Periods of orbits for maps on graphs homotopic to a constant map

Chris Bernhardt, Zach Gaslowitz, Adriana Johnson, Whitney Radil

Published 2011-08-14, updated 2012-04-25Version 3

The paper proves two theorems concerning the set of periods of periodic orbits for maps of graphs that are homotopic to the constant map and such that the vertices form a periodic orbit. The first result is that if $v$ is not a divisor of $2^k$ then there must be a periodic point with period $2^k$. The second is that if $v=2^ks$ for odd $s>1$, then for all $r>s$ there exists a periodic point of minimum period $2^k r$. These results are then compared to the Sharkovsky ordering of the positive integers. (The final version of this paper will appear in the Journal of Difference Equations and Applications.)