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An efficient algorithm for the non-convex penalized multinomial logistic regression
Kwon, Sunghoon,Kim, Dongshin,Lee, Sangin The Korean Statistical Society 2020 Communications for statistical applications and me Vol.27 No.1
In this paper, we introduce an efficient algorithm for the non-convex penalized multinomial logistic regression that can be uniformly applied to a class of non-convex penalties. The class includes most non-convex penalties such as the smoothly clipped absolute deviation, minimax concave and bridge penalties. The algorithm is developed based on the concave-convex procedure and modified local quadratic approximation algorithm. However, usual quadratic approximation may slow down computational speed since the dimension of the Hessian matrix depends on the number of categories of the output variable. For this issue, we use a uniform bound of the Hessian matrix in the quadratic approximation. The algorithm is available from the R package ncpen developed by the authors. Numerical studies via simulations and real data sets are provided for illustration.
Kwon, Sunghoon,Won, Wangyun,Kim, Jiyong Elsevier 2016 RENEWABLE ENERGY Vol.97 No.-
<P><B>Abstract</B></P> <P>In this study, we aim to develop a superstructure-based optimization model using mixed integer linear programming (MILP) to determine the optimal combination and sizing for a hybrid renewable energy system to be used in an isolated area. The developed model has a three-layered energy structure to reflect the current reality in which energy production and consumption sites are generally separate. A variety of economic factors, including distance between facilities and an installation area, are considered for a more accurate estimation of the total annualized cost. Two types of optimization models, i.e., with and without a battery, are proposed to evaluate the economic and technical effects of a storage device to resolve operation issues caused by intermittent resources. An application case study on Jeju Island, Korea, confirms that the proposed model is suitable for decision making at the planning stage of a renewable energy system.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A superstructure model of isolated power supply system using renewable energy. </LI> <LI> The model has three-layered energy structure. </LI> <LI> Two-types of model, i.e. with and without battery, is developed. </LI> <LI> Diverse energy sources and various economic factors are considered. </LI> <LI> The proposed model was validated through application to Jeju Island, Korea. </LI> </UL> </P>
A small review and further studies on the LASSO
Kwon, Sunghoon,Han, Sangmi,Lee, Sangin The Korean Data and Information Science Society 2013 한국데이터정보과학회지 Vol.24 No.5
High-dimensional data analysis arises from almost all scientific areas, evolving with development of computing skills, and has encouraged penalized estimations that play important roles in statistical learning. For the past years, various penalized estimations have been developed, and the least absolute shrinkage and selection operator (LASSO) proposed by Tibshirani (1996) has shown outstanding ability, earning the first place on the development of penalized estimation. In this paper, we first introduce a number of recent advances in high-dimensional data analysis using the LASSO. The topics include various statistical problems such as variable selection and grouped or structured variable selection under sparse high-dimensional linear regression models. Several unsupervised learning methods including inverse covariance matrix estimation are presented. In addition, we address further studies on new applications which may establish a guideline on how to use the LASSO for statistical challenges of high-dimensional data analysis.
KWON, SUA,JUNG, SUNGHOON Magnolia Press 2017 Zootaxa Vol.4341 No.1
<P>A new species, Iassus psudoulmi sp. nov. Kwon et Jung, and two new records, Iassus lateralis (Matsumura, 1905) and I. iziaslavi (Anufriev, 1977) from Korea are presented. Descriptions, illustrations of the species and a key to the Korean Iassus species are provided. </P>
디지털 VCR을 위한 효율적인 리드-솔로몬 프러덕트 코드 디코더 구조
권성훈(Sunghoon Kwon),신현철(Hyunchul Shin) 한국정보과학회 1998 정보과학회 컴퓨팅의 실제 논문지 Vol.4 No.3
본 논문에서는 디지털 VCR 에서 사용되는 리드-솔로몬 (RS) 프러덕트 코드 (product code)의 디코딩을 위한 효율적인 회로 구조를 제안한다. 제안한 디코더 구조의 두 가지 주된 특징은 다음과 같다. 첫째, 새로운 병렬-하드웨어 구조로 변형 유클리드 알고리듬 (modified Euclid's algorithm) 이 구현되었다. 둘째, 디코더 내부에서 클럭 속도를 두 배로 함으로써 (18 MHz 에서 36 MHz), Chien 탐색 회로의 크기 및 디코딩 지연 시간이 감소하였다. 현행 디지털 VCR 의 사양을 만족하도록 제안한 방법으로 회로를 설계한 결과, 기존의 잘 알려진 설계 방법들에서보다 회로 크기가 40 % 정도 감소되었고, 디코딩 지연 시간도 상당히 감소되었다. In this paper, we propose an efficient architecture of a Reed-Solomon (RS) product code decoder for digital VCRs. The two main features of the proposed RS decoder architecture are as follows. First, modified Euclid's algorithm has been implemented by using a new parallel-hardware architecture. Second, by doubling the internal clock frequency (from 18 MHz to 36 MHz), Chien-search block size and decoding latency have been reduced. The proposed circuit has been designed to satisfy the present digital VCR specifications by using 40 % smaller area than the one based on the well-known previous architectures. Furthermore, decoding latency has been significantly reduced.
이중관형 지중열교환기의 유입유량에 따른 관내 유체흐름특성에 관한 연구
홍성훈(Hong, Sunghoon),한신인(Han, Shinin),정영욱(Jung, Youngwook),권용주(Kwon, Yongju),김종영(Kim, Jongyeong),권순철(Kwon, Soonchul) 한국방재학회 2017 한국방재학회논문집 Vol.17 No.4
지열에너지를 효과적으로 활용하기 위해서는 효율적인 열교환기 설계기술이 필요하다. 기존의 U자형 열교환기는 낮은 열교환효율과 넓은 천공면적에 따른 높은 비용에 의한 문제가 있었다. 이에 비용효율적인 열교환기 개발을 위해 이중관형 지중열교환기를 제안했다. 우리는 이중관형 지중열교환기(2m 단일형, 4m 단일형, 4m 이음형, 6m 단일형, 8m 이음형)를 사용하여 최대70 Lm-1의 유입유량에 대해 5 Lm-1간격으로 관내 유체흐름특성을 파악하였다. 실험결과 열교환기길이와 유입유량의 증가에 따라 손실수두도 증가했다. 상용화조건인 50 m 열교환기에 대해 회귀분석한 결과 100 Lm-1유량일 때의 손실수두는 1,120 cm,레이놀드 수는 65,690로 나타나 열교환기 내에서 강한 와류를 일으킬 것으로 나타났다. For utilizing geothermal heat energy efficiently, manufacturing technology for energy-efficient heat exchanger is needed. Conventional U-type heat exchangers have both low efficiency of heat exchange and high cost due to large boring area. Herein, to develop cost-friendly heat exchanger, we introduce double pipe heat exchanger. For this purpose, we used a double pipe (2 m single, 4 m single, 4 m (2+2 m) connection, 6 m single, and 8 m (4+4 m) connection) to figure out the characteristics of flow tendency by controlling influent flow rate up to 70 Lm-1 at the interval of 5 Lm-1. Experimental results showed that head loss increased as the length of heat exchanger and influent flow increased. In the result of regression analysis at the practical condition of flow rate (100 Lm-1) and depth (50 m), head loss and Reynolds number were expected to be 1,120 cm and 65,690, respectively, indicating strong vortex in the double pipe heat exchanger.
Jongok Lim,Minyoung Kim,Sunghoon Jung,Il-kwon Kim,Jong-su Lim,Shin-young Park,Gyeong-mi Kim,Cheolhak Kim,Bong-kyu Byun,Bong-woo Lee,Seunghwan Lee 한국응용곤충학회 2011 한국응용곤충학회 학술대회논문집 Vol.2011 No.10
Larval stages of Callipogon relictus (Semenov) (Coleoptera: Cerambycidae), a gigantic longhorn beetle designated as a natural monument of Korea, has never been studied as it is hardly discovered in nature. The DNA barcoding gene, mt-COI, was used to identify a dead larva found in the Gwangneung forest of the Korea National Arboretum. Based on the result, we provide the morphology of the immature stage, with the illustrations of diagnostic characteristics.