Word length perturbations in certain symmetric presentations of dihedral groups

Abstract

Given a finite group with a generating subset there is a well-established notion of length for a group element given in terms of its minimal length expression as a product of elements from the generating set. Recently, certain quantities called ${\lambda }_1$ and ${\lambda }_2$ have been defined that allow for a precise measure of how stable a group is under certain types of small perturbations in the generating expressions for the elements of the group. These quantities provide a means to measure differences among all possible paths in a Cayley graph for a group, establish a group theoretic analog for the notion of stability in nonlinear dynamical systems, and play an important role in the application of groups to computational genomics. In this paper, we further expose the fundamental properties of ${\lambda }_1$ and ${\lambda }_2$ by establishing their bounds when the underlying group is a dihedral group. An essential step in our approach is to completely characterize so-called symmetric presentations of the dihedral groups, providing insight into the manner in which ${\lambda }_1$ and ${\lambda }_2$ interact with finite group presentations. This is of interest independent of the study of the quantities ${\lambda }_1,{\lambda }_2$. Finally, we discuss several conjectures and open questions for future consideration.