arXiv subjects
Publications and source records attributed to Hassan Sedaghat.
We obtain a complete characterization of all orbits of a quadratic Collatz-type recursion called the divide-or-choose-2 rule. Each orbit either ends in a cycle whose period depends on the initial value or it goes to infinity. We specify which initial values generate periodic orbits, and also show that all other initial values generate orbits that go to infinity.
We show that polynomial recursions $x_{n+1}=x_{n}^{m}-k$ where $k,m$ are integers and $m$ is positive have no nontrivial periodic integral orbits for $m\geq3$. If $m=2$ then the recursion has integral two-cycles for infinitely many values of $k$ but no higher period orbits. We also show that these statements are true for all quadratic recursions.
A higher order difference equation may be generally defined in an arbitrary nonempty set S as: \[ f_{n}(x_{n},x_{n-1},...,x_{n-k})=g_{n}(x_{n},x_{n-1},...,x_{n-k}) \] where $f_{n},g_{n} :S^{k+1}\rightarrow S$ are given functions for $n=1,2,... $ and $k$ is a positive integer. We present conditions that imply the above equation can be factored into an equivalent pair of lower order difference equations using possible form symmetries (order-reducing changes of variables). These results extend and generalize semiconjugate factorizations of recursive difference equations on groups. We apply some of this theory to obtain new factorization results for the important class of quadratic difference equations on algebraic fields. We also discuss the nontrivial issue of the existence of solutions for quadratic equations.
The existence of a semiconjugate relation permits the transformation of a higher order difference equation on a group into an equivalent triangular system of two difference equations of lower orders. Introducing time-dependent form symmetries in this paper enables us to identify the semiconjugate property in a larger set of non-autonomous difference equations than previously considered. We show that there is a substantial class of equations having this feature that includes the general (non-autonomous, non-homogeneous) linear equation with variable coefficients in an arbitrary algebraic field.