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London SW7 2BZ.
No full textThe Event Calculus of Kowalski and Sergot only deals with discrete change. This paper introduces a simplified version of the Event Calculus and extends it to deal with continuous change, as in the height of a falling object or the level of liquid in a filling vessel. The idea of autotermination is introduced. A period of continuous change autoterminates if it brings about the event which terminates it. For example, when the increasing level of water in a sink reaches the overflow, it ceases to increase. The formulation is applied to a simple example with liquid filling a sink, and to a more complicated one with many tanks discharging liquid into another tank. In Proceedings ECAI 90, pages 598-60
Iterated deferred correction for linear two-point boundary value problems
No full textAn analysis of iterated deferred correction based on various classes of implicit Runge-Kutta formulae is given. Out of different possibilities considered, it is shown that those based purely on Lobatto formulae have the best stability. The enhanced stability of Lobatto schemes is very important for the efficient integration of excessively stiff boundary value problems and this is demonstrated by means of some numerical results.UNIV LONDON IMPERIAL COLL SCI TECHNOL & MED, DEPT MATH, LONDON SW7 2BZ, ENGLANDUNESP, IBILCE, DEPT CIENCIAS COMP & ESTATIST, BR-15054000 S J RIO PRETO, SP, BRAZILUNESP, IBILCE, DEPT CIENCIAS COMP & ESTATIST, BR-15054000 S J RIO PRETO, SP, BRAZI
On The Phase of Least-Asymmetric Scaling and Wavelet Filters
No full textWhen using the discrete wavelet transform it is important that the filters at each scale are suitably shifted so that energy in the output sequence is appropriately positioned. We derive the form of the advance to apply to Daubechies' least-asymmetric scaling and wavelet filters at each scale, in order to obtain nearest to zero phase. At each scale the appropriate advance depends on whether half the length of each of the original quadrature mirror filters is even or odd. The departures from zero phase of the appropriately shifted wavelet filters are illustrated. The conditions under which the phase of appropriately shifted scaling and wavelet filters is continuous across octave bands (i.e., across scales) is investigated; the shifts derived here give rise to continuous phase functions. E.J. McCoy and A.T. Walden are with the Dept. of Mathematics, Imperial College of Science, Technology and Medicine, 180 Queen's Gate, London SW7 2BZ, U.K. D.B. Percival is with the Applied Physics Lab, U..
On The Phase of Least-Asymmetric Scaling and Wavelet Filters
No full textWhen using the discrete wavelet transform it is important that the filters at each scale are suitably shifted so that energy in the output sequence is appropriately positioned. We derive the form of the advance to apply to Daubechies' least-asymmetric scaling and wavelet filters at each scale, in order to obtain nearest to zero phase. At each scale the appropriate advance depends on whether half the length of each of the original quadrature mirror filters is even or odd. The departures from zero phase of the appropriately shifted wavelet filters are illustrated. The conditions under which the phase of appropriately shifted scaling and wavelet filters is continuous across octave bands (i.e., across scales) is investigated; the shifts derived here give rise to continuous phase functions. E.J. McCoy and A.T. Walden are with the Dept. of Mathematics, Imperial College of Science, Technology and Medicine, 180 Queen's Gate, London SW7 2BZ, U.K. D.B. Percival is with the Applied Physics Lab, U..
Angel: A Proposed Multiprocessor Operating System Kernel (Extended Abstract)
No full text) T.Wilkinson, T.Stiemerling and P.Osmon Computer Science Department, City University, Northampton Square, London EC1V 0HB, UK. & A.Saulsbury and P.Kelly Department of Computing, Imperial College, 180 Queens Gate, London SW7 2BZ, UK. 1 Introduction We describe an experimental multiprocessor operating system called Angel. The design of Angel builds on experience gained from constructing the Meshix operating system [1] and from the implementation of a distributed shared memory server on this system [2]. The aim is for Angel to support a single uniform shared memory address space on a multiprocessor machine which contains both shared and distributed memory. Such a machine is seen to be a hierarchical system containing multiprocessor clusters using physically shared memory, which are then loosely coupled using a multi-path network. A number of current operating systems have a micro-kernel implementation and support lightweight threads, examples being Mach [3] and Chorus [4]. In these syst..
Static Analysis of Value-Passing Process Calculi (Extended Abstract)
No full text) DAVID CLARK, LINDSAY ERRINGTON and CHRIS HANKIN Department of Computing, Imperial College 180 Queen's Gate, London SW7 2BZ, United Kingdom E-mail: fdjc2, le, [email protected] ABSTRACT Standard approaches to providing a semantics for value passing process calculi involve an expansion into a basic calculus which only involves pure synchronisation. When the semantics is intended to provide a basis for static analysis of properties of the values, this expansion leads to an unacceptable loss of information. In this paper we present a model of value passing process calculi based on synchronisation trees which gives a direct treatment of value passing. We present an abstract interpretation which discovers the same information about programs as Schreiber's flow analysis. 1 Introduction Schreiber has examined the problems of specifying and implementing communications protocols, using the value passing version of Milner's Calculus of Communicating Systems (CCS) to do both [7]. The syntacti..
Conditional exponential moments for iterated Wiener integrals
No full textWe provide sharp exponential moment bounds for (Stratonovich) iterated stochastic integrals under conditioning by certain small balls, including balls in certain Holder-like norms of exponent greater than 1=3. The proof uses a control of the variation of the L'evy area, under conditioning. The results are applied to the computation of the Onsager-Machlup functional of diffusion processes with constant diffusion matrix. Key Words: Iterated Wiener integrals. L'evy area. Onsager-Machlup functional. AMS (1991) subject classifications: 60H05, 60H10, 60J60. 1 Department of Mathematics, Imperial College, 180 Queen's gate, London SW7 2BZ, England. 2 Department of Electrical Engineering, Technion- Israel Institute of Technology, Haifa 32000, ISRAEL. Partially supported by a US-Israel BSF grant. 1 Introduction Throughout this paper, fXg denotes a canonical, IR d valued Brownian motion on C 0 i [0; 1]; IR d j and P denotes Wiener measure. The r-th (Stratonovich) iterated integral of ..
Complexity Spaces Revisited (Extended Abstract)
No full text) M. Schellekens Imperial College Department of Computing 180 Queen's Gate, London SW7 2BZ, UK E-mail: [email protected] Abstract The complexity (quasi-pseudo-metric) spaces have been introduced as part of the development of a topological foundation for the complexity analysis of algorithms ([Sch95]). Applications of this theory to the complexity analysis of Divide & Conquer algorithms have been discussed in [Sch95]. Typically these applications involve fixed point arguments based on the Smyth completion. The notion of S-completability plays an important role in the study of the complexity spaces since it implies a simplification of the Smyth completion to the bicompletion (e.g. [Sch95], [Smy92] and [Sun91]). A characterization of S-completable quasi-uniform spaces has been given in [Sun91]. We present a related characterization of S-completable quasi-pseudo-metric spaces and provide a simplified proof of the fact that weightable quasi-pseudo-metric spaces are S-completable ([Kun93])...
Polymorphic Intersection Type Assignment for Rewrite Systems with Abstraction and beta-rule (Extended Abstract)
No full textion and fi-rule Extended Abstract Steffen van Bakel 1 , Franco Barbanera 2 , and Maribel Fernandez 3 1 Department of Computing, Imperial College, 180 Queens Gate, London SW7 2BZ, [email protected] 2 Dipartimento di Matematica, Universita degli Studi di Catania, Viale A. Doria 6, 95125 Catania, Italia. [email protected]. 3 LIENS (CNRS URA 1327), Ecole Normale Superieure, 45, rue d'Ulm, 75005 Paris, France, [email protected] Abstract. We define two type assignment systems for first-order rewriting extended with application, -abstraction, and fi-reduction (TRS+ fi). The types used in these systems are a combination of (!-free) intersection and polymorphic types. The first system is the general one, for which we prove a subject reduction theorem and show that all typeable terms are strongly normalisable. The second is a decidable subsystem of the first, by restricting types to Rank 2. For this system we define, using an extended notion of unification, a notion of principal type,..
REACTIVE PASCAL and the Event Calculus: A platform to program reactive, rational agents
No full textJacinto A. D'avila Quintero [email protected] Logic Programming Section Department of Computing. Imperial College 180 Queen's Gate. London. SW7 2BZ. UK http://laotzu.doc.ic.ac.uk Phone: 0171-5948232 Fax: 0171-5891552 Abstract This paper describes a language to program an "intelligent" (reactive, rational) agent as that described by Kowalski in [5]. The new programming language, called REACTIVE PASCAL, is part of a specification platform that can be based on either the Situation Calculus [9] or the Event Calculus [7]. Some mechanisms for common-sense reasoning are, therefore, directly available. The programmer/designer can complete a background theory describing the relevant dynamics of the universe in which the agent will operate. The Elevator example is borrowed from [8] to illustrate the expressiveness of the platform. The combination of REACTIVE PASCAL programs and a background theory then enables the agent to perform temporal reasoning such as that required for planning. ..
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