Separate Compilation of Polychronous Specifications

As code generation for synchronous programs requires strong safety properties to be satisfied, compositionality becomes a difficult goal to achieve. Most synchronous languages, such as Esterel, Lustre or Signal require a given module or compilation unit to be insensitive to latency that communication with its environment may incur. In Lustre or Signal, for instance, a compilation unit must satisfy the so-called property of endochrony. To preserve endochrony in an asynchronous environment, an ad-hoc protocol is synthesized to interface the module. However, endochrony is not preserved by composition. Consequently, the protocol has to be rebuilt every time a new module is added in the environment. We propose a methodology and code generation scheme which simplifies this concern. It consists of weakening the global objective of globally preserving endochrony. Instead, we aim at the preservation of a more liberal and compositional objective, weak endochrony [D. Potop-Butucaru and B. Caillaud and A. Benveniste. Concurrency in Synchronous Systems. In Formal Methods in System Design, v. 28(2). Springer, March 2006], which is compositional and much closer from the expected requirement of insensitivity to communication latency. As a result, our code generation scheme supports true separate compilation: a locally compiled synchronous module does not require its synthesized interface with the environment to be rebuilt once composed with another module.     

On Development of Iterative Programs from Function Specifications

A systematic approach to the development of totally correct iterative programs is investigated for the class of accumulation problems. In these problems, the required output information is usually obtained by accumulation during successive passes over input data structures. The development of iterative programs for accumulation problems is shown to involve successive generalizations of the data domain and the corresponding function specifications. The problem of locating these generalizations is discussed. It is shown that not all function specifications can be realized in terms of terminating computations of a stand-alone iterative program. A linear data domain is defined in terms of decomposition and finiteness axioms, and the property of well behavedness of a loop body over a linear data domain is introduced. It is shown that this property can be used to generate loop body specifications from specifically chosen examples of program behavior. An abstract program for an accumulation problem is developed using these considerations. The role of generalizations as an added parameter to the program development process is discussed.     

Refinement and Development of Programs from Relational Specifications

These tutorial notes present an overview of specification and refinement concepts and methods that are based on relations.     

Compilation of Constraint Programs with Noncyclic and Cyclic Dependencies to Procedural Parallel Programs

This paper reports on a compiler for translation of constraint specifications into procedural parallel programs. A constraint program in our system consists of a set of constraints and an input set containing a subset of the variables appearing in the constraints. The compiler described in this paper successfully compiles a substantially larger class of constraint specifications to efficient programs than did its predecessors. In particular the compiler has been extended to generate processor and memory efficient programs for cyclic constraints which can be resolved by computational relaxation methods. The paper first details the basic compilation process for noncyclic constraints. It then describes the additional steps in the compilation process which enable resolution of cyclic constraints to iterative computational processes and illustrates the process using derivation of a parallel program for solution of the Laplace equation as the example.     

Efficient Execution of Pure Object-Oriented Programs by Follow-up Compilation

Dynamic type checking and method binding slows pure object-oriented programs such as those written in Smalltalk. Dynamic method lookup is needed to support method overriding and type-method conformance. We have developed a platform independent technique that implements method overriding efficiently for pure object-oriented languages. The technique involves binding non-overridden method calls at compile time. The overridden method calls are also resolved (and bound) statically using simple inferences. Overridden method bindings are corrected dynamically using an Overridden Method Dictionary. Using simulations, we demonstrate that this technique offers 35% –70% reduction in the average method lookup delay over the Berkeley Smalltalk implementation. This technique has very low compile time overhead, memory overhead, does not need specialized hardware and allows shared code pages in concurrent programs. For programs which may be re-used, it is proper to have a follow-up compilation to generate efficient code after the program development is complete. Received November 7, 2001; revised March 27, 2002 Published online: October 24, 2002     

Functional Differentiation of Computer Programs

We present a purely functional implementation of the computational differentiation tools—the well known numeric (i.e., not symbolic) techniques which permit one to compute point-wise derivatives of functions defined by computer programs economically and exactly (with machine precision). We show how the use of lazy evaluation permits a transparent and elegant construction of the entire infinite tower of derivatives of higher order for any expressions present in the program. The formalism may be useful in various problems of scientific computing which often demand a hard and ungracious human preprocessing before writing the final code. Some concrete examples are given.     

方志索引的计算机辅助编制

本文提出了一种索引系统的计算机实现方法。基于此方法利用Delphi设计了一种方志索引系统。实践证明可以节省大量的人力,并保证输出结果的准确性和信息的完整性。     

计算机取证及其规范论述

从上世纪八十年代开始,人们就在研究将计算机应用于取证,发展至今,在计算机取证的思想、理论和方法等 方面都已经取得了重大的突破。本文在该背景之下对计算机取证及其规范进行了论述。在对计算机取证的概念进行详细介 绍的基础上,提出目前计算机取证所面临的问题以及相应的解决措施,对我国在应用计算机取证方面的规范加以完善。     

基于局域网的计算机病毒预防方案设计

随着计算机和因特网的日益普及,计算机病毒的危害性越来越大。在与计算机病毒的对抗中,为了减少损失,应该以“预防为主,防治结合”的方针进行实施。计算机病毒的预防要有方案设计才能保证其实效性。本文提出了一种预防方案,可以有效防止计算机病毒,尤其是蠕虫病毒和ARP病毒的侵入。     

Construction of Interactive Programs in Computer Graphics

In interactive computer graphics, one often finds a gap between sophisticated algorithms, using very high level data structures, and poor methods of program and object construction. Particular programming languages are too readily adopted for solving problems, before a precise specification of the problem to be solved has been formulated.
This paper shows that progress can be made by using modern engineering methods to specify and develop graphical software. Two programming techniques are studied here: the algebraic specification of data types and a functional static modular method of problem statement.
The paper also discusses these proposals in the context of other modes of computer graphics specification and programming.     

Compilation and Communication Strategies for Out-of-Core Programs on Distributed Memory Machines

It is widely acknowledged that improving parallel I/O performance is critical for widespread adoption of high performance computing. In this paper, we show that communication in out-of-core distributed memory problems may require both interprocessor communication and file I/O. Thus, in order to improve I/O performance, it is necessary to minimize the I/O costs associated with a communication step. We present three methods for performing communication in out-of-core distributed memory problems. The first method, called thegeneralized collective communicationmethod, follows a loosely synchronous model; computation and communication phases are clearly separated, and communication requires permutation of data in files. The second method, called thereceiver-driven in-core communication, communicates only the in-core data. The third method, called theowner-driven in-core communication, goes even one step further and tries to identify the potential future use of data (by the recipients) while it is in the senders memory. We provide performance results for two out-of-core applications: the two-dimensional FFT code, and the two-dimensional elliptic Jacobi solver.     

The Specialist's Role in Computer Training Programs

Without realizing it, many organizations offer their employees the same old computer training programs that no longer provide the knowledge today's computer users need to make the most efficient use of their systems. This column suggests one simple change to current training programs—namely sending the teachers (specialists) out of the computer classroom and to the students (users)—which can increase the users' confidence in the system and make them more productive.     

The Specialist's Role in Computer Training Programs

Without realizing it, many organizations offer their employees the same old computer training programs that no longer provide the knowledge today's computer users need to make the most efficient use of their systems. This column suggests one simple change to current training programs—namely sending the teachers (specialists) out of the computer classroom and to the students (users)—which can increase the users' confidence in the system and make them more productive.     

国内外土壤质地自动分类程序介绍

土壤质地是反映土壤物理特性的一个综合指标,土壤质地命名的自动化将有效提高土壤质地分类工作的效率。本文结合土壤质地自动分类程序研究的现状与特点,着重阐述并讨论了目前较为成熟的TAL、TRANGLE和STAC自动分类计算机程序的设计、功能、使用和实例及其异同与优缺点。土壤质地命名的应用试验表明:TAL和TRANGLE程序在批处理数据量、分类制、图形显示、统计功能等方面存在局限,STAC程序则相对较为完善、方便、实用。     

Casting Petri Nets into Programs

A programming system has been implemented in which annotated Petri nets are used as machine-processable high-evel design representations. The nets can be used to express the parallelism and the dynamic sequential dependencies found in complex software. They can then be interactively fired to facilitate debugging of the design. The nets are processed into a procedure language, called XL/1, to which a variety of transformations are applied in order to produce more efficient programs. These programs are generated for either a serial or a parallel processing environment. Finally, the XL/1 programs may be translated into PL/I or PL/S. The serial processing versions have been compiled and run successfully, but the parallel processing versions have not yet been run in a parallel processing environment.     

用C语言编写二个通用计算程序

在中学数学教学内容中,应用一元二次方程求根公式计算一元二次方程的根和应用高斯主元素消去法计算线性方程组的解是一部分具有机械计算性的程式化的单元,这使得很适合用C语言编写其计算程序.按照结构化思路设计编写C程序的二个实例.     

Computer Society Offers Full Slate of Programs in 2006

To promote the active exchange of information, ideas, and technological innovation, the IEEE Computer Society sponsors a full spectrum of conferences, publications, local and student chapters, a distance learning campus, and numerous technical committees and standards working groups.     

On the Uncertainty in the Correctness of Computer Programs

The use of digital computers in critical process control systems requires the formal assessment of the system reliability. Failures can be due to either component malfunctions or design faults. Only the latter are relevant in evaluating software reliability. Although it is preferable to prove whether the program meets its specification, this is not yet practical for real-time control programs. Further, the specification itself can be incorrect or incomplete due to the complex requirements.     

编程题的计算机阅卷

分析了当前的一些计算机考试系统的特点,指出了其存在的不足之处。为了更加合理和有效地使用计算机进行阅卷,首先提出了几个新概念,然后在此基础上给出了一个编程题的计算机阅卷模式,对其实现流程进行了详细的阐述,最后对结果进行了分析。该系统已经用于实际的教学环节中,收到了良好的效果。