介质涂敷电大尺寸导体柱电磁散射特性的有限元—快速多极混合？…

采用有限元－快速多极混合算法分析了介质涂层电大尺寸导体柱的电北散射特性。与有限元－矩量法相比,快速多极算法将计算复度从Ｏ（Ｎ＾２）降低到Ｏ（Ｎ＾１．５）,大大加快计算速度,减少存储量。计算表明该混合算法对电大复杂涂敷目标电磁我伯分析是灵活而有效的。     

用于分析电磁散射问题的快速多极算法

介绍了用于分析电磁散射问题的快速多极算法(FMA)和多层快速多极算法(MLFMA)的基本思想与基本步骤。通过计算实例表明,快速多极算法在计算速度和存贮要求方面比矩量法有明显优势,适合于在现有计算机条件下求解电大尺寸目标的散射问题。     

分析电大开口腔体电磁散射的快速混合算法-IPO+FMM

电大尺寸开口腔体结构的高频电磁散射分析是复杂目标RCS分析预测中一项很有意义和难度的工作,提出 一种混合算法-IPO+FMM,将迭代物理光学法与快速多极子方法相结合,对电大尺寸开口腔体进行电磁散射分析,文中对 IPO+FMM混合算法进行理论分析与公式推导,希望在保证分析精度的同时减小计算量,提高计算速度。     

三维电大目标散射求解的多层快速多极子方法

为进一步提高对电大尺寸目标散射求解的能力,详细研究了多层快速多极子方法.重点设计了用于多层快速多极子方法的各种优化方法包括Morton编号、转移因子修正内插技术与外向波重复存储策略.对于未知量数目为N的三维电磁散射,数值实验显示多层快速多极子方法具有O(NlogN)量级的计算量、O(N)量级的存储量,特别适合求解三维电大尺寸目标的电磁散射.利用该方法在单机(内存1Gb)上成功计算了未知量为25万的电大尺寸目标散射.     

FMM算法用于二维复杂散射体的RCS计算

利用快速多极子算法(FMM)计算任意形状二维电大尺寸导体加介质体目标的电磁散射，介质体为镶嵌在电大尺寸金属体上的有耗介质。建立金属一介质体的混合积分方程，用共轭梯度法和场量叠代的方法计算散射场，在叠代过程中用快速多极子方法，大大降低计算时间和减小内存要求。数据结果表明该方法的准确和高效。     

用于分析电磁散射问题的快速多极算法

介绍了用于分析电磁散射问题的快速多极算法（FMA）和多层快速多极算法（MLFMA）的基本思想与基本步骤。通过计算实例表明，快速多极算法在计算速度和存贮要求方面比矩量法有明显优势，适合于在现有计算机条件下求解电大尺寸目标的散射问题。     

快速分析电大腔体电磁散射的混合算法

为提高电大腔体电磁散射分析的效率,提出将迭代物理光学法（IPO）与快速多极子方法（FMM）相结合的混合算法IPO＋FMM,给出该混合算法的数学模型推导,该算法可将每迭代步的计算量由O（N^2）降到O（N^1.5）,最后分析了二种不同形状的电大尺寸腔体的雷达散射截面。数值结果表明,该混合算法与IPO算法相校,精度相当但效率有显著提高。     

一种快收敛的计算三维电大腔体RCS的混合方法——JMRES+RPFMA

雅克比最小残差法(JMRES)是一种快收敛的计算电大腔体电磁散射特性的计算方法,其积分运算的时间复杂度为O(N2),因此引入射线多极子方法加速JMRES的积分运算。利用快速多极子方法中参与计算的有效角谱分量随着组间距离增大而变少的特性,采用一种随着组间距离增大自适应调整参与计算的角谱分量的锥形区域的射线多极子方法来降低积分运算的时间复杂度。计算结果表明该方法是准确的,并能极大地提高计算速度。     

组合导体目标电磁特性的快速多极算法计算

用快速多极算法分析具有任意线、面、体组合的电大尺寸理想导体目标的电磁散射和辐射特性.统一采用RWG基函数对线、面、体导体上的电流进行展开;使用了新的设置基函数和未知量的方法来处理任意的线-面,面-面连接问题;并使用多层快速多极算法结合ILUT预处理算法加速求解过程.数值结果验证了本文方法的准确性和高效性.     

基于混合ACA的缺陷钢轨高效电磁建模

提出了一种基于矩量法(MoM)结合多层快速多极子(MLFMA)和自适应交叉近似(ACA)算法计算目标电磁特性的算法,该算法实现了对电大尺寸复合目标散射计算的加速和内存的降低。对于目标自作用的近场区域,多层快速多极子加速矩量法中的矩阵矢量乘运算,降低了计算的存储和复杂度;对于远场区域,根据阻抗矩阵的低秩特性,采用ACA对其压缩,加速矩阵的填充。矩阵填充按照树形结构划分的单元块间的相互作用依次进行存储,对每一块与块之间的求解采用ACA算法,对矩阵做压缩处理。提出的基于ACA的混合算法能够对2个目标耦合作用的阻抗矩阵进行压缩,缩短矩阵的填充时间并降低内存需求,同时也能够减少迭代求解过程中矩阵向量的计算时间,从而极大缩短电磁散射计算的总时间。数值仿真实验表明该算法比传统方法计算更高效,且计算精确度保持一致。     

Thin-stratified medium fast-multipole algorithm for solvingmicrostrip structures

An accurate and efficient technique called the thin-stratified medium fast-multipole algorithm (TSM-FMA) is presented for solving integral equations pertinent to electromagnetic analysis of microstrip structures, which consists of the full-wave analysis method and the application of the multilevel fast multipole algorithm (MLFMA) to thin stratified structures. In this approach, a new form of the electric-field spatial-domain Green's function is developed in a symmetrical form which simplifies the discretization of the integral equation using the method of moments (MoM). The patch may be of arbitrary shape since their equivalent electric currents are modeled with subdomain triangular patch basis functions. TSM-FMA is introduced to speed up the matrix-vector multiplication which constitutes the major computational cost in the application of the conjugate gradient (CG) method. TSM-FMA reduces the central processing unit (CPU) time per iteration to O(N log N) for sparse structures and to O(N) for dense structures, from O(N³) for the Gaussian elimination method and O(N²) per iteration for the CG method. The memory requirement for TSM-FMA also scales as O(N log N) for sparse structures and as O(N) for dense structures. Therefore, this approach is suitable for solving large-scale problems on a small computer     

区域分裂法在电大尺寸柱体电磁散射中的应用

基于区域分裂算法（ＤＤＭ）提出了一种精确高效的算法。通过沿二维物体表面将原问题分解为若干个相对独立的子问题,使得原问题中的稀疏矩阵变换为各子域中带宽极窄的带状阵,计算时间从Ｏ（Ｎ＾２）下降为Ｏ（Ｎ）。同时,由于每个子域可以单独求解,使内存开销从Ｏ（Ｎ＾２）下降为Ｏ（Ｎ／ｍ）（ｍ为子域个数）,从而可以很好地处理电大尺寸或超大尺寸柱体的散射问题。文中成功地计算了周长为１０万个波长的几个电大尺寸二维柱体     

基于前缀区间集合的IPv6路由查找算法

对IPv6相关的通用型与特定型路由算法进行了分析,重点研究了以BSR为基础的IPv6路由算法在查找和更新时的不平衡问题,提出了基于前缀区间集合的IPv6路由算法。通过对路由前缀（N）进行范围（K）、集合（M）划分以及更新节点自修复提高查询速度、降低不平衡性的影响,具有O(log2N/K)和O(log2N/K+2M)的查询与更新时间复杂度,空间复杂度为O(K+2N)。实验表明,该算法具有良好的查询性能,降低了更新不平衡性的影响。     

A Truncation method for computing slant transforms withapplications to image processing

A truncation method for computing the slant transform is presented. The slant transform truncation (STT) algorithm uses the divide and conquer principle of hierarchical data structures to factorize coherent image data into sparse subregions. In one dimension with a data array of size N=2ⁿ, the truncation method takes a time between O(N) and O(Nlog₂N), degenerating to the performance of the fast slant transform (FST) method in its worst case. In two dimensions, for a data array of size N×N, the one-dimensional truncation method is applied to each row, then to each column of the array, to compute the transform in a time between O(N²) and O(N²log₂N). Coherence is a fundamental characteristic of digital images and so the truncation method is superior to the FST method when computing slant transforms of digital images. Experimental results are presented to justify this assertion     

An improved method for 2-D self-similar image synthesis

We propose a new method called incremental Fourier synthesis to generate 2-D self-similar images based on a 2D fractional Brownian motion (fBm) model. With this method, the stationary increments of fBm are created by a Fourier synthesis method and the increments are added up to generate the nonstationary 2D fBm process. Since the new method takes advantage of the FFT, its computational complexity is only O(N(2)log(2)(N)), and its memory requirement is only O(N(2)) for a self-similar image of size NxN.     

MEI系数的快速算法

不变性测试方程法已被证明是解决电磁问题的一种有效方法。目前电大尺寸问题中ＭＥＩ系数的计算已成为一个瓶颈。提出了一个快速算法用于加速ＭＥＩ系数的计算,它使用快速多极子方法计算测试子的散射场,使得ＭＥＩ系数的计算速度从Ｏ（Ｎ＾２）变为Ｏ（Ｎ＾１．５Ｌｏｇ２Ｎ）。     

快速多极子在任意截面均匀介质柱散射中的应用

采用快速多极子法（FMM）加速后的矩量法（MoM）求解由电磁场等效原理导出的关于均匀介质柱表面等铲电磁流的积分方程,进而计算其电磁散射特性,FMM的引入使计算时间和内存开销都从O(N^2）降到O（N^3/2）,且并不增加多少复杂度。最后给出了一些介质柱体RCS的算例。     

基于梯度场的紧致差分最小二乘面形重建算法

为快速准确根据测得的梯度场重建表面面形，针对基于最小二乘全局积分的重建技术，采用紧致差分算子建立全局最优化的代价函数以提高重建精度，将代价函数表示为Sylvester方程，利用Hessenberg-Schur算法求解，将常用最小二乘全局积分技术的空间和时间复杂度分别从O （N2）和O （N3）降低到O （N）和O （N3/2）。实验结果表明:采用四阶精度的紧致差分算子时，文中算法重建精度比高阶截断误差最小二乘积分法（HFLI）和全局最小二乘法（GLS）提高了一个数量级，采用六阶精度的紧致差分算子时重建精度比基于样条的最小二乘积分法（SLI）提高了一个数量级；鲁棒性优于GLS，弱于HFLI和SLI；重建速度显著优于HFLI和SLI，略优于GLS。     

An Improved Multilevel Green's Function Interpolation Method With Adaptive Phase Compensation

An improved multilevel Green's function interpolation method (MLGFIM) with adaptive phase compensation (APC) is proposed. The difficulty in applying interpolation approaches to the fast varying phase term in the integral equation kernel for full-wave electromagnetic (EM) simulations is eradicated by using the phase compensation and adaptive direction separation (ADS). The multilevel tree structure in MLGFIM keeps the number of direction separation invariant at all levels, attributing to the recursive interpolation with multilevel phase compensation. The proposed MLGFIM-APC in conjunction with the Lagrange-Chebyshev interpolation yield an O(N log N) CPU time and O(N) computer memory requirement for surface scattering problems. By introducing a transition level, the MLGFIM-APC can adaptively incorporate interpolation techniques of conventional interpolation (CI), transition interpolation (TI) and phase-compensation interpolation (PI), corresponding to electromagnetic simulation of problems of small, moderate, and large electrical sizes, respectively. Large-scale microstrip antenna arrays are simulated to illustrate the accuracy and efficiency of the proposed method. It is found that the CPU time scales better than O(N log N) for these co-planar problems.     

Low-complexity sequential lossless coding for piecewise-stationarymemoryless sources

Three strongly sequential, lossless compression schemes, one with linearly growing per-letter computational complexity, and two with fixed per-letter complexity, are presented and analyzed for memoryless sources with abruptly changing statistics. The first method, which improves on Willems' (1994) weighting approach, asymptotically achieves a lower bound on the redundancy, and hence is optimal. The second scheme achieves redundancy of O(log N/N) when the transitions in the statistics are large, and O (log log N/log N) otherwise. The third approach always achieves redundancy of O (√log N/N). Obviously, the two fixed complexity approaches can be easily combined to achieve the better redundancy between the two. Simulation results support the analytical bounds derived for all the coding schemes