A Framework for Simple Sorting Algorithms on Parallel Disk Systems

In this paper we present a simple parallel sorting algorithm and illustrate its application in general sorting, disk sorting, and hypercube sorting. The algorithm (called the (l,m) -mergesort (LMM)) is an extension of the bitonic and odd—even mergesorts. Literature on parallel sorting is abundant. Many of the algorithms proposed, though being theoretically important, may not perform satisfactorily in practice owing to large constants in their time bounds. The algorithm presented in this paper has the potential of being practical. We present an application to the parallel disk sorting problem. The algorithm is asymptotically optimal (assuming that N is a polynomial in M , where N is the number of records to be sorted and M is the internal memory size). The underlying constant is very small. This algorithm performs better than the disk-striped mergesort (DSM) algorithm when the number of disks is large. Our implementation is as simple as that of DSM (requiring no fancy data structures or prefetch techniques.) As a second application, we prove that we can get a sparse enumeration sort on the hypercube that is simpler than that of the classical algorithm of Nassimi and Sahni [16]. We also show that Leighton's columnsort algorithm is a special case of LMM. Online publication December 26, 2000.     

一种基于PVM的Multisets并行归并算法

Multisets排序是指对具有k个不同计算机系统、基于消息传递环境下,以加法运算为基础的稳定的归并并行算法,该算法实现对Multisets的排序,其时间复杂度为O(n/p log p k log p 4p n/2).     

A Tree-based Mergesort

We demonstrate that if standard Mergesort is implemented using finger search trees instead of arrays it optimally adapts to a set of measures of presortedness not fulfilled by any other algorithm. Received: 7 October 1993 / 18 July 1996     

Optimal Read-Once Parallel Disk Scheduling

An optimal prefetching and I/O scheduling algorithm L-OPT, for parallel I/O systems, using a read-once model of block references is presented. The algorithm uses knowledge of the next $L$ references, $L$-block lookahead, to create a minimal-length I/O schedule. For a system with $D$ disks and a buffer of capacity $m$ blocks, we show that the competitive ratio of L-OPT is $\Theta(\sqrt{mD/L})$ when $L \geq m$, which matches the lower bound of any prefetching algorithm with $L$-block lookahead. Tight bounds for the remaining ranges of lookahead are also presented. In addition we show that L-OPT is the optimal offline algorithm: when the lookahead consists of the entire reference string, it performs the absolute minimum possible number of I/Os. Finally, we show that L-OPT is comparable with the best online algorithm with the same amount of lookahead; the ratio of the length of its schedule to the length of the optimal schedule is always within a constant factor.     

一个简单有效的口令识别方案

基于口令的身份识别技术是分布式网络环境中使用最为广泛的一种技术，然而传统的口令识别技术容易受到字典攻击、重传攻击和拒绝服务攻击。针对Sandirigara等人提出的SAS协议，提出了一种简单有效的口令识别方案SEPA，该方案可以抵御字典攻击、重传攻击和服务器拒绝服务攻击，且计算负荷和通信负荷较小。     

Selection Algorithms for Parallel Disk Systems

With the widening gap between processor speeds and disk access speeds, the I/O bottleneck has become critical. Parallel disk systems have been introduced to alleviate this bottleneck. In this paper we present deterministic and randomized selection algorithms for parallel disk systems. The algorithms to be presented, in addition to being asymptotically optimal, have small underlying constants in their time bounds and hence have the potential of being practical.     

A Simple and Efficient Randomized Byzantine Agreement Algorithm

A new randomized Byzantine agreement algorithm is presented. This algorithm operates in a synchronous system of n processors, at most t of which can fail. The algorithm reaches agreement in 0(t/log n) expected rounds and O(n2tf/log n) expected message bits independent of the distribution of processor failures. This performance is further improved to a constant expected number of rounds and O(n2) message bits if the distribution of processor failures is assumed to be uniform. In either event, the algorithm improves on the known lower bound on rounds for deterministic algorithms. Some other advantages of the algorithm are that it requires no cryptographic techniques, that the amount of local computation is small, and that the expected number of random bits used per processor is only one. It is argued that in many practical applications of Byzantine agreement, the randomized algorithm of this paper achieves superior performance.     

一种简单高效的密封式电子拍卖方案

针对目前大多数的电子拍卖方案都是假设存在一个可信第三方,使得电子拍卖的安全性有所降低的问题,提出一个基于不可信第三方的密封式电子拍卖方案。采用数字签名技术对竞拍者的身份进行验证,确保竞拍者身份的隐私性。在计算成交价时,基于离散对数求解的困难性,对竞拍价的二进制长度进行加密封装,保证竞拍价的秘密性以及结果的正确性。分析结果证明,该方案设计简单,安全性较高,在计算效率上相对于现有多数电子拍卖方案有较大的提高。     

一种基于并口的简易虚拟示波器

一种基于微机标准外部接口——并口通信并采用外置式结构的简易虚拟示波器的设计和实现。     

一种简单高效的移动agent控制机制

移动agent的控制机制包括移动agent的定位、终止和孤儿检测机制,该机制在移动agent系统中起着非常重要的作用。目前对agent的各种定位机制研究较多,对后两种机制研究较少,因此当前的移动agent系统大多不具备孤儿检测的能力。本文在分析研究各种控制机制的基础上,指出现有的能量机制和影子机制实现孤儿检测能力所面临的问题,而后提出了一种利用权值和路径代理机制相结合的移动agent控制机制,该机制不仅能定位移动agent的位置,而且还能有效地检测和处理在网络某结点的孤儿agent,也能根据需要终止移动agent的执行,从而能及时有效地回收被无用agent占用的软硬件资源,同时还避免了能量和影子机制的缺点,是一种较理想的控制机制。另外,该机制还具有实现简单、灵活性强等优势。     

一种简单快速的车牌定位算法

车牌定位是汽车牌照识别系统的关键技术之一。通过对图像进行预处理,去除干扰的噪声,然后利用隔行扫描和矩形窗口搜索法来定位车牌的上下边界和左右边界,从而提高了车牌定位的速度。提出了利用车牌定位出来的区域面积的变化情况来判断车牌的倾斜情况,并对倾斜的车牌进行了准确的校正。实验结果表明,该算法简单高效。     

一种简单有效的无线信道仿真方法及应用

产生统计独立的多径衰落信道是无线信道仿真的一个基本问题.针对B3G-TDD系统中的频率选择性衰落信道提出了一种简单有效的仿真方法.该方法基于瑞利衰落信道的波普和比利(Pop and Beaulieu)模型建立,通过引入衰落指针,使多个瑞利衰落信道彼此独立,并为每个瑞利衰落信道分配不同的时延.仿真结果表明,设计出的频率选择性衰落信道不仅简单而且符合信道特点.运用该方法研究了BPSK信号通过瑞利衰落信道和频率选择性衰落信道以后的误码率情况并进行了比较,提出正交频分复用技术作为改善信道衰落的有效方法.B3G-TDD系统中信道估计的实验结果表明,这种方法是高效而且可行的.     

Simple and Efficient Minimal RDFS

The original RDFS language design includes several features that hinder the task of developers and theoreticians. This paper has two main contributions in the direction of simplifying the language. First, it introduces a small fragment which, preserving the normative semantics and the core functionalities, avoids the complexities of the original specification, and captures the main semantic functionalities of RDFS. Second, it introduces a minimalist deduction system over this fragment, which by avoiding certain rare cases, obtains a simple deductive system and a computationally efficient entailment checking.     

Processor Efficient Parallel Matching

In this paper we consider the problem of finding perfect matchings in parallel. We present a RNC algorithm with almost optimal work with respect to sequential algorithms, i.e., it uses O(n ^ω ) processors, where ω is the matrix multiplication exponent. Our algorithm is based on an RNC algorithm for computing determinant of a degree one polynomial matrix which is of independent interest. Research supported by KBN grant 1P03A01830.     

EED: Energy Efficient Disk drive architecture

Energy efficiency has become one of the most important challenges in designing future computing systems, and the storage system is one of the largest energy consumers within them. This paper proposes an Energy Efficient Disk (EED) drive architecture which integrates a relatively small-sized NAND flash memory into a traditional disk drive to explore the impact of the flash memory on the performance and energy consumption of the disk. The EED monitors data access patterns and moves the frequently accessed data from the magnetic disk to the flash memory. Due to the data migration, most of the data accesses can be satisfied with the flash memory, which extends the idle period of the disk drive and enables the disk drive to stay in a low power state for an extended period of time. Because flash memory consumes considerably less energy and the read access is much faster than a magnetic disk, the EED can save significant amounts of energy while reducing the average response time. Real trace driven simulations are employed to validate the proposed disk drive architecture. An energy coefficient, which is the product of the average response time and the average energy consumption, is proposed as a performance metric to measure the EED. The simulation results, along with the energy coefficient, show that the EED can achieve an 89.11% energy consumption reduction and a 2.04% average response time reduction with cello99 trace, a 7.5% energy consumption reduction and a 45.15% average response time reduction with cello96 trace, and a 20.06% energy consumption reduction and a 6.02% average response time reduction with TPC-D trace, respectively. Traditionally, energy conservation and performance improvement are contradictory. The EED strikes a good balance between conserving energy and improving performance.     

Proof Pearl—A Mechanized Proof of GHC’s Mergesort

We present our Isabelle/HOL formalization of GHC’s sorting algorithm for lists, proving its correctness and stability. This constitutes another example of applying a state-of-the-art proof assistant to real-world code. Furthermore, it allows users to take advantage of the formalized algorithm in generated code.     

一个简单高效的动态手势识别方法

文章首先给出了基于角度的动力学模型及其特征值,并提出了基于SCG神经网络的静态特征值识别算法和基于模板匹配的动态特征值识别算法。使用该文提出的动态时间规整算法和手势分割算法建立的动态手势识别系统,实践证明具有较好的实时性和识别率。     

一种基于自更新的简单高效Cache一致性协议

随着片上多处理器系统核数的增加,当前一致性协议上存在的许多问题使共享存储系统复杂而低效.目前一些一致性协议极其复杂,例如MESI(modified exclusive shared or invalid)协议,存在众多的中间状态和竞争.并且这些协议还会导致额外失效通信,以及大量记录共享信息的目录存储开销(目录协议)或广播消息的网络开销(监听协议).对数据无竞争的程序实现了一种简单高效一致性协议VISU(valid/invalid states based on self-updating),这种协议基于自更新操作(self-updating)、只包含2个稳定状态(valid/invalid).所设计的两状态VISU协议消除了目录和间接事务.首先基于并行编程的数据无竞争(data race free, DRF)模型,采用在同步点进行自更新共享数据来保证正确性.其次利用动态识别私有和共享数据的技术,提出了对私有数据进行写回、对共享数据进行写直达的方案.对于私有数据,简单的写回策略能够简化不必要的片上通信.在L1 cache中,对于共享数据的写直达方式能确保LLC(last level cache)中数据最新从而消除了几乎所有的一致性状态.实现的VISU协议开销低、不需要目录、没有间接传输和众多的一致性状态,且更加容易验证,同时获得了与MESI目录协议几乎相当甚至更优的性能.