深度优先搜索算法及其改进

对于一些简单的搜索问题或者不便构建启发式搜索算法的问题,深度优先搜索算法常是解决问题的有效办法。首先对深度优先搜索算法的基本原理进行描述,在此基础上分析深度优先搜索算法的不足之处,最后对深度优先搜索算法进行改进,并将改进的深度优先搜索算法应用于农夫过河问题,得到2个可行的解。     

AMD Athlon 600MHz的系统

在龙睡觉的时候,农夫悄悄走近偷走了它的金子。在我们现在介绍的这个事例中,龙是Intel,农夫是AMD,后者新推出的Athlon微处理器(原来称为K7)已经以更高的时钟频率和更好的性能超越了Pentium Ⅲ。     

幸福的味道

有一个人,他生前善良且热心助人,所以在他死后,升上天堂,做了天使。他当了天使后,仍时常到凡间帮助人,希望感受到幸福的味道。一日,他遇见一个农夫,农夫的样子非常困恼,他向天使诉说∶"我家的水牛刚死了,没它帮忙犁田,那我怎能下田作业呢?"于是天使赐他一只健壮的水牛,农夫很高兴,天使在他身上感受到幸福的味道。     

银行的力量

对于现代企业电子商务的一个症结——信誉问题业界曾经有过很多探讨．但是无论务虚到什么程度．总要有人来实实在在地做事．最起码要模着石头过河。     

移动的声音

《IT时代周刊》总第272期,"总编辑随笔",《农夫山泉到底能不能喝?》新浪微博@WOLF托尔斯泰:以前,当我看到食品问题频频爆出时,总会吐槽商家怎样怎样无良,总是会埋怨执法部门不作为,总会惊叹抱怨还有什么是能吃的。如今,当我再次看到食品问题时,先是感到好奇,然后就不以为意了,原因是都已经"习     

农夫山泉“标准门”:一场双输的战争

5月6日下午,农夫山泉在北京召开声势浩大的新闻发布会,宣布关闭在京桶装水工厂,称不会向舆论暴力低头,正义和尊严比金钱更重要。发布会火药味十足,现场发言4次被打断,事件主角农夫山泉与《京华时报》双方正面交锋对质,场面一度混乱。中国饮用水生产商农夫山泉与媒体批评者间的战争,已经打到刺刀见红的阶段:口水仗、场面火爆的新闻发布会、以"喊冤"形式呈现的广告、对"幕后主导者"的追索……这场持续数月的食品安全争议,终于发展为近期最吸引眼球的公共事件之一,没有赢家。     

经济模式的返濮归真

美国有一个南部州,每年都要举办南瓜品种大赛,其中有一个农夫的成绩相当优秀,经常能得到首奖及优等奖。但奇怪的是,他得奖之后,反而向街坊邻居分送得奖的种子,毫不吝惜。自然就有邻居异讶地问他‘你的奖项得来不易,每年我们都看到你投入大量的时间和精力来改良品种,为什么还这么慷慨地把种子送给我们呢？难道你不怕我们的南瓜品种会因此超过你吗？”这位农夫的回答却很有一种“社会主义精神”：“我把种子分送给大家,帮助大家,其实也就是帮助我自己！”原来,这位农夫所居住的城镇是典型的农村型态,家家户户的田地都比邻相连。如…     

某过河架空电缆钢索大修可行性论证

位于某地境内的电缆线路，过河时采用以铁塔支撑、钢索架挂小同轴电缆的方式。这一段架空电缆如同整个线路的咽喉，稳固与否直接影响到南北干线的畅通。该线段建于1978年4月，至今已有17年，目前主要存在以下几个问题：     

事物的本质

有这样一个故事：蝎子在河边问青蛙能否背它过河,青蛙拒绝了,“我不能背你,因为你会蜇我的”。     

农夫的杰作 Entreq Challenger 2010 USB线、Minimus接地盒

在前段时间,我看到一位发烧友在微信中提及到USB线材对CAS系统声音改善程度的问题。在该微信中,他大幅度地赞扬这款线材,并称能让自己的CAS系统得到前所未有的效果。对于我来说,以往一直都只重视模拟信号线和电源线,却很少关注USB线,所使用的USB线都是一些普通货色。不过,正是这样的一条信息从而激起了我玩USB线的欲望。历经几番波折,我向朋友借来了由瑞典Entreq出品的Challenger2010 USB线和Minimus接地盒套装。关于这个品牌,它有一个很有趣的中文名,叫"音乐农夫"。那是因为Entreq的创始人是一名热爱音响的农民。平时除了务农,空余的时间就是听音乐和制作音响配件。面对这个有趣的品牌,我真的要好好地品尝这位农夫的杰作。     

认知MIMOME系统安全速率最大化算法研究

文章主要从安全速率（secrecy rate）最大化的角度研究了多输入多输出多天线窃听者（Multiple-Input Multiple-Output Multiple-antenna Eavesdropper,MIMOME）认知无线网络的物理层安全问题。针对在次用户的发送信号中加入人工噪声的安全策略,研究了实现系统安全速率最大化的优化问题。该优化问题属于非凸问题,本文提出了一种双层迭代优化算法,将内层问题通过求解一系列的半正定问题进行有效处理,而将外层问题变换为一个单变量的优化,从而通过一维搜索得到最优解。进一步,将该优化求解算法扩展到非理想信道状态信息情况,采用基于最差情况下的鲁棒人工噪声设计,保证在椭球不确定集内的所有信道实现均能够满足。最后仿真验证了该优化算法在理想和非理想信道状态信息下算法的有效性,与迫零人工噪声预编码优化算法相比,该算法可获得更高的安全速率。      

Minimax design of two-dimensional parallelogram filter banks

The authors present a technique for the minimax design of two-dimensional (2-D) parallelogram filter bank (PFB) systems with linear-phase analysis/synthesis filters. To achieve perfect reconstruction, the required analysis filters must have parallelogram-shaped frequency responses. In general, the original design problem is found to be an optimisation problem with nonlinear constraints. The authors present a linearisation approach to reformulate the design problem. As a result, updating the filter coefficient vector at each iteration for the original design problem can be accomplished by searching the gradient of the linearised optimisation problem. They further present an efficient method based on a modified Karmarkar's algorithm for computing the required gradient vector and finding the required step size analytically. Therefore the filter coefficients can easily be computed by solving only linear equations at each iteration during the design process. The effectiveness of the proposed technique is shown by computer simulations     

关于遍历矩阵密码体制的安全性

分析了基于有限域遍历矩阵的公钥密码体制的安全性。根据公钥,采取逆矩阵消去方法得到伪造私钥的线性方程组。从而证明了计算性TEME问题是多项式时间可解的,利用伪造私钥即可破解PZZ1密码体制的密文。在一些情况下,SEME问题在多项式时间内可归约为离散对数问题,若密钥参数选取不当,PZZ2密码体制是基于离散对数问题的,并不基于NP困难问题。     

Closed-form mapping conditions for the synthesis of linear processor arrays

This paper addresses the problem of mapping algorithms with constant data dependences to linear processor arrays. The closed-form necessary and sufficient mapping conditions are derived to identify mappings without computational conflicts and data link collisions. These mapping conditions depend on the space-time mapping matrix and the problem size parameters only. Their correctness can be verified in constant time that is independent of problem size. The design of optimal linear processor arrays is formulated as a mathematic programming problem, which can be solved efficiently by a systematic enumeration of a polynomial search space.     

Time-domain imaging of radar targets using sinogram restoration forlimited-view reconstruction

The time-domain image reconstruction problem can be formulated as a sinogram recovery problem. The sinogram recovery problem is to find a complete sinogram based on the measured incomplete sinogram. In this paper, we solve the sinogram recovery problem by using linear prediction techniques. Since the scattered field of a target can be written as a superposition of distinct specular reflections arising from scattering centers on the target, the trace of the scattering centers can be predicted using linear prediction with the change of the observation angle. Thus, the missing data may be predicted before reconstructing the image. Some useful results obtained using the proposed method are presented     

网格工作流动态调度研究

现有的网格工作流调度算法大都利用遗传算法所具有的并行性和全局解空间搜索的特点来解决工作流调度问题.但是,现有的调度算法没有对动态调度问题进行处理.文中针对网格服务的动态性,提出了服务资源信息中心的概念并给出了网格工作流管理系统的体系结构.在现有的基于遗传算法的网格工作流调度算法的基础上提出了网格服务工作流动态调度算法,补充了不同工作流过程模型的适应度函数的计算.     

Finding Quadratic Schedules for Affine Recurrence Equations Via Nonsmooth Optimization

Frequently, affine recurrence equations can be scheduled more efficiently by quadratic scheduling functions than by linear scheduling functions. In this paper, the problem of finding optimal quadratic schedules for affine recurrence equations is formulated as a convex nonsmooth programming problem. In particular, sufficient constraints for causality are used generalizing Lamport's condition. In this way, the presented problem formulation becomes independent of the problem size. The research tool AQUAD is described implementing this problem formulation. Several nontrivial examples demonstrate that AQUAD can be effectively used to calculate quadratic schedules for affine recurrence equations. Finally, it is shown how array processors can be synthesized from affine recurrence equations which are scheduled by quadratic functions with a singular Hessian matrix.     

Scheduling sensor activity for information coverage of discrete targets in sensor networks

In this paper, we study the problem of scheduling sensor activity to cover a set of targets with known locations such that all targets can be monitored all the time and the network can operate as long as possible. A solution to this scheduling problem is to partition all sensors into some sensor covers such that each cover can monitor all targets and the covers are activated sequentially. In this paper, we propose to provide information coverage instead of the conventional sensing disk coverage for target. The notion of information coverage is based on estimation theory to exploit the collaborative nature of geographically distributed sensors. Due to the use of information coverage, a target that is not within the sensing disk of any single sensor can still be considered to be monitored (information covered) by the cooperation of more than one sensor. This change of the problem settings complicates the solutions compared to that by using a disk coverage model. We first define the target information coverage (TIC) problem and prove its NP‐completeness. We then propose a heuristic to approximately solve our problem. Simulation results show that our heuristic is better than an existing algorithm and is close to the upper bound when only the sensing disk coverage model is used. Furthermore, simulation results also show that the network lifetime can be significantly improved by using the notion of information coverage compared with that by using the conventional definition of sensing disk coverage. Copyright © 2008 John Wiley & Sons, Ltd.     

人工神经网络在航迹关联中的应用研究

在分布式多传感器系统中的多节点情况下,航迹关联问题可以转化为多维分配问题。而多维分配问题是典型的组合优化问题,很难找到问题的最优解,而且其计算量随着问题规模的增加易出现指数爆炸现象。该文提出了一种三维神经网络模型,用以解决三节点情况下航迹关联的三维分配问题,并进行了实验仿真。仿真结果表明,三维人工神经劂络模型能够有效地求解此三维分配问题,并且具有较高的航迹关联正确率。另外三维神经网络模型同样可以推广到多维,用以解决航迹关联的多维分配问题。     

Finite-difference frequency-domain algorithm for modeling guided-wave properties of substrate integrated waveguide

In multilayer microwave integrated circuits such as low-temperature co-fired ceramics or multilayered printed circuit boards, waveguide-like structures can be fabricated by using periodic metallic via-holes referred to as substrate integrated waveguide (SIW). Such SIW structures can largely preserve the advantages of conventional rectangular waveguides such as high-Q factor and high power capacity. However, they are subject to leakage due to periodic gaps, which potentially results in wave attenuation. Therefore, such a guided-wave modeling problem becomes a very complicated complex eigenvalue problem. Since the SIW are bilaterally unbounded, absorbing boundary conditions should be deployed in numerical algorithms. This often leads to a difficult complex root-extracting problem of a transcend equation. In this paper, we present a novel finite-difference frequency-domain algorithm with a perfectly matched layer and Floquet's theorem for the analysis of SIW guided-wave problems. In this scheme, the problem is converted into a generalized matrix eigenvalue problem and finally transformed to a standard matrix eigenvalue problem that can be solved with efficient subroutines available. This approach has been validated by experiment.