Efficient Parallel Algorithms for Closest Point Problems

TL;DR: This dissertation develops and studies fast algorithms for solving closest point problems, and introduces new parallel algorithms for these problems that are both efficient and practical, and presents a simple and flexible programming model for designing and analyzing parallel algorithms.

Abstract: This dissertation develops and studies fast algorithms for solving closest point problems. Algorithms for such problems have applications in many areas including statistical classification, crystallography, data compression, and finite element analysis. In addition to a comprehensive empirical study of known sequential methods, I introduce new parallel algorithms for these problems that are both efficient and practical. I present a simple and flexible programming model for designing and analyzing parallel algorithms. Also, I describe fast parallel algorithms for nearest-neighbor searching and constructing Voronoi diagrams. Finally, I demonstrate that my algorithms actually obtain good performance on a wide variety of machine architectures. The key algorithmic ideas that I examine are exploiting spatial locality, and random sampling. Spatial decomposition provides allows many concurrent threads to work independently of one another in local areas of a shared data structure. Random sampling provides a simple way to adaptively decompose irregular problems, and to balance workload among many threads. Used together, these techniques result in effective algorithms for a wide range of geometric problems. The key experimental ideas used in my thesis are simulation and animation. I use algorithm animation to validate algorithms and gain intuition about their behavior. I model the expected performance of algorithms using simulation experiments, and some knowledge as to how much critical primitiive operations will cost on a given machine. In addition, I do this without the burden of esoteric computational models that attempt to cover every possible variable in the design of a computer system. An iterative process of design, validation, and simulation delays the actual implementation until as many details as possible are accounted for. Then, further experiments are used to tune implementations for better performance.