDNE is generated by Linearized Least Square fitting the frequency response of a z-domain formulation. The advantage of this approach is that a direct implementation occurs which dose not incur errors due to discretization inherent with implementing a fitting function in the s-domain. The developed FDNE is accurate and efficient.