Restricted compositions and permutations: From old to new Gray codes

Any Gray code for a set of combinatorial objects defines a total order relation on this set: x is less than y if and only if y occurs after x in the Gray code list. Let ? denote the order relation induced by the classical Gray code for the product set (the natural extension of the Binary Reflected Gray Code to k-ary tuples). The restriction of ? to the set of compositions and bounded compositions gives known Gray codes for those sets. Here we show that ? restricted to the set of bounded compositions of an interval yields still a Gray code. An n-composition of an interval is an n-tuple of integers whose sum lies between two integers; and the set of bounded n-compositions of an interval simultaneously generalizes product set and compositions of an integer, and so ? put under a single roof all these Gray codes.As a byproduct we obtain Gray codes for permutations with a number of inversions lying between two integers, and with even/odd number of inversions or cycles. Such particular classes of permutations are used to solve some computational difficult problems.     

基于改进MC算法的医学图像三维重建研究

MC算法是经典的三维重建方法。但它重建时效率低,产生了大量的三角面片,增加了绘制的时间和空间。而且存在拓扑二义性,会使重建后的图像产生空洞的结构,重建的效果也不是很理想。对此,提出相应的改进策略。介绍了如何提高计算效率、减少三角面片数量、消除二义性和平滑图像等方面。通过实验证明了改进算法的可行性。     

基于像素链的直线绘制算法

针对直线生成算法在直线斜率大于0.5时的低效率问题,提出一种基于像素链的直线绘制算法。将直线看做是由许多条平行像素链或对角像素链拼接而成,提出并利用逆向生成直线的类Bresenham算法,将斜率在0.5~1的直线绘制转换为斜率在0~0.5的直线绘制,一次判断生成一条像素链。仿真实验表明,基于像素链的算法生成的直线与Bresenham算法生成直线一致,且计算量显著减少。该算法只有加法和乘法两种整数运算,适合硬件实现,其绘制速度是Bresenham算法的4倍。     

对C++中继承的二义性之探讨

讨论了Ｃ＋＋中的继承关系,阐述了类型的重要性,着重探讨继承所产的二义性问题。     

热轧实施计划中最优倒垛问题的整数规划模型及遗传算法

对钢铁企业板坯库中的最优倒垛问题建立了0和1整数规划模型.这一模型是一个 二次规划模型,且目标函数的系数与变量的取值相关联,属于NP-难问题,获得较大规模的最 优解是不可能或非常困难.为了求解此问题,本文构造了改进遗传算法:(1)提出了适合于最 优倒垛问题的遗传编码,运用此编码,不但能够产生可行的初始染色体,而且能够保证在交叉 和变异操作后的染色体仍然可行;(2)改进了遗传算法结构,在新的结构中,增加了一个培育 操作,改进了交叉操作.通过精选随机产生的问题例子的实验显示出,提出的算法的性能明显 好于原系统的启发式算法,最好的改进率达到7.04％.     

求补舍入并行和位长自适应整数转浮点数电路设计

提出了一种实现整数转浮点数的新的设计方法 ,并且对方法的正确性给予了证明 .采用这种设计方法 ,实现了求补和舍入的合并并行 ,使关键路径的延时比常规的电路设计方案减少了 15级门 ,同时降低了电路规模 .关键路径延时的减小 ,使这一转换可以在单周期内完成 .另外 ,该方法实现了位长自适应 ,只需花费很少的电路规模和延时实现控制 ,就可以适应长整型、整型到单、双精度浮点数的转换 ,增强了电路功能 .这一设计方法同样适用于其逆转换 .该转换模块采用 Fujitsu CE71库设计 ,在 10 0 MHz主频下经仿真验证 ,结果正确 ,已经应用到实际工程中 .     

基于H.264/AVC的帧内4×4预测模式快速选择算法

在H.264/AVC视频编解码标准中,帧内预测利用周围像素预测当前块来降低空间冗余,能极大地提高H.264/AVC的编码效率。然而,帧内预测的4×4预测有9种模式,为选出最佳模式,全搜索算法需要花费极大的计算量。为了降低帧内预测的复杂度,文章结合9种预测模式的各自特点和整数变换的线性性质,提出一种适用于H.264/AVC帧内4×4模式选择的快速变换和量化算法来减少对应模式变换和量化操作步骤的计算量。实验结果表明,优化算法可以有效地减少整数变换和量化操作的计算量。     

基于多品种生产的预制梁厂设计优化模型的研究

针对我国现阶段基于多品种生产的预制梁厂设计和排产传统方法的缺陷,通过对预制梁厂设计和生产影响因素的调查与分析,结合优化理论与方法,建立了基于多品种生产的预制梁台设计和预制梁厂排产优化模型,并进行了实例验证,将优化方法同传统算法相比较,证明优化模型具有明显的优势,能够较好地辅助施工单位进行预制梁厂设计和生产决策。     

A computational study on the quadratic knapsack problem with multiple constraints

The quadratic knapsack problem (QKP) has been the subject of considerable research in recent years. Despite notable advances in special purpose solution methodologies for QKP, this problem class remains very difficult to solve. With the exception of special cases, the state-of-the-art is limited to addressing problems of a few hundred variables and a single knapsack constraint.In this paper we provide a comparison of quadratic and linear representations of QKP based on test problems with multiple knapsack constraints and up to eight hundred variables. For the linear representations, three standard linearizations are investigated. Both the quadratic and linear models are solved by standard branch-and-cut optimizers available via CPLEX. Our results show that the linear models perform well on small problem instances but for larger problems the quadratic model outperforms the linear models tested both in terms of solution quality and solution time by a wide margin. Moreover, our results demonstrate that QKP instances larger than those previously addressed in the literature as well as instances with multiple constraints can be successfully and efficiently solved by branch and cut methodologies.     

Optimal cyclic single crane scheduling for two parallel train oilcan repairing lines

Crane is widely used to move a heavy object from one place to another not only in manufacturing industry but also service industry. As an important resource in the train oilcan repairing, crane scheduling affects directly the productivity of the systems. In this paper, we study cyclic single crane scheduling problem with two parallel train oilcan repairing lines, where jobs are loaded into the line at one end and unloaded at the other end. The processing time at each workstation must be within a given range. There is no buffer between these stations. A crane is used to move jobs between the workstations in two parallel lines. The objective is to schedule the moves to minimize the production cycle. We proposed a time way diagram for two parallel lines and developed a mixed integer linear programming model. Then we extended the model to the scheduling problem with multi-station to eliminate the bottleneck in lines. Examples are given to demonstrate the effectiveness of the model.