The functional graph of $f(X)=(cX^q+aX)(X^{q}-X)^{n-1}$ over quadratic extensions of finite fields

Abstract: Let $\mathbb{F}q$ be the finite field with $q=p^s$ elements, where $p$ is an odd prime and $s$ a positive integer. In this paper, we define the function $f(X)=(cX^q+aX)(X^{q}-X)^{n-1}$, for $a,c\in\mathbb{F}_q$ and $n\geq 1$. We study the dynamics of the function $f(X)$ over the finite field $\mathbb{F}{q^2}$, determining cycle lengths and number of cycles. We also show that all trees attached to cyclic elements are isomorphic, with the exception of the tree hanging from zero. We also present the general shape of such hanging trees, which concludes the complete description of the functional graph of $f(X)$.