Theodore S. Norvell

Aggregative closure: an extension of transitive closure

The aggregative closure operator is defined and its usefulness is demonstrated in a wide variety of applications. The concepts and definitions of closed semirings and the aggregating relational operators provide a mathematical framework for the presentation of algorithms for these applications. A novel algorithm is also presented which is intended for the computation of the aggregate closure. All of these algorithms but the last are generalizations of existing algorithms intended for transitive closure.<<ETX>>

Machine Code Programs are Predicates Too

I present an interpretation of machine language programs as boolean expressions. Source language programs may also be so interpreted. The correctness of a code generator can then be expressed as a simple relationship between boolean expressions. Code generators can then be calculated from their specification.

Developing mental models of computer programming interactively via the web

A website featuring interactive examples used to teach introductory programming to both on-campus and, recently, distance students is described. On-line notes are created using a pair of tools, Web-Writer++, an authoring system for programming instructors, and the Teaching Machine, a program animator which is used to interactively display the examples. The tools allow the instructor in the classroom or the student on their own to step through computer programs written in C++ or Java. The animations that unfold are designed to build a deep understanding of how computers process programs, consonant with the kind of mental models we believe professional programmers hold. In-class versus distance experience will be discussed.

Logical Specifications for Functional Programs

We present a formal method of functional program development based on step-by-step transformation.

Program and Algorithm Visualization in Engineering and Physics

We report here on our experiences using a program animation tool, the Teaching Machine, for program and algorithm visualization for engineering and physics students at two universities: Memorial University, where it has been used since 1999 for teaching engineering students, and the University of Athens, where it was adopted in 2005 to teach physics students.

Integrating test generation functionality into the Teaching Machine environment

We propose an extension of the Teaching Machine project, called Quiz Generator, that allows instructors to produce assessment quizzes in the field of algorithm and data structures quite easily. This extension makes use of visualization techniques and is based on new features of the Teaching Machine that allow third-party visualizers to be added as plugins and for new scripting capabilities. Using these new capabilities, several quiz types have already been produced, which can be applied to any algorithm and/or data structure for which the necessary visualizer plugins exist.

Interactive embedded examples: a demonstration

A demonstration of the integration of a program animation tool into a set of web based notes used by instructors for lecturing and students for studying. Standard, conventionally prepared C++ and Java examples are dynamically incorporated into the class notes and can be interactively run in the animation tool directly from within the notes.

Compiling parallel applications to Coarse-Grained Reconfigurable Architectures

In this paper a novel approach for compiling parallel applications to a target coarse-grained reconfigurable architecture (CGRA) is presented. We have given a formal definition of the compilation problem for the CGRA. The application will be written in HARPO/L, a parallel object oriented language suitable for hardware. HARPO/L is first compiled to a data flow graph (DFG) representation. The remaining compilation steps are a combination of three tasks: scheduling, placement and routing. For compiling cyclic portions of the application, we have adapted a modulo scheduling algorithm: modulo scheduling with integrated register spilling. For scheduling, the nodes of the DFG are ordered using the hypernode reduction modulo scheduling (HRMS) method. The placement and routing is done using the neighborhood relations of the PEs.

Predicative semantics of loops

A predicative semantics is a mapping of programs to predicates. These predicates characterize sets of acceptable observations. The presence of time in the observations makes the obvious weakest fixed-point semantics of iterative constructs unacceptable. This paper proposes an alternative. We will see that this alternative semantics is monotone and implementable (feasible). Finally a programming theorem for iterative constructs is proposed, proved, and demonstrated. A novel aspect of this theorem is that it is not based on invariants.

Mapping loops onto Coarse-Grained Reconfigurable Architectures using Particle Swarm Optimization

Coarse-Grained Reconfigurable Architectures (CGRAs) have gained currency in recent years due to their abundant parallelism and flexibility. To utilize the abundant parallelism found in CGRAs, we propose a fast and efficient Modulo-Constrained Hybrid Particle Swarm Optimization (MCHPSO) scheduling algorithm to exploit loop level parallelism in applications. PSO has been proved to be successful in many applications in continuous optimization problems. In this paper, we show that PSO is capable of software pipelining loops by overlapping placement, scheduling and routing of successive loop iterations and executing them in parallel. Our proposed algorithm has been experimentally validated on various DSP benchmarks under two different architecture configurations. These experiments indicate that the proposed MCHPSO algorithm can find schedules with small initiation intervals within a reasonable amount of time. PSO is thus a promising alternative for obtaining near optimal solutions to this NP-hard scheduling problem.