Instytut Matematyczny Polskiej Akademii Nauk / Institute of Mathematics / Publishing house / Journals and Serials / Acta Arithmetica / All issues

Abstract

Two rational functions $f,g\in \mathbb F_q(X)$ are said to be equivalent if there exist $\phi ,\psi \in \mathbb F_q(X)$ of degree $1$ such that $g=\phi \circ f\circ \psi $. We give an explicit formula for the number of equivalence classes of rational functions of a given degree in $\mathbb F_q(X)$. This result should provide guidance for the current and future work on classifications of low degree rational functions over finite fields. We also determine the number of equivalence classes of polynomials of a given degree in $\mathbb F_q[X]$.