向量化友好的循环分块因子选择算法

具有病态规模的嵌套循环程序在进行循环分块时容易忽略分块因子对向量化的影响,导致非对齐数据访问,降低分块后循环代码的性能。提出了一种向量化友好的循环分块因子选择算法VEC-TSS。该算法对可向量化循环层以向量化收益分析确定分块因子,对其他循环层通过以局部性收益和并行粒度确定分块因子。实验结果表明,针对具有病态规模的循环程序,VEC-TSS算法与另外两种分块因子选择算法相比可以获得更好的程序加速比,同时具有良好的可扩展性。     

红黑Gauss-Seidel Stencil并行性和局部性优化

Stencil(模版计算)是一类常见的循环嵌套计算模式,被广泛应用于计算电磁、天气模拟、地球物理、海洋模拟等许多科学和工程模拟应用中.随着现代处理器体系结构的发展,多核和多层存储层次不断加深,研究并行性和局部性成为了提高程序运行速度的主要途径.分块是开发数据局部性和程序并行性的主要技术之一,目前,针对Stencil已提...     

基于神经网络模型的stencil循环最优分块大小预测

stencil循环是科学与工程计算应用中最主要的计算核心之一。循环分块技术可有效改善stencil循环的数据局部性,提高计算并行度。分块的大小选择对stencil循环的性能影响很大,传统的分块大小选择方法通常在时间开销、人工成本、分块选择精度等方面存在短板,实用性较差。文中提出了一种基于人工神经网络的分块大小选择方法,用于预测三维Jacobi型stencil循环程序的最优分块。对来源于实际数值模拟软件中的11个stencil循环进行最优分块预测,实验结果显示,在单核串行和多核并行两种场景下,程序使用模型预测分块相比不分块的性能提升分别为2%和35%,与网格搜索方法的分块性能相当,但在线预测时间开销仅约为后者的1/30 000。此外,相比基于静态分析的Turbo-tiling方法,预测最优分块的实测性能平均提升了约9%。     

面向规则DOACROSS循环的流水并行代码自动生成

发掘DOACROSS 循环中蕴含的并行性,选择合适的策略将其并行执行,对提升程序的并行性能非常重要.流水并行方式是规则DOACROSS 循环并行的重要方式.自动生成性能良好的流水并行代码是一项困难的工作,并行编译器对程序自动并行时常常对DOACROSS 循环作保守处理,损失了DOACROSS 循环包含的并行性,限制了程序的并行性能.针对上述问题,设计了一种选择计算划分循环层和循环分块层的启发式算法,给出了一个基于流水并行代价模型的循环分块大小计算公式,并使用计数信号量进行并行线程之间的同步,实现了基于OpenMP 的规则DOACROSS 循环流水并行代码的自动生成.通过对有限差分松弛法（finite difference relaxation,简称FDR）的波前（wavefront）循环和时域有限差分法（finite difference time domain,简称FDTD）中典型循环以及程序Poisson,LU 和Jacobi 的测试,算法自动生成的流水并行代码能够在多核处理器上获得明显的性能提升,使用的流水分块大小计算公式能够较为精确地计算出循环流水并行时的最佳分块大小.自动生成的流水并行代码与基于手工选择的最优分块大小的流水并行代码相比,加速比达到手工选择加速比的89%.     

基于空间密铺的并行Stencil算法

Stencil计算是一种科学和工程应用中常见的循环模式,而分块技术是一种提高数据局部性和并行性的强大转换方法。与以往直接对整个迭代空间进行分块的分块技术不同,提出了一种新的两层密铺分块的并行算法。首先,利用不同分块密铺数据空间;然后,所有分块沿时间维度扩展密铺迭代空间。该算法有以下优点:(1)最大化并发执行;(2)无冗余计算;(3)简洁的循环条件;(4)适应Stencil不同的尺寸、形状、阶数和边界条件。实验结果表明,对于3D27p Stencil,非周期边界的性能比Pluto高12%,周期边界的性能比Pochoir最高提升40%。     

编译器优化技术之Cache分块优化技术探讨

高速缓冲存储器（Cache）是高性能计算机的重要部件。循环分块是一种提高Cache命中率的技术,循环分块的大小是决定循环分块效率的关键因素。本文解释了cache失效的原因,并分析了如何有效地减少Cache的失效率。本文在分析处理器的特点的基础上,提出了“部分Cache局部性”[1]方法,实践表明,该方法有很好的优化效果,且易于实现。     

SAR成像并行仿真的访存局部性优化技术

合成孔径雷达SAR(Synthetic Aperture Radar)成像仿真对处理速度和存储空间都有很高的要求,因此基于并行计算平台的局部性优化技术成为了降低访存开销、提高SAR成像速度的关键技术之一。以典型SAR成像仿真程序——R-D程序为代表,研究SAR成像并行仿真中的访存局部性优化技术,重点根据循环变换和数据布局变换的局部性优化理论,提出对大规模SAR回波数据进行转置和分块的局部性优化技术。实验结果证明,经过访存局部性优化的SAR成像程序能够获得显著的性能提升。     

通过数组分块技术优化Cache性能

高速缓冲存储器（Cache）是高性能计算机的重要部件。循环分块是一种提高Cache命中率的技术。循环分块的大小是决定循环分块效率的关键因素。本文解释了cache失效的原因，并分析了如何有效地减少Cache的失效率。     

基于嵌套循环分类的并行识别技术

传统的分布存储并行编译系统大多是在共享存储并行编译系统的基础上开发的.共享存储并行编译系统的并行识别技术适合OpenMP代码生成,实现方式是将所有嵌套循环都按照相同的识别方法进行处理,用于分布存储并行编译系统必然会导致无法高效发掘程序的并行性.分布存储并行编译系统应根据嵌套循环结构的特点进行分类处理,提出适合MPI代码生成的并行识别技术.为解决上述问题,根据嵌套循环的结构和MPI并行程序的特点,提出了一种新的嵌套循环分类方法,并针对不同的嵌套循环分别提出了相应的并行识别技术.实验结果表明,与采用传统并行识别技术的分布存储并行编译系统相比,按照所提方法对嵌套循环进行分类,采用相应并行识别技术的编译系统能够更高效地识别基准程序中的并行循环,自动生成的MPI并行代码其性能加速比提高了20%以上.     

面向SW26010处理器的三维Stencil自适应分块参数算法

Stencil计算是科学应用中的一类重要计算,而分块是提升Stencil计算数据局部性的关键技术.针对现有三维Stencil优化在SW26010处理器上缺少时间分块以及分块参数需手工调优的问题,引入时间分块,提出了面向SW26010处理器的三维Stencil自适应分块参数算法.通过建立性能分析模型,结合硬件计算能力及存储容量等限制因素,文中系统地分析了分块参数对模型性能的影响,判断性能瓶颈,指导分块参数的优化方向.基于性能分析模型,自适应分块参数算法可给出预测性能最优时的分块参数,有利于三维Stencil在SW26010处理器上的快速优化部署.选取了三维7点和三维27点Stencil算例进行实验.与未使用时间分块的三维Stencil优化相比,以上两个算例在自适应选择的分块参数下可以达到1.47和1.29的加速比,且实际最优分块参数与理论最佳分块参数一致,这验证了所提性能分析模型及自适应分块参数算法的有效性.     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.