Showing papers in "CTIT technical reports series in 1996"

Measuring Bottleneck Link Speed in Packet-Switched Network

Abstract: Abstract The quality of available network connections can often have a large impact on the performance of distributed applications. For example, document transfer applications such as FTP, Gopher and the World Wide Web suffer increased response times as a result of network congestion. For these applications, the document transfer time is directly related to the available bandwidth of the connection. Available bandwidth depends on two things: 1) the underlying capacity of the path from client to server, which is limited by the bottleneck link; and 2) the amount of other traffic competing for links on the path. If measurements of these quantities were available to the application, the current utilization of connections could be calculated. Network utilization could then be used as a basis for selection from a set of alternative connections or servers, thus providing reduced response time. Such a dynamic server selection scheme would be especially important in a mobile computing environment in which the set of available servers is frequently changing. In order to provide these measurements at the application level, we introduce two tools: bprobe, which provides an estimate of the uncongested bandwidth of a path; and cprobe, which gives an estimate of the current congestion along a path. These two measures may be used in combination to provide the application with an estimate of available bandwidth between server and client thereby enabling application-level congestion avoidance. In this paper we discuss the design and implementation of our probe tools, specifically illustrating the techniques used to achieve accuracy and robustness. We present validation studies for both tools which demonstrate their reliability in the face of actual Internet conditions; and we give results of a survey of available bandwidth to a random set of WWW servers as a sample application of our probe technique. We conclude with descriptions of other applications of our measurement tools, several of which are currently under development.

Efficient estimation in semiparametric Garch models

Abstract: It is well-known that financial data sets exhibit conditional hereroskedasticity. GARCH-type models are often used to model this phenomenon. Since the distribution of the rescaled innovations is generally far from a normal distribution, a semiparametric approach is advisable. Several publications observed that adaptive estimation of the Euclidean parameters is not possible in the usual parametrization when the distribution of the rescaled innovations is the efficient score functions in the parametric model of the autoregression parameters are orthogonal to the tangent space generated by the nuisance parameter, thus suggesting that adaptive estimation of the autoregression parameters is possible. Indeed, we construct adaptive and hence efficient estimators in a general GARCH in mean-type context including integrated GARCH models. Our analysis is based on a general LAN theorem for time-series models, published elsewhere. In contrast to recent literature about ARCH models we do not need moment condition.

A general conservative extension theorem in process algebras with inequalities

Abstract: We prove a general conservative extension theorem for transition system based process theories with easy-to-check and reasonable conditions. The core of this result is another general theorem which gives sufficient conditions for a system of operational rules and an extension of it in order to ensure conservativity, that is, provable transitions from an original term in the extension are the same as in the original system. As a simple corollary of the conservative extension theorem we prove a completeness theorem. We also prove a general theorem giving sufficient conditions to reduce the question of ground confluence modulo some equations for a large term rewriting system associated with an equational process theory to a small term rewriting system under the condition that the large system is a conservative extension of the small one. We provide many applications to show that our results are useful. The applications include (but are not limited to) various real and discrete time settings in ACP, ATP, and CCS and the notions projection, renaming, stage operator, priority, recursion, the silent step, autonomous actions, the empty process, divergence, etc.

Core Technologies for System Renovation

Abstract: Renovation of business-critical software is becoming increasingly important. We identify fundamental notions and techniques to aid in system renovation and sketch some basic techniques: generic language technology to build analysis tools, a knowledge retrieval system to aid in program understanding, and a coordination architecture that is useful to restructure monolithic systems thus enabling their renovation. We argue that these techniques are not only essential for the renovation of old software but that they can also play an important role during the development and maintenance of new software systems.

Reverse Engineering and System Renovation: an Annotated Bibliography

Abstract: To facilitate research in the field of reverse engineering and system renovation we have compiled an annotated bibliography. We put the contributions not only in alphabetical order but also grouped by topic so that readers focusing on a certain topic can read their annotations in the alphabetical listing. We also compiled an annotated list of pointers to information about reverse engineering and system renovation that can be reached via Internet. For the sake of ease we also incorporated a brief introduction to the field of reverse engineering.

Data Flow Analysis for Reverse Engineering

Abstract: Cover picture: The oldest known depiction of juggling: a wall painting found in one of the crypts of the Beni Hassan tombs, dating from the middle kingdom of the ancient Egyptian civilization (between 1994 and 1781 B.C.). starting point of the project was the investigation and speciication of techniques to support data ow analysis for reverse engineering and program understanding. I would like to thank Prof. dr. P. Klint who introduced me to the project, and gave me a lot of freedom in doing things as I thought best. The members of the Programming Research Group, especially dr. M.G.J. van den Brand and dr. C. Verhoef, supported me on various aspects of my work and make a nice environment to work in. Paul Klint, Chris Verhoef, Mark van den Brand and Arie van Deursen read draft versions of this document and gave many useful remarks to improve its readability. Finally, Ivonne, my parents, friends, and the members of the Department of Pure Juggling provided all kinds of useful distraction at times when I needed it most.

The Iterative Solution of Fully Implicit Discretizations of Three-Dimensional Transport Models

Abstract: We investigate the use of approximate factorization and diagonalizing techniques for solving iteratively fully implicit numerical models of three-dimensional transport-chemistry problems. In particular, we investigate various possibilities that can take advantage of the parallelization and vectorization facilities offered by parallel vector computers.

Specifying Input and Output of Visual Languages

Abstract: We consider \\context free\" speciication of visual syntax { with the aid of visual (i.e., 2-dimensional and user-deened) \\lexicals\". We argue that context-free visual syntax speciication can go a long way towards speciication of visual languages in the presence of certain intelligent tools. We focus on the input and output behavior of visual languages in demonstrating this point. The usual notion of term construction in a editor is extended by allowing sharing of sub-terms. We demonstrate the utility of this for constructing input terms (programs) of visual languages. We also allow such sharing of sub-terms in equations editors which are used to specify language semantics. This sharing not only allows the building of appropriate (visual) terms but also provides information on the desired view of an output term. We introduce a technique called \\Share-Where\" which is used to preserve layout information and demonstrate its use as well as its limitations. We then describe an extension to our formalism which allows dynamic input and output { interaction during term execution. We demonstrate this with a full example for the FSA language to animate FSA term evaluation.

ANSI Cobol III in SDF + an ASF Definition of a Y2K Tool

Abstract: COBOL programs are heavily used in business applications. With the arrival of the year 2000, companies using large software systems, often based on (some dialect of) COBOL, are facing serious problems. A formal speci cation of the COBOL language can perhaps assist in solving these problems. This thesis gives an overview of the ANSI standard de nition of COBOL III, presents an algebraic speci cation of the syntax of COBOL III, and describes its speci cation process. Furthermore, it introduces a year 2000 reverse engineering tool based on PICTURE clauses. Finally, it discusses related work (including a di erent approach to specifying COBOL), and gives suggestions for future work.

An efficient algorithm for minimum-weight bibranching

Abstract: Given a directed graphD=(V,A) and a setS?V, a bibranching is a set of arcsB?Athat contains av?(V\S) path for everyv?Sand anS?vpath for everyv?V\S. In this paper, we describe a primal?dual algorithm that determines a minimum weight bibranching in a weighted digraph. It has running timeO(n?(m+nlogn)), wherem=|A|,n=|V| andn?=min{|S|,|V\S|}. Thus, our algorithm obtains the best known bounds for two important special cases of the problem: bipartite edge cover andr-branching.

Embedded system simulation: testdriving the ToolBus

Abstract: We have investigated the use of the ToolBus application architectureeBK95] for the development of embedded system simulators. We developed a exible and intuitive simulator, stable enough to be used in a commercial setting, with an execution speed comparable to that of the simulated hardware. This extensible simulator is based on a loosely coupled set of tools that form a framework for eecient construction of new simulators. Because this project is one of the rst serious applications of the ToolBus, we have also set out to gain experience with ToolBus programming in a project of substantial proportions.

A transformation tool for pure Prolog programs: the algebraic specification

Abstract: This technical report contains the complete annotated algebraic speciication of`TransLog', a transformation tool for pure Prolog programs. TransLog supports the interactive transformation of (a part of) a program by means of buttons representing transformation steps. As much as possible, pure Prolog semantics are preserved. The choice of pure Prolog semantics induces a number of conditions that have to be satissed before a particular transformation step is to be applied.

Quantum gravity slows inflation

Abstract: We consider the quantum gravitational back-reaction on an initially inflating, homogeneous and isotropic universe whose topology is T{sup 3} {times} {Re}. Although there is no secular effect at one loop, an explicit calculation shows that two-loop processes act to slow the rate of expansion by an amount which becomes non-pertubatively large at late times. By exploiting Feynman`s tree theorem we show that all higher loops act in the same sense. 18 refs., 1 fig.

The role of the endpoint in weighted polynomial approximation with varying weights

Abstract: For a weight functionw: [a, b]→(0, ∞), we consider weighted polynomials of the formwn Pn where the degree ofPn is at mostn. The class of functions that can be approximated with such polynomials depends on the behavior of the densityv(t) of the extremal measure associated withw. We show that every approximable function must vanish at the endpointa ifv(t) behaves like (t−a)β ast→a with β>−1/2. We also present an analogous result for internal points. Our results solve some open problems posed by V. Totik and disprove a conjecture of G.G. Lorentz on incomplete polynomials.

Transforming an ASF+SDF Specification into a ToolBus Application

Abstract: An algebraic speciication of the natural numbers is being translated into C code, such that the modular structure of the speciication is preserved. We use the ToolBus, a component interconnection architecture, to couple the resulting C programs. The result is a calculation tool, consisting of independent components, which can work with innnitely large (positive) integers without running into some maximum integer value. It supports diierent forms of representation of numbers in a exible way.

Solving type equations in multi-level specifications (preliminary version)

Abstract: In rst-order algebraic speciication functions have types of the form s1 sn ! s0, where the si are type constants. Such types exclude higher-order and polymorphic functions. In multi-level algebraic speci-cation the structure of types used in function declarations is speciied as an algebraic data type. If only free constructors are used in the types used in function declarations, type assignment is an extension of the Hind-ley/Milner algorithm to multiple levels of types. By means of equations over types, sophisticated type systems can be modeled in a simple and uniform language. The type assignment for arbitrary multi-level specii-cations requires E-uniication. Although this is undecidable in general, it is decidable for restricted sets of equations. In an earlier paper, the modular applicative multi-level equational speciication formalism MLS is deened. The typechecker supports only free type constructors. In this paper we introduce multi-level speciication by means of a series of MLS examples and discuss the extension with an E-uniication procedure instead of syntactic uniication of the type assignment function for MLS such that it supports type deenitions, deened type operators and recursive types.

A Correspondence between Nuprl and the Ramified Theory of Types

Abstract: In RusselPs Ramified Theory of Types RTT, two hierarchical concepts dominate: orders and types. The use of orders has as a consequence that the logic part of RTT is predicative. The concept of order however, is almost dead since Ramsey eliminated it from RTT. This is why we find Church's simple theory of types (which uses the type concept without the order one) at the bottom of the Barendregt Cube rather than RTT. Despite the disappearence of orders which have a strong correlation with predicativity, predicative logic still plays an influential role in Computer Science. An important example is the proof checker Nuprl, which is based on Martin-LoPs Type Theory which uses type universes. Those type universes, and also degrees of expressions in AUTHOMATH, are closely related to orders. In this paper, we concentrate on Nuprl. We describe Nuprl as a Pure Type System and relate it to Russell's RTT. To be successful at so doing, we are forced to explicitly typing Nuprl (but this is not restrictive). We show also that Russell's orders playa crucial role in understanding the hierarchy of Nuprl.

CWI contributions to the development of parallel Runge-Kutta methods

Abstract: textThis paper will concentrate on contributions of CWI to the development of parallel Runge-Kutta (RK) methods. We shall describe two approaches to construct such methods. In both approaches, a conventional implicit RK method is used as a corrector equation whose solution is approximated by an iterative method. In the first approach, the iteration method uses a fixed number of iterations without solving the corrector. Assuming that a one-step predictor is used, this approach again results in an RK method, however, an RK method possessing a lot of intrinsic parallelism. In the second approach, the corrector is solved by modified Newton iteration and the linear systems arising in each Newton iteration are solved by a parallel iteration process which is tuned to the special form of these linear systems. Furthermore, we apply the parallel iteration process in a step-parallel fashion which further enhances the amount of parallelism. Finally, the application of parallel RK methods within the framework of waveform relaxation is briefly discussed.

Multi-level specifications

Abstract: A list(A) (::) [] type prod (->) (#) list type (->) (#) type list A list(A)

Lunar Limb Observatory: An Incremental Plan for the Utilization, Exploration, and Settlement of the Moon

Abstract: This paper proposes a comprehensive incremental program, Lunar Limb Observatory (LLO), for a return to the Moon, beginning with robotic missions and ending with a permanent lunar settlement. Several recent technological developments make such a program both affordable and scientifically valuable: robotic telescopes, the Internet, light-weight telescopes, shared- autonomy/predictive graphics telerobotic devices, and optical interferometry systems. Reasons for focussing new NASA programs on the Moon include public interest, Moon-based astronomy, renewed lunar exploration, lunar resources (especially helium-3), technological stimulus, accessibility of the Moon (compared to any planet), and dispersal of the human species to counter predictable natural catastrophes, asteroidal or cometary impacts in particular. The proposed Lunar Limb Observatory would be located in the crater Riccioli, with auxiliary robotic telescopes in M. Smythii and at the North and South Poles. The first phase of the program, after site certification, would be a series of 5 Delta-launched telerobotic missions to Riccioli (or Grimaldi if Riccioli proves unsuitable), emplacing robotic telescopes and carrying out surface exploration. The next phase would be 7 Delta-launched telerobotic missions to M. Smythii (2 missions), the South Pole (3 missions), and the North Pole (2 missions), emplacing robotic telescopes to provide continuous all-sky coverage. Lunar base establishment would begin with two unmanned Shuttle/Fitan-Centaur missions to Riccioli, for shelter emplacement, followed by the first manned return, also using the Shuttle/Fitan-Centaur mode. The main LLO at Riccioli would then be permanently or periodically inhabited, for surface exploration, telerobotic rover and telescope operation and maintenance, and support of Earth-based student projects. The LLO would evolve into a permanent human settlement, serving, among other functions, as a test area and staging base for the exploration, settlement, and terraforming of Mars.

Transformations of Reduction Systems

Abstract: a b 0 b 1 b 2

Test set for IVP solvers

Abstract: In this paper a collection of Initial Value test Problems for systems of Ordinary Differential Equations, Implicit Differential Equations and Differential-Algebraic Equations is presented. This test set is maintained by the project group for Parallel IVP Solvers of CWI, department of Numerical Mathematics. This group invites everyone to contribute new test problems to this test set. How new problems can be submitted can be found in this paper as well.

Properties of the Task Allocation Problem

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Search and Imperative Programming

Abstract: We augment the expressive power of imperative programming in order to make it a more attractive vehicle for problems that involve search. The proposed additions are limited yet powerful and are inspired by the logic programming paradigm. We illustrate their use by presenting solutions to a number of classical problems, including the straight search problem, the knapsack problem, and the 8 queens problem. These solutions are substantially simpler than their counterparts written in the conventional way and can be used for different purposes without any modification.The proposed language is an intermediate stage on the road towards a realization of a strongly typed constraint programming language that combines the advantages of the logic programming and imperative programming.

Compact dynamisch busstation

Abstract: In opdracht van Nederland Haarlem hebben de Universiteit Utrecht (UU) en het Centrum voor Wiskunde en Informatica (CWI) een studie gemaakt naar het ontwerp van een Compact Dynamisch Busstation (CDB). Het betreft een regelsysteem voor het dynamisch toewijzen van bussen aan perrons, waarbij constant ingespeeld wordt op afwijkingen van de dienstregeling. Deze studie heeft geleid tot een model van een Compact Dynamisch Busstation; zodra er vertragingen optreden waardoor reserveringen van bussen met elkaar in conflict raken, wordt er met behulp van lineaire programmeringstechnieken een nieuwe optimale toewijzing opgesteld. Ook is er een zgn. prototype ontwikkeld, een software omgeving waarin dit model is uitgewerkt, zodat men zich ook een beeld kan vormen van het daadwerkelijk functioneren.