一类非张量积区域快速傅立叶变换算法在匡产并行机上的可扩展性测试

本文给出了一类基于六边形非张量积区域上的广义离散快速傅立叶变换算法（HFFT）以及它在国产百万亿次超级计算机（曙光5000A）上的测试运行情况．文章介绍了该算法在曙光5000A上的大规模集群测试加速比和可扩展性特性,并通过分析,说明HFFT在国产超级计算机的大规模并行环境下拥有良好的可扩展性．在使用8192个处理器核的情况下,HFFT加速比达到了277倍．我们同样对FFTw软件包进行了测试．本文的分析为解决其他科学计算程序在国产百万亿次规模集群上的可扩展性问题,提供了一些先行的参考和建议．     

eXist数据库结构连接算法的改进和实现

为了进一步提高eXist数据库的查询效率,针对数据库现有的数据存储特点和查询策略,提出一种快速定位的结构连接算法FL-Stack。算法采用栈缓存已遍历过的但仍可能与尚未遍历的后代结点匹配的祖先结点,并对能预先判断不可能满足结构连接匹配的祖先或后代结点,提出相应方法实现快速定位,以批量跳过这类结点。与现有算法必须逐个扫描祖先后代结点序列相比,这种快速定位的结构连接算法避免了逐个扫描带来的多次重复无意义的比较,可大大提高结构连接效率。     

Fast kernel conditional density estimation: A dual-tree Monte Carlo approach

We describe a fast, data-driven bandwidth selection procedure for kernel conditional density estimation (KCDE). Specifically, we give a Monte Carlo dual-tree algorithm for efficient, error-controlled approximation of a cross-validated likelihood objective. While exact evaluation of this objective has an unscalable O(n²) computational cost, our method is practical and shows speedup factors as high as 286,000 when applied to real multivariate datasets containing up to one million points. In absolute terms, computation times are reduced from months to minutes. This enables applications at much greater scale than previously possible. The core idea in our method is to first derive a standard deterministic dual-tree approximation, whose loose deterministic bounds we then replace with tight, probabilistic Monte Carlo bounds. The resulting Monte Carlo dual-tree algorithm exhibits strong error control and high speedup across a broad range of datasets several orders of magnitude greater in size than those reported in previous work. The cost of this high acceleration is the loss of the formal error guarantee of the deterministic dual-tree framework; however, our experiments show that error is still amply controlled by our Monte Carlo algorithm, and the many-order-of-magnitude speedups are worth this sacrifice in the large-data case, where cross-validated bandwidth selection for KCDE would otherwise be impractical.     

基于多指标的指纹图像质量综合评估研究

结合空域和频域特征的质量评估方法评估指纹图像质量。分割出指纹图像有效区域,分析该有效区域的面积、偏移度、干湿度等局部质量评估指标,并对其中心区域进行快速傅里叶变换获得全局质量评估指标,通过非线性加权融合5个质量评估指标的评估分数得到指纹图像的综合质量评估分数。实验结果表明,该方法能准确判断指纹图像的质量,有助于提高自动指纹识别系统的整体性能。     

Multilevel augmentation algorithms based on fast collocation methods for solving ill-posed integral equations

This paper continues the theme of the recent work Chen et al. (2008) [18], in which fast collocation methods are introduced for solving ill-posed Fredholm integral equations of the first kind. We develop in this paper multilevel augmentation algorithms, which lead to fast solutions of the discrete equations resulting from fast collocation methods. Regularization parameter choice strategies are given for proposed methods. The theoretical analysis and numerical experiments illustrate the accuracy and efficiency of the algorithm.     

A numerical modelling for the extraction of decay regions from color images of monuments

An innovative application focused on the segmentation of decay zones from images of stone materials is presented. The adopted numerical approach to extract decay regions from the color images of monuments provides a tool that helps experts analyze degraded regions by contouring them. In this way even if the results of the proposed procedure depend on the evaluation of experts, the approach can be a contribution to improving the efficiency of the boundary detection process. The segmentation is a process that allows an image to be divided into disjoint zones so that partitioned zones contain homogeneous characteristics. The numerical method, used to segment color images, is based on the theory of interface evolution, which is described by the eikonal equation. We adopted the fast marching technique to solve the upwind finite difference approximation of the eikonal equation. The fast marching starts from a seed point in the region of interest and generates a front which evolves according to a specific speed function until the boundary of the region is identified. We describe the segmentation results obtained with two speed functions, attained by the image gradient computation and color information about the object of interest. Moreover, we present the extension of the working modality of the method by introducing the possibility to extract the regions not only in a local way but also in a global way on the entire image. In this case, in order to improve the segmentation efficiency the application of the fast marching technique starts with more seed points defined as seed regions. The study case concerns the impressive remains of the Roman Theatre in the city of Aosta (Italy). In the image segmentation process the color space L^∗a^∗b^∗$L^{\ast }{a}^{\ast }{b}^{\ast }$ is utilized.     

Fast Object Segmentation by Growing Minimal Paths from a Single Point on 2D or 3D Images

In this paper, we present a new method for segmenting closed contours and surfaces. Our work builds on a variant of the minimal path approach. First, an initial point on the desired contour is chosen by the user. Next, new keypoints are detected automatically using a front propagation approach. We assume that the desired object has a closed boundary. This a-priori knowledge on the topology is used to devise a relevant criterion for stopping the keypoint detection and front propagation. The final domain visited by the front will yield a band surrounding the object of interest. Linking pairs of neighboring keypoints with minimal paths allows us to extract a closed contour from a 2D image. This approach can also be used for finding an open curve giving extra information as stopping criteria. Detection of a variety of objects on real images is demonstrated. Using a similar idea, we can extract networks of minimal paths from a 3D image called Geodesic Meshing. The proposed method is applied to 3D data with promising results.

VANET中基于移动IPv6的快速切换策略研究

针对车载自组织网络在城市道路车流量大的情况,车辆在不同的路边基站之间频繁地进行上下文切换,从而导致IPv6的移动性支持协议切换时延过长的问题,提出了一种基于代理移动路由的快速切换方案。采用代理移动路由在3G/WiMAX通信域的切换触发其它802.11p通信域内的车辆发生切换的方法,来达到宏切换与微切换相结合的目的,从而实现批量式快速切换。分析结果表明,该方案较现有方案提高了切换效率,减小了切换时延。