• Title, Summary, Keyword: Gradient method

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Analysis of Turbulent flow using Pressure Gradient Method (압력구배기법을 이용한 난류 유동장 해석)

  • 유근종
    • Journal of the Korean Society of Propulsion Engineers
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    • v.3 no.2
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    • pp.1-9
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    • 1999
  • Applicability of the pressure gradient method which is formulated based on pressure gradient is verified against turbulent flow analysis. In the pressure gradient method, pressure gradient instead of pressure itself is obtained using continuity constraint. Since correct pressure gradient is found only when mass conservation is satisfied, pressure gradient method can reflect physics of flow field properly The pressure gradient method is formulated with semi-staggered grid system which locates each primitive variables on the same grid point but evaluates pressure gradient in-between. This grid system ensures easy programming and reflection of correct physics in analysis. For verifying applicability of this method, the pressure gradient method is applied to turbulent flow analysis with low Reynolds number $\kappa$-$\varepsilon$ model. Turbulent flows include fully developed channel flow, backward-facing step flow, and conical diffuser flow. Prediction results show that the pressure gradient method can be applied to turbulent flow analysis. However, the pressure gradient method requires somewhat long computation time. Proper way to find optimum under-relaxation factor, $\gamma$, is also need to be developed.

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A MEMORY EFFICIENT INCREMENTAL GRADIENT METHOD FOR REGULARIZED MINIMIZATION

  • Yun, Sangwoon
    • Bulletin of the Korean Mathematical Society
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    • v.53 no.2
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    • pp.589-600
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    • 2016
  • In this paper, we propose a new incremental gradient method for solving a regularized minimization problem whose objective is the sum of m smooth functions and a (possibly nonsmooth) convex function. This method uses an adaptive stepsize. Recently proposed incremental gradient methods for a regularized minimization problem need O(mn) storage, where n is the number of variables. This is the drawback of them. But, the proposed new incremental gradient method requires only O(n) storage.

A BLOCKED VARIANT OF THE CONJUGATE GRADIENT METHOD

  • Yun, Jae Heon;Lee, Ji Young;Kim, Sang Wook
    • Journal of the Chungcheong Mathematical Society
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    • v.11 no.1
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    • pp.129-142
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    • 1998
  • In this paper, we propose a blocked variant of the Conjugate Gradient method which performs as well as and has coarser parallelism than the classical Conjugate Gradient method.

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Comparison with two Gradient Methods through the application to the Vector Linear Predictor (두가지 gradient 방법의 벡터 선형 예측기에 대한 적용 비교)

  • Shin, Kwang-Kyun;Yang, Seung-In
    • Proceedings of the KIEE Conference
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    • pp.1595-1597
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    • 1987
  • Two gradient methods, steepest descent method and conjugate gradient descent method, are compar ed through application to vector linear predictors. It is found that the convergence rate of the conju-gate gradient descent method is much faster than that of the steepest descent method.

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GLOBAL CONVERGENCE OF A NEW SPECTRAL PRP CONJUGATE GRADIENT METHOD

  • Liu, Jinkui
    • Journal of applied mathematics & informatics
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    • v.29 no.5_6
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    • pp.1303-1309
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    • 2011
  • Based on the PRP method, a new spectral PRP conjugate gradient method has been proposed to solve general unconstrained optimization problems which produce sufficient descent search direction at every iteration without any line search. Under the Wolfe line search, we prove the global convergence of the new method for general nonconvex functions. The numerical results show that the new method is efficient for the given test problems.

High-Speed Path Planning of a Mobile Robot Using Gradient Method with Topological Information (위상정보를 갖는 구배법에 기반한 이동로봇의 고속 경로계획)

  • Ham Jong-Gyu;Chung Woo-Jin;Song Jae-Bok
    • Journal of Institute of Control, Robotics and Systems
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    • v.12 no.5
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    • pp.444-449
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    • 2006
  • Path planning is a key element in navigation of a mobile robot. Several algorithms such as a gradient method have been successfully implemented so for. Although the gradient method can provide the global optimal path, it computes the navigation function over the whole environment at all times, which result in high computational cost. This paper proposes a high-speed path planning scheme, called a gradient method with topological information, in which the search space for computation of a navigation function can be remarkably reduced by exploiting the characteristics of the topological information reflecting the topology of the navigation path. The computing time of the gradient method with topological information can therefore be significantly decreased without losing the global optimality. This reduced path update period allows the mobile robot to find a collision-free path even in the dynamic environment.

A Novel Line Detection Method using Gradient Direction based Hough transform (Gradient 방향을 고려한 허프 변환을 이용한 직선 검출 방법)

  • Kim, Jeong-Tae
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.56 no.1
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    • pp.197-205
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    • 2007
  • We have proposed a novel line detection method based on the estimated probability density function of gradient directions of edges. By estimating peaks of the density function, we determine groups of edges that have the same gradient direction. For edges in the same groups, we detect lines that correspond to peaks of the connectivity weighted distribution of the distances from the origin. In the experiments using the Data Matrix barcode images and LCD images, the proposed method showed better performance than conventional Methods in terms of the processing speed and accuracy.

Sensible heat flux estimated by gradient method at Goheung bay wetland (고흥만 습지에서 경도법으로 산출한 현열플럭스)

  • Kim, Dong-Su;Kwon, Byung-Hyuk;Kim, Il Kyu;Kang, Dong Hwan;Kim, Kwang-Ho;Kim, Geun-Hoi;Park, Jun-Sang
    • Journal of Fisheries and Marine Sciences Education
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    • v.20 no.2
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    • pp.156-167
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    • 2008
  • Meorological data have been collected to monitor the wetland area in Goheung bay since 2003 and four intensive observations were conducted to study effects of the atmospheric turbulence on the energy budget and the ecological changes. We improved an algorithm to estimate the sensible heat flux with routine data. The sensible heat flux estimated by gradient method was in good agreement with that measured by precision instruments such as surface layer scintillometer and ultrasonic anemometer. Diurnal variations of sensible heat flux showed analogous tendency to those of temperature gradient. When the vertical wind shear of horizontal wind components was weak, even though temperature gradient was strong, the gradient method underestimated the sensible heat flux. A compensation for the cloud will make this gradient method be a helpful tool to monitor the ecosystem without expensive instruments except for weak wind shear and temperature gradient.

Interior Point Methods for Network Problems (An Efficient Conjugate Gradient Method for Interior Point Methods) (네트워크 문제에서 내부점 방법의 활용 (내부점 선형계획법에서 효율적인 공액경사법))

  • 설동렬
    • Journal of the military operations research society of Korea
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    • v.24 no.1
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    • pp.146-156
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    • 1998
  • Cholesky factorization is known to be inefficient to problems with dense column and network problems in interior point methods. We use the conjugate gradient method and preconditioners to improve the convergence rate of the conjugate gradient method. Several preconditioners were applied to LPABO 5.1 and the results were compared with those of CPLEX 3.0. The conjugate gradient method shows to be more efficient than Cholesky factorization to problems with dense columns and network problems. The incomplete Cholesky factorization preconditioner shows to be the most efficient among the preconditioners.

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Gradient Fusion Method for Night Video Enhancement

  • Rao, Yunbo;Zhang, Yuhong;Gou, Jianping
    • ETRI Journal
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    • v.35 no.5
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    • pp.923-926
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    • 2013
  • To resolve video enhancement problems, a novel method of gradient domain fusion wherein gradient domain frames of the background in daytime video are fused with nighttime video frames is proposed. To verify the superiority of the proposed method, it is compared to conventional techniques. The implemented output of our method is shown to offer enhanced visual quality.