Rédei permutations with the same cycle structure

Let Fq be the finite field of order q, and P1(Fq)=Fq∪{∞}. Write (x+y)m as N(x,y)+D(x,y)y. For m∈N and a∈Fq, the Rédei function Rm,a:P1(Fq)→P1(Fq) is defined by N(x,a)/D(x,a) if D(x,a)≠0 and x≠∞, and ∞, otherwise. In this paper we give a complete characterization of all pairs (m,n)∈N2 such that the R...

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Bibliographic Details
Published in:Finite fields and their applications Vol. 81; p. 102046
Main Authors: Capaverde, Juliane, Masuda, Ariane M., Rodrigues, Virgínia M.
Format: Journal Article
Language:English
Published: Elsevier Inc 01-08-2022
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Summary:Let Fq be the finite field of order q, and P1(Fq)=Fq∪{∞}. Write (x+y)m as N(x,y)+D(x,y)y. For m∈N and a∈Fq, the Rédei function Rm,a:P1(Fq)→P1(Fq) is defined by N(x,a)/D(x,a) if D(x,a)≠0 and x≠∞, and ∞, otherwise. In this paper we give a complete characterization of all pairs (m,n)∈N2 such that the Rédei permutations Rm,a and Rn,b have the same cycle structure when a and b have the same quadratic character and q is odd. We explore some relationships between such pairs (m,n), and provide explicit families of Rédei permutations with the same cycle structure. When a Rédei permutation has a unique cycle structure that is not shared by any other Rédei permutation, we call it isolated. We show that the only isolated Rédei permutations are the isolated Rédei involutions. Moreover, all our results can be transferred to bijections of the form mx and xm on certain domains.
ISSN:1071-5797
1090-2465
DOI:10.1016/j.ffa.2022.102046