Software measurement: Problems and practice

Software measurement is a key element in the evolving software engineering discipline. This paper seeks to identify some of the principal problems surrounding the measurement process and the metrics themselves. Metrics are shown in various modeling contexts. Measures of static software complexity are explored together with measures of dynamic program complexity. These data are then used to identify regions of software that are fault prone. This information is then exploited to develop a model of dynamic program complexity for the identification of failure prone software. Empirical experiences with the practice of measurement from an ongoing research project on the Space Shuttle Primary Avionics Software System are employed to augment the discussion.     

Detecting directed 4-cycles still faster

We present a method to detect simple cycles of length 4 of a directed graph in O(n^1/ωe^2−2/ω) steps, where n denotes the number of nodes, e denotes the number of edges and ω is the exponent of matrix multiplication. This improves upon the currently fastest methods for α∈(2/(4−ω),(ω+1)/2), where e=n^α.     

基于FCE方法的超声速机翼厚度分布优化

远场组元(Far-field Composite Element,FCE)激波阻力优化方法是基于类别形状函数变换(Class Shape Transformation,CST)参数化方法发展出的一种超声速飞行器气动外形优化方法。文章使用CST参数化方法对超声速客机的大后掠机翼进行外形参数化,并以机翼容积和局部相对厚度为约束条件,使用FCE方法对其厚度分布进行以激波阻力最小为设计目标的快速优化。与原机翼相比,FCE优化方法使机翼激波阻力系数降低达61%,是超声速飞行器概念设计阶段降低激波阻力十分有用的优化方法。     

求解RANS方程的高阶间断Galerkin方法研究

基于二维结构网格,对间断Galerkin方法(DGM)求解雷诺平均Navier-Stokes(RANS)方程进行了研究。根据混合有限元方法的思想,引入辅助变量,对粘性项中的高阶导数项进行降阶处理,再应用DGM对辅助变量方程和降阶后的RANS方程进行联立求解。对平板层流流动进行了数值模拟,结果表明,随着逼近多项式次数的增加,速度型和摩擦系数更加接近Blasius解。此外,还引入了Bald-win-Lomax湍流模型,对NACA0012翼型跨音速粘性流场进行了数值模拟,与实验结果进行了对比,进一步验证了算法的可靠性。     

噪声空间谱预白化小孔径阵列被动目标检测方法

为了解决小孔径阵列在低信噪比下不能正确检测被动目标的问题,提出了两种小孔径阵列非白噪声场空间预白化方法:噪声空间谱模值归一化(MNNSS)和噪声协方差矩阵求逆(NCMI)方法。假设噪声场为空间平稳非白噪声场,通过学习得到平稳非白噪声场的空间角谱和噪声协方差矩阵,使用学习的空间角谱和协方差矩阵对阵列接收数据进行预白化处理。将预白化处理后的阵列数据用于空间谱检测器。水池实验数据处理结果表明,采用MNNSS和NCMI方法对阵列接收数据预白化处理可明显改善小孔径阵列噪声场的非白特性,预白化处理后空间谱检测器在检测概率达到90%时的可检测信噪比分别下降了3 dB和7 dB;MNNSS和NCMI方法运算量不大,可以运用到实时处理系统。     

单机有界分批排序

本文研究了当所有工件同时到达且工期相同时的单机有界分批排序问题,给出了求解加权总误工数∑WJUJ问题的多项式时间算法．     

一种迭代求解离散对数的Pohlig-Hellman算法

针对Pohlig-Hellman类算法中需要存储每一个基数下的同余数的不足,提出一种利用迭代法直接计算离散对数的方法。该方法不再需要对每一个基数下的同余数进行存储,节约了一定存储空间。同时,利用穷尽搜索法代替Shank算法的调用,时间复杂度有所降低。理论研究和数字分析表明,改进算法具有较好的计算能力。     

异构STAP系统的多层次数据通信研究

空时自适应处理(STAP)系统的实现,包括系统任务分配、海量数据的通信和存储,算法模块的并行、映射和调度.针对数据通信在实时系统中是不同节点间的多层次、多速率数据传输的问题,在建立的参数化处理模型基础上,研究了异构STAP系统实现中的不同任务间通信规划方法,讨论了不同通信结构层次对数据通信的影响,并基于粗粒度任务模型实现了四通道STAP系统.实验结果表明,规划的数据通信方案能满足系统的实时处理要求.     

Bounds on the sizes of irredundant test sets and sequences for combinational logic networks

We present a method of determining lower and upper bounds on the number of tests required to detect all detectable faults in combinational logic networks. The networks are composed of AND, OR, NAND, NOR, and XOR gates. The fault model assumes that single stuck-at-zero faults occur on the lines of the networks, with the additional requirement that XOR gates be tested with all possible input combinations. The goal is to provide a simple and efficient implementation that processes the fanout-free subnetworks separately, and then combines the results without the need to consider the effects of reconvergent fanout. We introduce the concepts of irredundant test sets, where no test can be deleted regardless of the order of test application, and irredundant test sequences, where every test detects at least one additional fault when tests are applied in order. Identifying and differentiating between these types of collections of tests allows us to understand more precisely the mechanisms and expected performance of test generation and test compaction methods. We apply our test counting technique and two other published procedures to a set of benchmark circuits. Our bounds are shown to compare favorably to the results obtained by the other published approaches. We obtain minimal and maximal test sets and test sequences using a greedy optimization technique. Our bounds are shown to produce tight bounds for the smaller circuits; they grow more conservative as the size of the circuits increase.     

Improved upper complexity bounds for the discrete fourier transform

The linear complexityL ₂ (G) of a finite groupG is the minimal number of additions, subtractions and multiplications by complex constants of absolute value 2 sufficient to evaluate a suitable Fourier transform of G. Combining and modifying several classical FFT-algorithms, we show thatL ₂(G)8|G|log₂|G| for any finite metabelian groupG.