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On linear infeasibility arising in intensity-modulated radiation therapy inverse planning

LINEAR ALGEBRA AND ITS APPLICATIONS 2008年第5-6期428卷 1406-1420页

作者： Censor, Yair Ben-Israel, Adi Xiao, Ying Galvin, James M. Univ Haifa Dept Math IL-31905 Haifa Israel State Univ New Jersey RUTCOR Piscataway NJ 08854 USA Thomas Jefferson Univ Hosp Dept Radiat Oncol Med Phys Div Philadelphia PA 19107 USA

Intensity-modulated radiation therapy (IMRT) gives rise to systems of linear inequalities, representing the effects of radiation on the irradiated body. These systems are often infeasible, in which case one settles for an approximate solution, such as an {alpha, beta}-relaxation, meaning that no more than alpha percent of the inequalities are violated by no more than beta percent. For real-world IMRT problems, there is a feasible {alpha, beta}-relaxation for sufficiently large alpha, beta > 0, however large values of these parameters may be unacceptable medically. The {alpha, beta}-relaxation problem is combinatorial, and for given values of the parameters can be solved exactly by mixed integer programming (MIP), but this may be impractical because of problem size, and the need for repeated solutions as the treatment progresses. As a practical alternative to the MIP approach we present a heuristic non-combinatorial method for finding an approximate relaxation. The method solves a linear program for each pair of values of the parameters {alpha, beta} and progresses through Successively increasing values until an acceptable solution is found, or is determined non-existent. The method is fast and reliable, since it consists of solving a sequence of linear programs. (C) 2007 Elsevier Inc. All rights reserved.

关键词： projection algorithms FEASIBILITY CANCER OPTIMIZATION IMRT inequalities intensity modulated radiation therapy linear programming Radiation Effects

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Reconstruction of compact binary images from limited Fourier amplitude data

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 2008年第10期25卷 2600-2607页

作者： Lo, V. L. Millane, R. P. Univ Canterbury Dept Elect & Comp Engn Computat Imaging Grp Christchurch 1 New Zealand

The problem of reconstructing a binary image from undersampled Fourier amplitude data is considered. This problem maps to an image reconstruction problem in x-ray crystallography. The binary constraint is sufficient to overcome the undersampling and enforce uniqueness, but is insufficient in the case of the additional loss of data that can occur in practice. An iterative projection algorithm is developed that uses binary, connectivity, and compactness constraints to solve the image reconstruction problem, Simulations show the utility of the reconstruction algorithm. (C) 2008 Optical Society of America

关键词： Undersampling Reconstructions Binary images image reconstruction projection algorithms additional loss Fourier amplitude Reconstructive Surgical Procedures Reconstruction algorithm

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Transient and steady-state analysis of filtered-x affine projection algorithms with imperfect secondary path estimate

Transient and steady-state analysis of filtered-x affine pro...

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International Symposium on Image and Signal Processing and Analysis

作者： A. Carini G.L. Sicuranza STI-University of Urbino Italy DEEI-Università di Trieste Italy

This paper provides an analysis based on energy conservation arguments of the transient and steady-state behaviors of two filtered-x affine projection algorithms in presence of an imperfect estimation of the secondary paths of an active noise control system. Very mild assumptions are posed on the system model, which is only required to have a linear dependence of the output from the filter coefficients.

关键词： Transient analysis Steady-state Algorithm design and analysis projection algorithms Finite impulse response filter Active noise reduction Nonlinear filters Convergence Adaptive filters Control systems

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Complex-valued FIR seismic migration filter design using Pure and Relaxed projection algorithms

Complex-valued FIR seismic migration filter design using Pur...

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European Signal Processing Conference (EUSIPCO)

作者： Wail A. Mousa Said Boussakta Des McLernon School of Electronic & Electrical Engineering The University of Leeds Leeds United Kingdom

The iterative Pure and Relaxed Projectors are special cases of Vector Space projection Methods (VSPM). Complex-valued FIR digital filter design using Pure and Relaxed Projectors is proposed for designing seismic migration digital filters. Designing FIR digital filters using VSPM, in general, is able to produce feasible solutions satisfying all the desired filter constraints by the use of only two Fast Fourier Transform (FFT) computations. Furthermore, the design algorithm can be directly extended from one-dimensional (1-D) to multi-dimensional (m-D) filters, an advantage not present in many other filter design techniques. In addition, by using the relaxed projectors, one can achieve faster convergence when compared to the pure projectors. The simulation results show that the relaxed projectors for designing such filters will save up to 86.47% of the number of iterations when compared with the pure projectors.

关键词： Finite impulse response filters Algorithm design and analysis projection algorithms Vectors Passband Filtering algorithms Hilbert space

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New affine projection algorithms based on Gauss-Seidel method

New affine projection algorithms based on Gauss-Seidel metho...

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International Symposium on Signals, Circuits and Systems (ISSCS)

作者： F. Albu C. Kotropoulos Z. Cernekova I. Pitas Department of informatics Aristotle University of Thessaloniki Thessaloniki Greece

This paper proposes a robust and stable fast affine projection algorithm based on the Gauss-Seidel method, the so called modified Gauss-Seidel fast affine projection algorithm. The proposed algorithm is generalized for simplified Volterra filters as well. The computational complexity of both the modified Gauss-Seidel fast affine projection algorithm and its generalization for simplified Volterra filters is derived and their performance for acoustic echo cancellation is assessed.

关键词： projection algorithms Gaussian processes Financial advantage program Nonlinear filters Echo cancellers Convergence Robustness Informatics Adaptive filters Stochastic resonance

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Steady-state and transient analysis of multichannel filtered-x affine projection algorithms

Steady-state and transient analysis of multichannel filtered...

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International Conference on Acoustics, Speech, and Signal Processing (ICASSP)

作者： A. Carini G.L. Sicuranza STI University of Urbino Urbino Italy DEEI University of Trieste Trieste Italy

The paper provides an analysis of the steady-state and transient behavior of two filtered-x affine projection algorithms suitable for multichannel active noise control. The analysis relies on energy conservation arguments, it does not apply the independence theory nor does it impose any restriction to the signal distributions. The paper also shows that filtered-x affine projection algorithms always provide a biased estimate of the minimum-mean-square solution of the active noise control problem.

关键词： Steady-state Transient analysis projection algorithms Active noise reduction Algorithm design and analysis Signal analysis Vectors Symmetric matrices Energy conservation Acoustic noise

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Variable step-size NLMS and affine projection algorithms with variable smoothing factor

Variable step-size NLMS and affine projection algorithms wit...

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Midwest Symposium on Circuits and Systems (MWSCAS)

作者： Tao Dai B. Shahrrava Department of Electrical and Computer Engineering University of Windsor Windsor ONT Canada

In this paper, we propose two new variable step-size normalized least mean square (NLMS) and affine projection algorithms (APA) with variable smoothing factor. Simulation results illustrate that the proposed algorithms have faster convergence rate and lower misadjustment error than the existing algorithms with fixed smoothing factor.

关键词： projection algorithms Smoothing methods Signal processing algorithms Adaptive filters Convergence Adaptive signal processing Least squares approximation Computational modeling Computer errors Signal processing

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Gradient projection Algorithm Using Curry's Steplength for Traffic Assignment

Gradient Projection Algorithm Using Curry's Steplength for T...

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International Conference on Intelligent Transportation

作者： Zichuan Li Gang-Len Chang Suhasini Natarajan Department of Civil and Environmental Engineering University of Maryland College Park MD USA

Recent researches have indicated the viability of path-based algorithms for traffic assignment problem and much attention has been received by gradient projection (GP) algorithm. However, the GP algorithm experiences problems near optimal point when trying to obtain high accurate results. To improve its performance near optimal point, this study employs bisection method to find the Curry's steplength of each iteration as so to achieve that goal. A numerical example is provided to demonstrate the advantage of the GP algorithm using Curry's steplength.

关键词： projection algorithms Communication system traffic control Intelligent transportation systems Application software Routing Computer networks Helium Intelligent networks Road transportation Road safety

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Switched Griffiths-Jim beamformer using the affine projection algorithm

Switched Griffiths-Jim beamformer using the affine projectio...

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International Conference on Mechatronics and Machine Vision in Practice (M2VIP)

作者： V. Yoganathan T. J. Moir School of Engineering and Advanced Technology Massey University Auckland New Zealand

Speech controlled applications are now becoming more and more practical due to advances in technology. These applications vary from command and control instruments, video conferencing to robotics. However, their performance decreases when the acquired speech signal is corrupted by background noise. Numerous research has been done in the last two decades to improve their performance. The switched Griffiths-Jim beamformer is one of the well known methods used to reduce background noise (or interference). This algorithm makes use of two adaptive filters and a voice activity detector. The first filter is used as a beam-steering filter which is updated during speech signals and the second filter is used as a noise cancellation filter which is updated during a noise-alone signal. A voice activity detector is used to control the updates of these adaptive filters. Generally, the normalised least mean squares (NLMS) algorithm is used for the adaptive filters. However, it is found that the convergence rate of the NLMS deteriorates for coloured noise under certain non-stationary conditions where the correlation matrix is "stiff". It has been found that the affine projection algorithm will perform better under these conditions. Therefore, a comparison of these two adaptive filters in this beamformer structure will be discussed in this paper.

关键词： projection algorithms Adaptive filters Speech enhancement Background noise Detectors Noise cancellation Command and control systems Instruments Videoconference Robots

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Method of hybrid multi-attribute decision making based on relative entropy weight and projection algorithm

Method of hybrid multi-attribute decision making based on re...

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World Congress on Intelligent Control and Automation (WCICA)

作者： Congjun Rao Jin Peng Zhongcheng Zhang College of Mathematics and Information Science Huanggang Normal University Huanggang Hubei China Institute of Systems Engineering Huazhong University of Science and Technology Wuhan China

The problem of hybrid multi-attribute decision making, which integrates with interval numbers and linguistic fuzzy numbers, and incomplete information on attribute weights, is studied. Based on the relative entropy weight and projection algorithm, a new method of hybrid multi-attribute decision making is presented. First of all, the definitions of closeness degree and relative entropy are given, and the method of transforming the interval numbers and linguistic fuzzy numbers into triangular fuzzy numbers is presented. Secondly, by solving a set of linear programming models whose goals are to maximize the closeness degree, a series of preference weight vectors which are partial for each alternative are obtained, and then the optimal weight vector is got by aggregating the preference weight vectors through establishing a relative entropy weight model. Thirdly, based on this optimal weight vector, the projection algorithm is presented to rank order for all alternatives. Finally, a decision making example is given to demonstrate the feasibility and rationality of this new method.

关键词： Decision making Entropy Vectors projection algorithms Modeling Linear programming Matrices

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