Noncommutativity in the analysis of piecewise discrete-time dynamical systems

Abstract

In this paper, we present a new method for the analysis of piecewise dynamical systems that are similar to the Collatz conjecture in regard to certain properties of the commutator of their sub-functions. We use the fact that the commutator of polynomials $E(n)=n/2$ and $O(n)=(3n+1)/2$ is constant to study rearrangements of compositions of $E(n)$ and $O(n)$. Our main result is that for any positive rational number $n$, if $(E^{e_1} \circ O^{o_1} \circ E^{e_2} \circ \dotsb \circ O^{o_l} \circ E^{e_{l+1}})(n)=1$, then $(E^{e_1} \circ O^{o_1} \circ E^{e_2} \circ \dotsb \circ O^{o_l} \circ E^{e_{l+1}})(n) = \lceil(E^{e_1 + \dotsb + e_{l+1}} \circ O^{o_1 + \dotsb + o_{l}})(n)\rceil$, where exponentiation is used to denote repeated composition and $e_i$ and $o_i$ are positive integers. Composition sequences of this form have significance in the context of the Collatz conjecture. The techniques used to derive this result can be used to produce similar results for a wide variety of repeatedly composed piecewise functions.