3,922 Works

A Performance-efficient and practical processor error recovery framework

Jyothish Soman
Continued reduction in the size of a transistor has affected the reliability of processors built using them. This is primarily due to factors such as inaccuracies while manufacturing, as well as non-ideal operating conditions, causing transistors to slow down consistently, eventually leading to permanent breakdown and erroneous operation of the processor. Permanent transistor breakdown, or faults, can occur at any point in time in the processor’s lifetime. Errors are the discrepancies in the output of...

Pulse-based, on-chip interconnect

Simon J. Hollis
This thesis describes the development of an on-chip point-to-point link, with particular emphasis on the reduction of its global metal area footprint. To reduce its metal footprint, the interconnect uses a serial transmission approach. 8-bit data is sent using just two wires, through a pulse-based technique, inspired by the GasP interconnect from Sun Microsystems. Data and control signals are transmitted bi-directionally on a wire using this double-edged, pulse-based signalling protocol, and formatted using a variant...

Preconditions on geometrically sensitive subdivision schemes

Neil A. Dodgson, Malcolm A. Sabin & Richard Southern
Our objective is to create subdivision schemes with limit surfaces which are surfaces useful in engineering (spheres, cylinders, cones etc.) without resorting to special cases. The basic idea explored by us previously in the curve case is that if the property that all vertices lie on an object of the required class can be preserved through the subdivision refinement, it will be preserved into the limit surface also. The next obvious step was to try...

A marriage of rely/guarantee and separation logic

Viktor Vafeiadis & Matthew Parkinson
In the quest for tractable methods for reasoning about concurrent algorithms both rely/guarantee logic and separation logic have made great advances. They both seek to tame, or control, the complexity of concurrent interactions, but neither is the ultimate approach. Rely-guarantee copes naturally with interference, but its specifications are complex because they describe the entire state. Conversely separation logic has difficulty dealing with interference, but its specifications are simpler because they describe only the relevant state...

Efficient maximum-likelihood decoding of spherical lattice codes

Karen Su, Inaki Berenguer, Ian J. Wassell & Xiaodong Wang
A new framework for efficient and exact Maximum-Likelihood (ML) decoding of spherical lattice codes is developed. It employs a double-tree structure: The first is that which underlies established tree-search decoders; the second plays the crucial role of guiding the primary search by specifying admissible candidates and is our focus in this report. Lattice codes have long been of interest due to their rich structure, leading to numerous decoding algorithms for unbounded lattices, as well as...

Removing polar rendering artifacts in subdivision surfaces

Ursula H. Augsdörfer, Neil A. Dodgson & Malcolm A. Sabin
There is a belief that subdivision schemes require the subdominant eigenvalue, λ, to be the same around extraordinary vertices as in the regular regions of the mesh. This belief is owing to the polar rendering artifacts which occur around extraordinary points when λ is significantly larger than in the regular regions. By constraining the tuning of subdivision schemes to solutions which fulfill this condition we may prevent ourselves from finding the optimal limit surface. We...

Automatic classification of eventual failure detectors

Piotr Zieliński
Eventual failure detectors, such as Ω or ♢P, can make arbitrarily many mistakes before they start providing correct information. This paper shows that any detector implementable in an purely asynchronous system can be implemented as a function of only the order of most-recently heard-from processes. The finiteness of this representation means that eventual failure detectors can be enumerated and their relative strengths tested automatically. The results for systems with two and three processes are presented....

Parameterized complexity of distances to sparse graph classes

Jannis Bulian
This dissertation offers contributions to the area of parameterized complexity theory, which studies the complexity of computational problems in a multivariate framework. We demonstrate that for graph problems, many popular parameters can be understood as distances that measure how far a graph is from belonging to a class of sparse graphs. We introduce the term distance parameter for such parameters and demonstrate their value in several ways. The parameter tree-depth is uncovered as a distance...

A framework to build bespoke auto-tuners with structured Bayesian optimisation

Valentin Dalibard
Due to their complexity, modern computer systems expose many configuration parameters which users must manually tune to maximise the performance of their applications. To relieve users of this burden, auto-tuning has emerged as an alternative in which a black-box optimiser iteratively evaluates configurations to find efficient ones. A popular auto-tuning technique is Bayesian optimisation, which uses the results to incrementally build a probabilistic model of the impact of the parameters on performance. This allows the...

Signal maps for smartphone localisation

Chao Gao
Indoor positioning has been an active research area for 20 years. Systems based on dedicated infrastructure such as ultrasound or ultra-wideband (UWB) radio can provide centimetre-accuracy. But they are generally prohibitively expensive to build, deploy and maintain. Today, signal fingerprinting-based indoor positioning techniques, which use existing wireless infrastructure, are arguably the most prevalent. The fingerprinting-based positioning system matches the current signal observations (fingerprints) at a device to position it on a pre-defined fingerprint map. The...

Pipelined image processing for pattern recognition

A. Daniel Hall
Image processing for pattern recognition is both computationally intensive and algorithmically complex. The objective of the research presented here was to produce a fast inexpensive image processor for pattern recognition. This objective has been achieved by separating the computationally intensive pixel processing tasks from the algorithmically complex feature processing tasks. The context for this work is explored in terms of image processor architecture, intermediate-level image processing tasks and pattern recognition. A new language to describe...

Fixed point promotion: taking the induction out of automated induction

William Sonnex
This thesis describes the implementation of Elea: the first automated theorem prover for properties of observational approximation between terms in a functional programming language. A term approximates another if no program context can tell them apart, except that the approximating term can be less defined than the approximated term. Elea can prove terms equivalent by proving approximation in both directions. The language Elea proves approximations over is pure, call-by-name, and with non-strict data-types, a subset...

Deep embodiment: grounding semantics in perceptual modalities

Douwe Kiela
Multi-modal distributional semantic models address the fact that text-based semantic models, which represent word meanings as a distribution over other words, suffer from the grounding problem. This thesis advances the field of multi-modal semantics in two directions. First, it shows that transferred convolutional neural network representations outperform the traditional bag of visual words method for obtaining visual features. It is then shown that these representations may be applied successfully to various natural language processing tasks....

Artificial error generation for translation-based grammatical error correction

Mariano Felice
Automated grammatical error correction for language learners has attracted a lot of attention in recent years, especially after a number of shared tasks that have encouraged research in the area. Treating the problem as a translation task from ‘incorrect’ into ‘correct’ English using statistical machine translation has emerged as a state-of-the-art approach but it requires vast amounts of corrected parallel data to produce useful results. Because manual annotation of incorrect text is laborious and expensive,...

A formal hardware verification methodology and its application to a network interface chip

M.J.C. Gordon & J. Herbert
We describe how the functional correctness of a circuit design can be verified by machine checked formal proof. The proof system used is LCF_LSM [1], a version of Milner’s LCF [2] with a different logical calculus called LSM. We give a tutorial introduction to LSM in the paper. Our main example is the ECL chip of the Cambridge Fast Ring (CFR) [3]. Although the ECL chip is quite simple (about 360 gates) it is nevertheless...

Automated design of an instruction set for BCPL

J.P. Bennett

Category theory and models for parallel computation

Glynn Winskel
This report will illustrate two uses of category theory: Firstly the use of category theory to define semantics in a particular model. How semantic constructions can often be seen as categorical ones, and, in particular, how parallel compositions are derived from a categorical product and a nun-deterministic sum. These categorical notions can provide a basis for reasoning about computations and will be illustrated for the model of Petri nets. Secondly, the use of category theory...

Making form follow function
An exercise in functional programming style

Jon Fairbairn
The combined use of user-defined infix operators and higher order functions allows the programmer to invent new control structures tailored to a particular problem area. This paper is to suggest that such a combination has beneficial effects on the ease of both writing and reading programmes, and hence can increase programmer productivity. As an example, a parser for a simple language is presented in this style. It is hoped that the presentation will be palatable...

Planning multisentential English text using communicative acts

Mark Thomas Maybury
The goal of this research is to develop explanation presentation mechanisms for knowledge based systems which enable them to define domain terminology and concepts, narrate events, elucidate plans, processes, or propositions and argue to support a claim or advocate action. This requires the development of devices which select, structure, order and then linguistically realize explanation content as coherent and cohesive English text. With the goal of identifying generic explanation presentation strategies, a wide range of...

MCPL programming manual

Martin Richards
MCPL is a systems programming language having much in common with BCPL but augmented by the pattern matching ideas of both ML and Prolog. Unlike ML, MCPL is typeless, runs using a contiguous runtime stack and has no built in garbage collector, but it does make extensive use of ML-like pattern matching. The low level aspects of the language resemble those of BCPL and C. For efficiency, MCPL uses its own function calling sequence, however...

Term assignment for intuitionistic linear logic (preliminary report)

Nick Benton, Gavin Bierman & Valeria de Paiva
In this paper we consider the problem of deriving a term assignment system for Girard’s Intuitionistic Linear Logic for both the sequent calculus and natural deduction proof systems. Our system differs from previous calculi (e.g. that of Abramsky) and has two important properties which they lack. These are the substitution property (the set of valid deductions is closed under substitution) and subject reduction (reduction on terms is well typed). We define a simple (but more...

On efficiency in theorem provers which fully expand proofs into primitive inferences

Richard J. Boulton
Theorem Provers which fully expand proofs into applications of primitive inference rules can be made highly secure, but have been criticized for being orders of magnitude slower than many other theorem provers. We argue that much of this relative inefficiency is due to the way proof procedures are typically written and not all is inherent in the way the systems work. We support this claim by considering a proof procedure for linear arithmetic. We show...

On the calculation of explicit polymetres

W.F. Clocksin
Computer scientists take an interest in objects or events which can be counted, grouped, timed and synchronised. The computational problems involved with the interpretation and notation of musical rhythm are therefore of particular interest, as the most complex time-stamped structures yet devised by humankind are to be found in music notation. These problems are brought into focus when considering explicit polymetric notation, which is the concurrent use of different time signatures in music notation. While...

Retrieving spoken documents: VMR Project experiments

K. Spärck Jones, G.J.F. Jones, J.T. Foote & S.J. Young

Seven more myths of formal methods

Jonathan P. Bowen & Michael G. Hinchey

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