Table of Contents
International Journal of Computational Mathematics
Volume 2014 (2014), Article ID 321585, 16 pages
Research Article

On the Dynamics of Laguerre’s Iteration Method for Finding the th Roots of Unity

1Mathematics Department, Augsburg College, 2211 Riverside Avenue, Minneapolis, MN 55454, USA
2Augsburg College, 2211 Riverside Avenue, Minneapolis, MN 55454, USA

Received 8 May 2014; Accepted 21 August 2014; Published 26 November 2014

Academic Editor: Yaohang Li

Copyright © 2014 Pavel Bělík et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Previous analyses of Laguerre’s iteration method have provided results on the behavior of this popular method when applied to the polynomials , . In this paper, we summarize known analytical results and provide new results. In particular, we study symmetry properties of the Laguerre iteration function and clarify the dynamics of the method. We show analytically and demonstrate computationally that for each the basin of attraction to the roots is a subset of an annulus that contains the unit circle and whose Lebesgue measure shrinks to zero as . We obtain a good estimate of the size of the bounding annulus. We show that the boundary of the basin of convergence exhibits fractal nature and quasi self-similarity. We also discuss the connectedness of the basin for large values of . We also numerically find some short finite cycles on the boundary of the basin of convergence for . Finally, we demonstrate that when using the floating point arithmetic and the general formulation of the method, convergence occurs even from starting values outside of the basin of convergence due to the loss of significance during the evaluation of the iteration function.