Showing papers by "Richard Cole published in 2001"

Optimised Predecessor Data Structures for Internal Memory

Abstract: We demonstrate the importance of reducing misses in the translation-lookaside buffer (TLB) for obtaining good performance on modern computer architectures. We focus on data structures for the dynamic predecessor problem: to maintain a set S of keys from a totally ordered universe under insertions, deletions and predecessor queries. We give two general techniques for simultaneously reducing cache and TLB misses: simulating 3-level hierarchical memory algorithms and cache-oblivious algorithms. We give preliminary experimental results which demonstrate that data structures based on these ideas outperform data structures which are based on minimising cache misses alone, namely B-tree variants.

A faster implementation of the Goemans-Williamson clustering algorithm

Abstract: We give an implementation of the Goemans-Williamson clustering procedure which is at the core of several approximation algorithms including those for Generalized Steiner Trees, Prize Collecting Travelling Salesman, 2-Edge Connected Subgraph etc. On a graph with n nodes and m edge, our implementation gives O (k(n + m) log2n) time approximation algorithms for all these problems at the expense of a slight additive degradation of 1/nk in the approximation factor, for any constant k.

Overlap matching

Abstract: We propose a new paradigm for string matching, namely structural matching. In structural matching, the text and pattern contents are not important. Rather, some areas in the text and patterns are singled out, say intervals. A “match” is a text location where a specified relation between the text and pattern areas is satisfied.In particular we define the structural matching problem of Overlap (Parity) Matching. We seek the text locations where all overlaps of the given pattern and text intervals have even length. We show that this problem can be solved in time O(n log m), where the text length is n and the pattern length is m.As an application of overlap matching, we show how to reduce the String Matching with Swaps problem to the overlap matching problem. The String Matching with Swaps problem is the problem of string matching in the presence of local swaps. The best known deterministic upper bound for this problem was O(nm1/3 log m log s) for a general alphabet ∑, where s = min(m, ¦∑¦).Our reduction provides a solution to the pattern matching with swaps problem in time O(n log m log s).