Cognitive Science attempts to study entities which in some sense possess beliefs, intentions, desires etc. The preferred term in this thesis for such entities is agents. An attempt at a scientific analysis of agents however throws up a number of questions. What are the right concepts to describe agents? What kinds of formal notations permit perspicuous reasoning about agents? What can be said about the architecture and construction of agents? The introductory section of this thesis discusses these questions in some detail, using Dennett's ideas about intentional systems [Den87] as a point of departure. I then examine a number of studies from Artificial Intelligence, Logic, Natural Language semantics and Philosophy which give shape to the current state of the art in agent theory. This leads to the development of a mathematical model of multi-object/agent interaction, which I call the SRS-model (SRS - Synchronous Reactive Systems). I demonstrate the adequacy of the model by using it to formalise learning and games scenarios. Next, various logics are introduced which capture input-output and then belief-desire level descriptions of agents. These logics are given an SRS-model semantics, and adequacy is shown by modelling a psychological experiment (an agent in a Skinner Box). It is shown how the example can be formally analysed in terms of mechanisms and architecture at the SRS-level (including a computer simulation); at the level of behaviourism (using a temporal logic - APTL); and at an intentional level (using an epistemic-conative temporal logic ECTL). Some remarks are made about extending the analysis to multi-agent situations involving co-operation, competition and dialogue. Finally, a detailed survey is made of the main mathematical and logical resources available to the style of formal cognitive science advocated in this thesis. I include modal logic, including its epistemic and doxastic variants; the extension of modal logic to dynamic logic; and the various approaches recently developed in the logic of time.

We propose a framework for the evaluation of implicitly parallel functional programs on message passing multiprocessors with special emphasis on the issue of load bounding. The model is based on a new encoding of the lambda-calculus in Milner's pi-calculus and combines lazy evaluation and eager (parallel) evaluation in the same framework. The pi-calculus encoding serves as the specification of a more concrete compilation scheme mapping a simple functional language into a message passing, parallel program. We show how and under which conditions we can guarantee successful load bounding based on this compilation scheme. Finally we discuss the architectural requirements for a machine to support our model efficiently and we present a simple RISC-style processor architecture which meets those criteria.

MPEG compressed video is very sensitive to data loss; not only may corruption caused by the loss of an ATM cell be quite severe, but the use of inter-frame predictive coding may cause the corruption to persist or even spread over a period of several frames. In order to lessen the impact of cell loss on compressed video, several people (for example; Ghanbari, Kishino et al.) have proposed techniques for splitting the coded bitstream into two layers of differing importance to the decoded video quality, and transmitting these layer at different cell loss priorities by utilising the ATM cell loss priority bit. The great improvements gained from the use of such layered coding and transmission schemes raise the question of how much further improvement might be gained if we had more ATM cell priority levels to use. This thesis presents an investigation into the performance benefits of MPEG video transmission over a hypothetical ATM network supporting four, as opposed to the standard two, priority levels. The investigation considers three prioritisation schemes: a simple un-layered method that prioritises cells based upon the estimated level or corruption within the decoded video that may occur as a result of losing each cell, a two layer coding scheme based upon the MPEG-2 data partitioning method, and an extension of the two layer scheme to use three layers. The performance for each of these coding and prioritisation methods is evaluated in terms of the decoded root mean square error (RMSE), by transmission over a simulated one, two and four priority level ATM network. The results appear to indicate that while prioritisation of an un-layered MPEG video cell stream using two priority levels is of some benefit, extending the scheme to utilise four priority levels is of only limited effectiveness. The layered coding results meanwhile show that the new low priority layers created by extending data partitioning beyond two layer coding are not of significantly different importance to the decoded RMSE video quality to warrant transmission at different priorities, and that for the systems tested, four priority levels would again offer only a modest improvement in performance over two priority levels. Subjective video quality evaluation tests however confirm a definite difference in subjective importance between the layers, and suggest a performance improvement for four priority level transmission.

Thesis (M.S.)--Boston University

Thesis (M.A.)--Boston University / A complex modern society has presented its managers with the need to solve a variety of optimization problems. The desire to run a firm in such a way that profit is maximized, to schedule bombing runs to inflict a maximum of damage on an opponent consistent with acceptable losses, or to choose an assignment of available personnel which optimizes efficiency are typical examples. Such problems are called programming problems. The unifying idea here is that the limited resources (e.g. factors of production, planes, or personnel) which are available for use may be combined in a large (generally infinite) number of ways. The object is to choose from these possibilities the combination or combinations which will optimize a measure of the effectiveness of the enterprise. Mathematically, the programming problem is stated. [TRUNCATED]

No description available.

Formex algebra is a powerful tool for the generation of data used in the design and analysis of space structures. However, for the algebra to be of practical use, it is necessary to have a means of employing the concepts on a computer. This is the particular problem which this thesis addresses. The solution proposed here is Formian, an interactive programming language, which being modelled on formex algebra allows complex configurations to be generated from a few concise and yet readily understood statements. Formian is designed to allow problems of data generation to be tackled in a single programming environment. The thesis describes the raison d'etre for the Formian programming language and the steps taken to create the language and to provide a practical and reliable implementation in the form of a computer program. A complete description of the language structure is given. This includes an overview of formex algebra. The use of Formian from a designer's viewpoint is provided by interspersing the description with practical examples.

This thesis documents the research; development methodology and evaluation of „Progranimate‟, a visual programming environment and associated pedagogy that helps novices overcome their difficulties in learning programming via an imperatives first (non object oriented) approach. In particular it focuses on problem solving and its prerequisite skills, these are known to be particularly troublesome for novice programmers. Progranimate is a unique, web deliverable, simplified development environment that utilises dynamic structured flowchart program construction, generated code in several selectable languages and animated execution. Progranimate uses a structured flowchart visualisation to convey the key concepts and underlying abstractions of programming, whilst allowing the novice to focus on the development of problem solving skills. Progranimate utilises an easy to use, uncluttered development environment and removes the necessity of writing complex code. This allows the user to focus solely on problem solving and on conceptualising the underlying abstractions and semantics of programming. In Progranimate, programs are constructed and executed visually via dynamic flowchart and code based representations. The visual synchronisation between the flowchart and code representations allow the user to draw an effective correlation between the flowchart and the logical code structure that it represents. Program animation features provide the user with an accurate mental model of program execution by emphasising the interaction and behaviour of the key structures and components used in programming. A variable inspection feature is also provided, allowing the user to observe the changes in data as a program is executed. Coupled to Progranimate is a scaffolding pedagogy designed to assist novice programmers in the development of problem solving skill. The pedagogy is underpinned by the theories of scaffolding support and the zone of proximal development. This pedagogy has been utilised within a range of contextual, fun, and gender neutral programming activities designed for use with Progranimate. This thesis hypothesises that using Progranimate on its own or with the scaffolding pedagogy for the creation of simple programs, will help novices strengthen their conceptual understanding of programming and problem solving skills. Evaluations of Progranimate with secondary schoolpupils, their teachers and first year university students support this hypothesis. The evaluations also show that Progranimate coupled to the scaffolding pedagogy and associated programming problems is a very motivating way to introduce secondary school pupils to programming.

As stated earlier the Simplex Method (or its variations e.g. Dual Simplex Method) has thus far been the most effective and widely used general method for the solution of linear programming problems. The Simplex Method in its various forms starts initially with a basic feasible solution and continues its moves in different iterations within the feasible region till it finds the optimal solution. The only other notable variation of the Simplex Method, namely the Dual Simplex Method, on the other hand, by virtue of the special formulation of the linear programming problem, starts with an in-feasible solution and continues to move in the in-feasible region till it finds the optimal solution at which it enters the feasible region. In other respects both the Simplex and the Dual Simplex Methods follow essentially the same principle for obtaining the optimal solution. The rigorous mathematical features have been widely discussed in the literature [12, 16, 34, 35, 38, 68, 77] and only those formal aspects of this topic which are closely related to the subject of this thesis will be outlined. The Multiplex Method, though reported in the literature [30, 15, 69, 71, 29, 32], is not so well known and has also not been widely coded on electronic computers. It had earlier been programmed for the English Electric's Computer ‘DEUCE' by the author [72] and Ferranti's ‘MERCURY' by Ole-John Dahl in 1960 [15]. Later both the above mentioned computers were obsolete and the efforts presently concentrate on coding it for UNIVAC 1100 and IBM 360. The Multiplex Method, as such, has been included in the present thesis and discussed in some detail in chapter 2. The flow diagram and the algorithm for the method is given in section 2.4, chapter 2. The main body of the thesis consists of developing a new linear programming method which has been called the Bounding Hyperplane Method – Part I. This is explained in detail in chapter 3. The method could initially start with either a basic feasible or in-feasible point and in its subsequent moves it may either alternate between the feasible and the in-feasible regions or get restricted to either of them depending upon the problem. It is applicable as a new phase which we call phase 0 to the Simple Method, particularly in situations where an initial basic feasible point is not available. In such cases it either results in a feasible point at the end of phase 0 or else yields a ‘better' in-feasible point for phase 1 operations of the Simplex Method. Moreover, it is found that the number of iterations required to reach either the former by the application of phase 0 or the latter by the application of first phase 0 and then phase 1 are, in general, less than those required by following phase 1 alone. This is explained with illustrations in Chapter 6. Even when applied alone the method, in general, yields the optimal solution in fewer iterations as compared with the Simplex Method. This is illustrated with examples in chapter 3. We also develop and illustrate a powerful but straight-forward method whereby we first find the solution to the equality constraints and (if the former does not yield an inconsistent solution point) then the transformations to the latter are obtained from the equality solution tableau corresponding to the former. This results in reducing the iteration time appreciably for each iteration of the method. It has been called the B.H.P.M. – part II and is discussed in chapter 4. To estimate the time taken by the B.H.P and the Simplex Method, the two codes (written in Fortran) have been run on a number of problems taken from the literature. The results have been summarised in chapter 7. Finally, the suggestions for further research towards i. the extensions of the B.H.P.M. to the quadratic programming problem where the function in (1.1.1) is positive semi-definite, and (ii) the accuracy of computations in linear programming, in general, are discussed in sections 8.1 and 8.2 respectively of chapter 8.

This thesis reports on research undertaken in an exploration of the use of formal semantics for student modelling in intelligent tutoring systems. The domain chosen was that of tutoring programming languages and within that domain Prolog was selected to be the target language for this exploration. The problem considered is one of how to analyse students' errors at a level which allows diagnosis to be more flexible and meaningful than is possible with the 'mal-rules' and 'bugcatalogue' approach of existing systems. The ideas put forward by Robin Milner [1980] in his Calculus of Communicating Systems (CCS) form the basis of the formalism which is proposed as a solution to this problem. Based on the findings of an empirical investigation, novices' misconceptions of control flow in Prolog was defined as a suitable area in which to explore the application of this solution. A selection of Prolog programs used in that investigation was formally described in terms of CCS. These formal descriptions were used by a production rule system to generate a number of the incomplete or faulty models of Prolog execution which were identified in the first empirical study. In a second empirical study, a machine-analysis tool, designed to be part of a diagnostic tutoring module, used these models to diagnose students' misconceptions of Prolog control flow. This initial application of CCS to student modelling showed that the models of Prolog execution generated by the system could be used successfully to detect students' misunderstandings. Results from the research reported here indicate that the use of formal semantics to model programming languages has a useful contribution to make to the task of student modelling.