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排序方式: 共有3758条查询结果,搜索用时 140 毫秒
1.
Multichannel texture analysis using localized spatial filters   总被引:36,自引:0,他引:36  
A computational approach for analyzing visible textures is described. Textures are modeled as irradiance patterns containing a limited range of spatial frequencies, where mutually distinct textures differ significantly in their dominant characterizing frequencies. By encoding images into multiple narrow spatial frequency and orientation channels, the slowly varying channel envelopes (amplitude and phase) are used to segregate textural regions of different spatial frequency, orientation, or phase characteristics. Thus, an interpretation of image texture as a region code, or carrier of region information, is emphasized. The channel filters used, known as the two-dimensional Gabor functions, are useful for these purposes in several senses: they have tunable orientation and radial frequency bandwidths and tunable center frequencies, and they optimally achieve joint resolution in space and in spatial frequency. By comparing the channel amplitude responses, one can detect boundaries between textures. Locating large variations in the channel phase responses allows discontinuities in the texture phase to be detected. Examples are given of both types of texture processing using a variety of real and synthetic textures  相似文献
2.
Metamodels for Computer-based Engineering Design: Survey and recommendations   总被引:32,自引:0,他引:32  
The use of statistical techniques to build approximations of expensive computer analysis codes pervades much of today’s engineering design. These statistical approximations, or metamodels, are used to replace the actual expensive computer analyses, facilitating multidisciplinary, multiobjective optimization and concept exploration. In this paper, we review several of these techniques, including design of experiments, response surface methodology, Taguchi methods, neural networks, inductive learning and kriging. We survey their existing application in engineering design, and then address the dangers of applying traditional statistical techniques to approximate deterministic computer analysis codes. We conclude with recommendations for the appropriate use of statistical approximation techniques in given situations, and how common pitfalls can be avoided.  相似文献
3.
Consumer trust in an Internet store   总被引:28,自引:0,他引:28  
The study reported here raises some questions about the conventional wisdom that the Internet creates a “level playing field” for large and small retailers and for retailers with and without an established reputation. In our study, consumers recognized differences in size and reputation among Internet stores, and those differences influenced their assessments of store trustworthiness and their perception of risk, as well as their willingness to patronize the store. After describing our research methods and results, we draw some implications for Internet merchants. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献
4.
Neural net robot controller with guaranteed tracking performance   总被引:24,自引:0,他引:24  
A neural net (NN) controller for a general serial-link robot arm is developed. The NN has two layers so that linearity in the parameters holds, but the "net functional reconstruction error" and robot disturbance input are taken as nonzero. The structure of the NN controller is derived using a filtered error/passivity approach, leading to new NN passivity properties. Online weight tuning algorithms including a correction term to backpropagation, plus an added robustifying signal, guarantee tracking as well as bounded NN weights. The NN controller structure has an outer tracking loop so that the NN weights are conveniently initialized at zero, with learning occurring online in real-time. It is shown that standard backpropagation, when used for real-time closed-loop control, can yield unbounded NN weights if (1) the net cannot exactly reconstruct a certain required control function or (2) there are bounded unknown disturbances in the robot dynamics. The role of persistency of excitation is explored.  相似文献
5.
Complex systems modeling via fuzzy logic   总被引:20,自引:0,他引:20  
This paper presents a fuzzy logic approach to complex systems modeling that is based on fuzzy discretization technique. As compared with other modeling methods (both statistical and fuzzy), the proposed approach has the advantages of simplicity, flexibility, and high accuracy. Further, it is easy to use and may be handled by an automatic procedure. Numerical examples are provided to illustrate the performance of the proposed approach.  相似文献
6.
Concept Decompositions for Large Sparse Text Data Using Clustering   总被引:20,自引:0,他引:20  
Unlabeled document collections are becoming increasingly common and available; mining such data sets represents a major contemporary challenge. Using words as features, text documents are often represented as high-dimensional and sparse vectors–a few thousand dimensions and a sparsity of 95 to 99% is typical. In this paper, we study a certain spherical k-means algorithm for clustering such document vectors. The algorithm outputs k disjoint clusters each with a concept vector that is the centroid of the cluster normalized to have unit Euclidean norm. As our first contribution, we empirically demonstrate that, owing to the high-dimensionality and sparsity of the text data, the clusters produced by the algorithm have a certain fractal-like and self-similar behavior. As our second contribution, we introduce concept decompositions to approximate the matrix of document vectors; these decompositions are obtained by taking the least-squares approximation onto the linear subspace spanned by all the concept vectors. We empirically establish that the approximation errors of the concept decompositions are close to the best possible, namely, to truncated singular value decompositions. As our third contribution, we show that the concept vectors are localized in the word space, are sparse, and tend towards orthonormality. In contrast, the singular vectors are global in the word space and are dense. Nonetheless, we observe the surprising fact that the linear subspaces spanned by the concept vectors and the leading singular vectors are quite close in the sense of small principal angles between them. In conclusion, the concept vectors produced by the spherical k-means algorithm constitute a powerful sparse and localized basis for text data sets.  相似文献
7.
Proportionate progress: A notion of fairness in resource allocation   总被引:19,自引:0,他引:19  
Given a set ofn tasks andm resources, where each taskx has a rational weightx.w=x.e/x.p,0<1, aperiodic schedule is one that allocates a resource to a taskx for exactlyx.e time units in each interval [x.p·k, x.p·(k+1)) for allkN. We define a notion of proportionate progress, called P-fairness, and use it to design an efficient algorithm which solves the periodic scheduling problem.This research was supported by NSF Research Initiation Award CCR-9111591, and the Texas Advanced Research Program under Grant No. 91-003658-480.  相似文献
8.
智能单粒子优化算法   总被引:18,自引:0,他引:18  
文中在传统粒子群优化(Particle Swarm Optimization,PSO)算法的基础上,提出了智能单粒子优化算法(Intelligent Single Particle Opti mizer,ISPO).与传统的PSO算法不同,该算法采用了一个粒子在解空间中搜索,粒子的位置矢量被分成一定数量的子矢量,并基于子矢量对粒子进行更新.在子矢量更新过程中,通过分析之前的速度更新情况,引入一种新的学习策略,使粒子在搜索空间中能够动态地调整速度和位置,从而向全局最优靠近.实验表明,此算法对大部分标准复合测试函数都具有很强的全局搜索能力,其寻优能力超过了国际上最近提出的基于PSO的改进算法.  相似文献
9.
Performance evaluation of some clustering algorithms and validity indices   总被引:16,自引:0,他引:16  
In this article, we evaluate the performance of three clustering algorithms, hard K-Means, single linkage, and a simulated annealing (SA) based technique, in conjunction with four cluster validity indices, namely Davies-Bouldin index, Dunn's index, Calinski-Harabasz index, and a recently developed index I. Based on a relation between the index I and the Dunn's index, a lower bound of the value of the former is theoretically estimated in order to get unique hard K-partition when the data set has distinct substructures. The effectiveness of the different validity indices and clustering methods in automatically evolving the appropriate number of clusters is demonstrated experimentally for both artificial and real-life data sets with the number of clusters varying from two to ten. Once the appropriate number of clusters is determined, the SA-based clustering technique is used for proper partitioning of the data into the said number of clusters.  相似文献
10.
A new subspace identification approach based on principal component analysis   总被引:16,自引:0,他引:16  
Principal component analysis (PCA) has been widely used for monitoring complex industrial processes with multiple variables and diagnosing process and sensor faults. The objective of this paper is to develop a new subspace identification algorithm that gives consistent model estimates under the errors-in-variables (EIV) situation. In this paper, we propose a new subspace identification approach using principal component analysis. PCA naturally falls into the category of EIV formulation, which resembles total least squares and allows for errors in both process input and output. We propose to use PCA to determine the system observability subspace, the A, B, C, and D matrices and the system order for an EIV formulation. Standard PCA is modified with instrumental variables in order to achieve consistent estimates of the system matrices. The proposed subspace identification method is demonstrated using a simulated process and a real industrial process for model identification and order determination. For comparison the MOESP algorithm and N4SID algorithm are used as benchmarks to demonstrate the advantages of the proposed PCA based subspace model identification (SMI) algorithm.  相似文献
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