• Title, Summary, Keyword: iterative method

Search Result 1,885, Processing Time 0.046 seconds

Performance Test of the Iterative Method and Newly Developed True X Method (PET 검사에서 Iterative 재구성 방법과 True X 재구성 방법에 따른 영상의 균일성 및 대조도 비교 평가)

  • Choi, Jae-Min;NamKung, Chang-Kyeong;Park, Seung-Yong;Nam, Ki-Pyo;Lim, Ki-Cheon
    • The Korean Journal of Nuclear Medicine Technology
    • /
    • v.13 no.1
    • /
    • pp.20-24
    • /
    • 2009
  • Objective: In this study, the differences between two reconstruction methods were analyzed by comparing image uniformity and contrast according to Iteration and Subset, which were altered through the Iterative method and True X method, used in Siemens' PET/CT studies. Methods: The Phantom images were obtained by exposure for two minutes per one bed. To determine the image uniformity, the Coefficient of variance was used. Also, in order to compare the contrast value, we measured and analyzed the ratio of the SUV mean of Phantom image's hot spheres and the background. Results: Under the same reconstruction conditions (Iteration and Subset) of CV, the Iterative method was higher than the True X method. In the comparison of the SUV mean ratio of the background and hot sphere, the True X method had a closer rate than the Iterative method. Conclusion: The newly developed True X reconstruction method is better than the previously used Iterative method in terms of uniformity and contrast. However, the date for this study was only obtained using the Phantom device. In order to obtain more accurate and useful information from the experiment, further research should be conducted. Also, it is necessary to find the appropriate standards for Iteration and Subset for further experimentation.

  • PDF

An Iterative Watermarking Method Using Human Visual System (인간 시각 시스템을 이용한 반복적 워터마킹 기법)

  • 김희정;김지홍
    • Proceedings of the IEEK Conference
    • /
    • /
    • pp.267-270
    • /
    • 2002
  • In this paper, a new watermarking method using an iterative scheme is proposed. The proposed method consists of two parts: watermark generation and its insertion. In the watermark generation, random signals with normalized distribution N(0,1) are produced and modified using an iterative scheme. In the watermark insertion, the resulting watermark signals are inserted into selected transform coefficients with various scaling parameters in order to achieve the invisibility and robustness against illegal attacks. The simulation results show that the proposed method has good performance for various attacks including image compression, filtering, etc.

  • PDF

A Controller Design of Bilinear Systems via Iterative Method (반복법에 의한 쌍선형 시스템의 제어기 설계)

  • 이돈구;김주식;이상혁
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
    • /
    • v.17 no.5
    • /
    • pp.88-93
    • /
    • 2003
  • This paper presents a controller design method of bilinear systems via iterative method. The iterative procedure with auxiliary sequences is defined in the process of constructing coupled linear time varying systems from bilinear systems. To design the feedback controller for bilinear systems with quadratic cost function, an optimization procedure is given by the representation closely related to the Riccati approach. In the simulation results, it is shown that the suggested method accomplishes the improved performance and good convergence.

Regularized Iterative Image Restoration with Relaxation Parameter (이완변수를 고려한 영상의 정칙화 반복 복원)

  • 홍성용;이태홍
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.19 no.1
    • /
    • pp.91-99
    • /
    • 1994
  • We proposed the regularized iterative restoration method considering relaxation parameter and regularization paramenter in order to restore the noisy motion-blurred images. We used (i-H) as a regularization operator and these two kinds of constraints were applied while conventional regularization iterative restoration method proposed by Jan Biemond et al used the 2-D Laplacian filter and a predetermined regularization parameter value and relaxation parameter to 1. Through the experimental results, we showed better results compared with those by a conventional method and or regularized iterative restoration method just considering only a regularization parameter. These two kinds of constratints have good effects when applied into the regularized iterative restoration method for noisy motion-blurred images.

  • PDF

Comparison of different iterative schemes for ISPH based on Rankine source solution

  • Zheng, Xing;Ma, Qing-wei;Duan, Wen-yang
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • v.9 no.4
    • /
    • pp.390-403
    • /
    • 2017
  • Smoothed Particle Hydrodynamics (SPH) method has a good adaptability for the simulation of free surface flow problems. There are two forms of SPH. One is weak compressible SPH and the other one is incompressible SPH (ISPH). Compared with the former one, ISPH method performs better in many cases. ISPH based on Rankine source solution can perform better than traditional ISPH, as it can use larger stepping length by avoiding the second order derivative in pressure Poisson equation. However, ISPH_R method needs to solve the sparse linear matrix for pressure Poisson equation, which is one of the most expensive parts during one time stepping calculation. Iterative methods are normally used for solving Poisson equation with large particle numbers. However, there are many iterative methods available and the question for using which one is still open. In this paper, three iterative methods, CGS, Bi-CGstab and GMRES are compared, which are suitable and typical for large unsymmetrical sparse matrix solutions. According to the numerical tests on different cases, still water test, dam breaking, violent tank sloshing, solitary wave slamming, the GMRES method is more efficient than CGS and Bi-CGstab for ISPH method.

An Incompressible Flow Computation by a Hierarchical Iterative and a Modified Residual Method (계층적 반복과 수정 잔여치법에 의한 비압축성 유동 계산)

  • Kim J. W.
    • Journal of computational fluids engineering
    • /
    • v.9 no.3
    • /
    • pp.57-65
    • /
    • 2004
  • The incompressible Navier-Stokes equations in two dimensions are stabilized by a modified residual method, and then discretized by hierarchical elements. The stabilization is necessary to escape from the Ladyzhenskaya-Babuska-Brezzi(LBB) constraint and hence to achieve an equal order formulation. To expedite a standard iterative method such as the conjugate gradient squared(CGS) method, a preconditioning technique called the Hierarchical Iterative Procedure(HIP) has been applied. In this paper, we increased the order of interpolation within an element up to cubic. The hierarchical elements have been used to achieve a higher order accuracy in fluid flow analyses, but a proper efficient iterative procedure for higher order finite element formulation has not been available so far The numerical results by the present HIP for the lid driven cavity flow and others showed the present procedure to be stable, very efficient and useful in flow analyses in conjunction with hierarchical elements.

On Robust MMSE-Based Filter Designs for Multi-User Peer-to-Peer Amplify-and-Forward Relay Systems (증폭 및 전달 릴레이 기반 다중 사용자 피어투피어 통신 시스템에서 강인한 MMSE 필터 설계 방법)

  • Shin, Joonwoo
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.38A no.9
    • /
    • pp.798-809
    • /
    • 2013
  • In this paper, we propose robust relay and destination filter design methods for the multi-user peer-to-peer amplify-and-forward relaying systems while taking imperfect channel knowledge into consideration. Specifically, the relay and destination filter sets are developed to minimize the sum mean-squared-error (MSE). We first present a robust joint optimum relay and destination filter calculation method with an iterative algorithm. Motivated by the need to reduce computational complexity of the iterative scheme, we then formulate a simplified sum MSE minimization problem using the relay filter decomposability, which lead to two robust sub-optimum non-iterative design methods. Finally, we propose robust modified destination filter design methods which require only local channel state information between relay node and a specific destination node. The analysis and simulation results verify that, compared with the optimum iterative method, the proposed non-iterative schemes suffer a marginal loss in performance while enjoying significantly improved implementation efficiencies. Also it is confirmed that the proposed robust filter design methods provide desired robustness in the presence of channel uncertainty.

AN ITERATIVE ALGORITHM FOR SOLVING THE LEAST-SQUARES PROBLEM OF MATRIX EQUATION AXB+CYD=E

  • Shen, Kai-Juan;You, Chuan-Hua;Du, Yu-Xia
    • Journal of applied mathematics & informatics
    • /
    • v.26 no.5_6
    • /
    • pp.1233-1245
    • /
    • 2008
  • In this paper, an iterative method is proposed to solve the least-squares problem of matrix equation AXB+CYD=E over unknown matrix pair [X, Y]. By this iterative method, for any initial matrix pair [$X_1,\;Y_1$], a solution pair or the least-norm least-squares solution pair of which can be obtained within finite iterative steps in the absence of roundoff errors. In addition, we also consider the optimal approximation problem for the given matrix pair [$X_0,\;Y_0$] in Frobenius norm. Given numerical examples show that the algorithm is efficient.

  • PDF

Evaluation of Interference Alignment for MIMO-IC based on IEEE 802.11n (IEEE 802.11n 기반 MIMO-IC의 간섭정렬 성능평가)

  • Bae, Insan;Yun, Heesuk;Kim, Jaemoung
    • Journal of Satellite, Information and Communications
    • /
    • v.8 no.4
    • /
    • pp.47-52
    • /
    • 2013
  • In this paper, The existing interference alignment algorithms were analyzed in Rayleigh fading channel environment. The interference alignment techniques are divided to two parts. First thing is Iterative-method, another is Linear-method. Iterative method needs local channel info, but it has the constraint of iteration. On the other hand Linear-method must have global channel info, but has free of iteration and better performance. This paper evaluates the performance of interference alignment algorithms in Rayleigh fading channel of outdoor environment and WLAN channel based on IEEE 802.11n of indoor environment.