Algorithms for Nielsen type periodic numbers of maps with remnant on surfaces with boundary and on bouquets of circles I

Abstract

In this paper and its sequel we present a method that, under loose restric- tions, is algorithmic for calculating the Nielsen type numbers N n(f) and NPn(f) of self maps f of hyperbolic surfaces with boundary and also of bouquets of circles. Because self maps of these surfaces have the same homotopy type as maps on wedges of circles, and the Nielsen periodic numbers are homotopy type invariant, we need concentrate only on the latter spaces. Of course the results will then automatically apply to the former spaces as well. The algorithm requires only that f has minimal remnant, by which we mean that there is limited cancellation between thef images of generators of the fundamental group. These methods often work even when the minimal remnant condition is not satised. Our methodology involves three separate techniques. Firstly, beginning with an endo- morphism h on the fundamental group, we adapt an algorithm of Wagner to our setting, allowing us to distinguish non-empty Reidemeister classes for iterates of a special represen- tative map for h, which we introduce. Secondly, using techniques reminiscent of symbolic dynamics, we assign key algebraic information to the actual periodic points of this special representative. Finally, we use word length arguments to prove that the remaining infor- mation required for the calculation of N n(f) and NPn(f) can be found with a nite computer search. We include many illustrative examples. In this rst paper we give the tools we need in order to present and give the algorithm for NPn(f). All the tools introduced here will be needed in the sequel where we develop the extra tools needed in order to compute N n(f).