Document # Factoring Polynomials over Finite Fields with Linear Galois Groups: An Additive Combinatorics Approach

### Author Zeyu Guo  ## File

LIPIcs.MFCS.2020.42.pdf
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• 14 pages

## Acknowledgements

The author is grateful to Nitin Saxena for helpful discussions.

## Cite As

Zeyu Guo. Factoring Polynomials over Finite Fields with Linear Galois Groups: An Additive Combinatorics Approach. In 45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 170, pp. 42:1-42:14, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2020)
https://doi.org/10.4230/LIPIcs.MFCS.2020.42

## Abstract

Let f̃(X) ∈ ℤ[X] be a degree-n polynomial such that f(X): = f̃(X)od p factorizes into n distinct linear factors over 𝔽_p. We study the problem of deterministically factoring f(X) over 𝔽_p given f̃(X). Under the generalized Riemann hypothesis (GRH), we give an improved deterministic algorithm that computes the complete factorization of f(X) in the case that the Galois group of f̃(X) is (permutation isomorphic to) a linear group G ≤ GL(V) on the set S of roots of f̃(X), where V is a finite-dimensional vector space over a finite field 𝔽 and S is identified with a subset of V. In particular, when |S| = |V|^{Ω(1)}, the algorithm runs in time polynomial in n^{log n/(log log log log n)^{1/3}} and the size of the input, improving Evdokimov’s algorithm. Our result also applies to a general Galois group G when combined with a recent algorithm of the author. To prove our main result, we introduce a family of objects called linear m-schemes and reduce the problem of factoring f(X) to a combinatorial problem about these objects. We then apply techniques from additive combinatorics to obtain an improved bound. Our techniques may be of independent interest.

## Subject Classification

##### ACM Subject Classification
• Mathematics of computing → Computations in finite fields
• Mathematics of computing → Computations on polynomials
• Mathematics of computing → Combinatoric problems
• Computing methodologies → Algebraic algorithms
##### Keywords
• polynomial factoring
• permutation group
• finite field
• algebraic combinatorics
• derandomization

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## References

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