arXiv subjects

Sarah Rees

Publications and source records attributed to Sarah Rees.

39 records · Page 3Linked to original sources

arXiv1997

A language theoretic analysis of combings

A group is combable if it can be represented by a language of words satisfying a fellow traveller property; an automatic group has a synchronous combing which is a regular language. This paper gives a systematic analysis of the properties of groups with combings in various formal language classes, and of the closure properties of the associated classes of groups. It generalises previous work, in particular of Epstein et al. and Bridson and Gilman.

math.GR↗

arXiv1997

Automatic groups associated with word orders other than shortlex

The existing algorithm to compute and verify the automata associated with an automatic group deals only with the subclass of shortlex automatic groups. This paper describes the extension of the algorithm to deal with automatic groups associated with other word orders (the algorithm has now been implemented ) and reports on the use of the algorithm for specific examples; in particular a very natural automatic (or asynchonously automatic) structure for the Baumslag-Solitar and related classes of groups (closely related to one described for some of those groups by Epstein et al. is found from a wreath product order over shortlex.

math.GR↗

arXiv1994

Recognizing badly presented Z-modules

Finitely generated Z-modules have canonical decompositions. When such modules are given in a finitely presented form there is a classical algorithm for computing a canonical decomposition. This is the algorithm for computing the Smith normal form of an integer matrix. We discuss algorithms for Smith normal form computation, and present practical algorithms which give excellent performance for modules arising from badly presented abelian groups. We investigate such issues as congruential techniques, sparsity considerations, pivoting strategies for Gauss-Jordan elimination, lattice basis reduction and computational complexity. Our results, which are primarily empirical, show dramatically improved performance on previous methods.

math.GR↗