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PERMUTATION POLYNOMIALS OF DEGREE 8 OVER FINITE FIELDS OF ODD CHARACTERISTIC
- Part of
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- Journal:
- Bulletin of the Australian Mathematical Society / Volume 101 / Issue 1 / February 2020
- Published online by Cambridge University Press:
- 09 July 2019, pp. 40-55
- Print publication:
- February 2020
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- Article
- Export citation
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We give an algorithmic generalisation of Dickson’s method of classifying permutation polynomials (PPs) of a given degree
$d$ over finite fields. Dickson’s idea is to formulate from Hermite’s criterion several polynomial equations satisfied by the coefficients of an arbitrary PP of degree 
$d$. Previous classifications of PPs of degree at most 6 were essentially deduced from manual analysis of these polynomial equations, but this approach is no longer viable for 
$d>6$. Our idea is to calculate some radicals of ideals generated by the polynomials, implemented by a computer algebra system. Our algorithms running in SageMath 8.6 on a personal computer work very fast to determine all PPs of degree 8 over an arbitrary finite field of odd order 
$q>8$. Such PPs exist if and only if 
$q\in \{11,13,19,23,27,29,31\}$ and are explicitly listed in normalised form.
