赋值:物理对象上的操作(英文)

研究了命令式程序的形式语义。赋值被看成当作物理对象的变量上的操作。变量x一方面是个可以容纳数据值的物理对象,另一方面当它出现在数学表达式中时又代表它所容纳的值。作为物理对象,变量x允许它的值用读/写操作来观察或改变,读操作则是写操作的逆操作。事实上赋值就是对物理对象施加写操作。提出了与单变量赋值、多重赋值、顺序赋值及条件赋值等相对应的操作,提出了这些操作应服从的公理,并给出了用这些公理证明程序性质的实例。     

C语言的使用技巧

在进行C语言的程序设计中,如何发现错误,如何快速准确地改正错误,如何编写尽可能少的错误代码的程序等问题一直是程序设计者希望解决的问题。笔者在进行C语言的程序设计和讲授C语言程序设计课程及指导学生上机实习时积累了一定的经验,在此介绍如下,供读者参考。 一、赋值号与等号的区别 在有的高级语言如BASIC中,赋值号与等号的符号一致,熟悉这些语言的程序设计     

对基于定义域的PROLOG进行编译

本文讨论把逻辑程序设计语言PROLOG编译成过程性高级语言的目标程序的问题。特别地,我们主张,把一致化操作编译成赋值语句,条件语句和分情形语句,这要求在编译时做源程序的全局性分析以预示“数据流”走向。     

如何正确使用ORACLE的Pro*C中的动态定义方法四

目前国内各种ORACLE参考资料对动态定义方法四的阐述皆不清楚明了,没有指出不存在赋值变量时动态定义方法四的简化用法,例子中的重要参考也是错误的。本文给出了正确使用方法四的步骤,给出了不存在赋值变量时的简化用法,通过例行程序指正了参考资料中的参数错误。所有这些也适用于其它宿主语言程序。     

Verilog HDL阻塞属性探究及其应用

阻塞赋值与非阻塞赋值语句作为verilog HDL语言的最大难点之一,一直困扰着FPGA设计者,而其中的错误又隐晦莫测,理解不透彻会直接导致运用不当,使设计工程达不到预期效果,而排错又相当麻烦.阻塞赋值与非阻塞赋值语句既血脉相连,又有本质的区别.透过原理和实际应用.从不同侧面对阻塞赋值与非阻塞赋值进行剖析,并阐述了阻塞赋值与非阻塞赋值的各自特点及其应用.     

基于层次化事件队列的赋值操作应用

随着ASIC、SoC和FPGA在工业生产和科研工作中的广泛应用, 作为硬件描述语言的Verilog HDL已成为实现集成电路设计的重要方式, 而设计师对其中赋值操作的错误使用, 也导致了部分设计的不正确。因此, 对于Verilog HDL中赋值操作的深入了解也成为解决设计中隐藏问题的瓶颈。基于层次化事件队列, 对设计中经常遇到的赋值操作问题进行了深入剖析, 并结合工作实际给出了避免设计中竞争问题出现的方法。     

游标在Oracle PRO*C中的使用方法及技巧

PL/SQL语言一般局限于对数据库的操作，本身不是计算完备的语言，如在变量类型上不仅高级程序设计语言(如：C语言)有如数组、指针等一些复杂交量类型；另外该语言是面向集合的语言(set-oriented languase)，即执行一条语句可以一次性地提供所需的所有元组，可是在实际编程时我们需要对这些元组逐个地赋值给相关变量，根据条件分别处理。目前解决此类问题办法是将PL／SQL语言嵌入到高级程序设计语言中，利用高级程序设计语言处理数据能力强的优点，与PL/SQL语言对数据库直接操作的特点相结合，共同完成，这在一定程度上，既增加编写程序的难度，又使整个程序繁琐。下面我向大家介绍在ORACLE数据库中，增加的工具游标，使用它可以方便地实现将多行查询结果进行逐行处理。     

785FORTRAN

<正> 785 FORTRAN是785计算机的一个向量语言系统。它允许把整个数组(或子数组)作为运算对象,把表达式扩充为数组表达式,把赋值句扩充为数组赋值句。用户使用这些语句成份即可编出得以在785机上高效运行的并行计算程序。 785 FORTRAN处理系统兼备有数组运算识别功能。它能够把古典的FORTRAN程序改造成合有尽可能多的数组运算的785 FORTRAN程序。 785 FORTRAN语言是ANSI FORTRAN 77的扩充。它的数组运算成份和     

一种用于类C语言环境的安全的类型化内存模型

使用形式化方法对程序进行验证是保证软件可信的重要手段.对于像C语言这样的较低级的命令式语言可以直接对内存进行操作,对其操作语义或公理语义的形式化需要基于合适的内存模型.传统的字节内存模型可以很好地描述各种内存操作,但是无法保证安全性,同时使程序验证变得异常复杂.面向对象语言的内存模型则具有较高的抽象性,便于程序验证,但不适合描述低级的内存操作.结合字节内存模型和面向对象语言内存模型,提出一种安全的类型化的内存模型,既可用于对语义的形式化,也可用于基于霍尔逻辑的程序验证.此内存模型既允许指针算术、结构赋值、类型转换等内存操作,同时也可以有效减少因指针别名给程序验证带来的复杂度.基于Coq辅助定理证明工具,对内存模型进行了形式化实现和验证.     

取值于赋值幺半群的加权正则文法语言

正则文法是研究自动机的重要工具。引入取值于赋值幺半群的加权正则文法、加权类正则文法的定义,讨论了赋值幺半群上加权正则文法、加权类正则文法和加权有限自动机(WFA)的关系。证明了在赋值幺半群上,已知一个加权正则文法或加权类正则文法,分别存在一个WFA与之等价。定义了可分配的赋值幺半群,证明了在可分配的赋值幺半群上已知一个WFA,存在一个加权正则文法和加权类正则文法与之等价,即证明了可分配的赋值幺半群上加权正则文法、加权类正则文法和WFA在生成语言上等价,并举例说明了赋值幺半群的可分配性不是已知WFA存在与之等价的加权正则文法或加权类正则文法的必要条件。     

Machine assignment and part-families formation using group technology

The conventional way of solving the group technology (GT) problem is to start from an assignment of parts to machines and try to find a partitioning of machine cells and part families. The similarity between parts is measured based on commonality of the machines assigned to them. However, parts are assigned to machines based on their operation requirements and the operation capabilities of machines. Similarity between parts should be based on their required operations. In this paper, the authors attempt to solve or facilitate solving the GT problem at the assignment level. An algorithm for assigning parts to machines is provided which utilizes the types of operations required by parts and applies GT principles in producing the assignment. This leads to better partitioning of machine cells and part-families. Furthermore, operation sequences required by parts in determining the similarity between parts have been considered. An algorithm to form part-families based on the operation sequence similarity coefficient has been developed. The resulting families are then used by the assignment algorithm to produce machine assignments to part-families. The use of the algorithm is demonstrated by examples.     

Optimizing vote and quorum assignments for reading and writingreplicated data

In the weighted voting protocol which is used to maintain the consistency of replicated data, the availability of the data to ready and write operations not only depends on the availability of the nodes storing the data but also on the vote and quorum assignments used. The authors consider the problem of determining the vote and quorum assignments that yield the best performance in a distributed system where node availabilities can be different and the mix of the read and write operations is arbitrary. The optimal vote and quorum assignments depend not only on the system parameters, such as node availability and operation mix, but also on the performance measure. The authors present an enumeration algorithm that can be used to find the vote and quorum assignments that need to be considered for achieving optimal performance. When the performance measure is data availability, an analytical method is derived to evaluate it for any vote and quorum assignment. This method and the enumeration algorithm are used to find the optimal vote and quorum assignment for several systems. The enumeration algorithm can also be used to obtain the optimal performance when other measures are considered     

An enriched model for the integrated berth allocation and quay crane assignment problem

Given the increasing pressure to improve the efficiency of container terminals, a lot of research efforts have been devoted to optimizing container terminal operations. Most papers deal with either the berth allocation problem (BAP) or the (quay) crane assignment problem (CAP). In the literature on the BAP, handling times are often simplified to be berth dependent or proportional to vessel size, so the CAP can be ignored when scheduling vessels. This is unsatisfactory for real-life applications because the handling time primarily depends on the number of containers to be handled and the number of cranes deployed. Only a limited number of papers deals with the combination of berth allocation and crane assignment. In these papers however, authors often have resorted to algorithmic simplifications that limit the practical use of the models. This paper presents a MILP model for the integrated BAP–CAP taking into account vessel priorities, preferred berthing locations and handling time considerations. The model is used in a hybrid heuristic solution procedure that is validated on real-life data illustrating the potential to support operational and tactical decision-making.     

非方阵指派问题的求解

本文将2 类方阵指派问题——极大极小和总体极小指派问题——的矩阵作业解法推广到非方阵情形, 即求解任务与人员数目不等的指派问题,且维持矩阵作业法的效率．假定m > n,则按本文行优先选取算法求解 m￡n 非方阵指派问题的最大逻辑运算量为O(mn2),其效率通常与执行一轮覆盖的矩阵作业法相当．     

Network Design Model to Integrate Shelter Assignment with Contraflow Operations in Emergency Evacuation Planning

Networks and Spatial Economics - In traditional emergency evacuation planning, shelter assignment and contraflow operations are determined sequentially. In this paper, we show that these two types...     

Operations Management of Distribution Centers for Vegetables and Fruits

We present a tactical decision model that improves the effectiveness of the operations of a distribution center for vegetables and fruits. The operations are complicated in the case of vegetables and fruits due to the seasonal fluctuations in production and demand and the need for special storage conditions for different products. Using the decision model we determine an assignment plan, based on historical data. The assignment plan is used at the operational level for storage advice. We used local search techniques to find an assignment plan. The effect of the assignment plan on several storage policies was examined with a simulation model of the operations in the distribution center. The developed model and algorithms are integrated in a PC-based decision support system.     

Including scalars in a programming language based on the relationalalgebra

Scalars, arrays, and records, together with associated operations and syntax, have been introduced as special cases of relations into the relational programming system, relix. This permits all of these data types, as well as relations, to be stored persistently. The requirement in most languages that array elements and record fields can be assigned to leads in this case to the general implementation of QT-selectors as l-expressions, with, in particular, systematic interpretations of assignment to projections and selections of relations. The authors discuss the principles and the implementation of this extension to the relational algebra. They take advantage of the very specialized syntax of array access to build a tuned access method, using B-trees and Z-order. The performance results show the advantage of this implementation over the slower implementation required for general QT-selectors     

On the variable-depth-search heuristic for the linear-cost generalized assignment problem

The classical assignment problem seeks to determine a mapping between a set of assignees and a set of assignments. The linear cost assignment problem (LCGAP), as a generalized model, incorporates the relative workloads between assignees and assignments. Although LCGAP is computationally intractable, it has been extensively studied because of its practical implications in many real world situations. Variable-depth-search heuristic (VDSH) method is one of the solution methods that have been developed to produce quality near-optimal solutions to LCGAP. The main structure of VDSH consists of two basic operations: reassign and swap. In this paper, we make further observations on this effective heuristic method through a series of computational experiments. The numerical results statistically evince that different combina-tions of these two operations will result in solutions of different quality levels. These findings are expected to have similar implications to search heuristics for other optimization problems.     

两种不同前提下的多电压调度对比

高层次综合中的多电压调度问题一般基于2个不同的前提：功能单元电压的静态配置和动态配置．这2个前提对操作的调度和电压分配有不同的影响，导致最终能工作在低电压的操作个数不同．对于这2个多电压调度问题分别提出了整数线性规划描述，并结合线性松弛的方法对这2种情况下工作在低电压的最大操作个数进行了测试和对比．最后，基于实验数据分析总结了两者的比值随时间约束和资源约束的变化情况．     

An expert system methodology for aircraft-gate assignment

The aircraft-gate assignment problem is a significant concern in airline operations. This paper addresses the use of knowledge based expert systems to help solve the aircraft-gate assignment problem. The problem is described and the factors that need to be considered in aircraft-gate assignment are identified and delineated. The expert system's architecture is presented and its working is described.