Designs, Codes and Cryptography

, Volume 68, Issue 1–3, pp 179–194 | Cite as

On the classification of nonsingular 2×2×2×2 hypercubes

Article

Abstract

As a first step in the classification of nonsingular 2×2×2×2 hypercubes up to equivalence, we resolve the case where the base field is finite and the hypercubes can be written as a product of two 2×2×2 hypercubes. (Nonsingular hypercubes were introduced by D. Knuth in the context of semifields. Where semifields are related to hypercubes of dimension 3, this paper considers the next case, i.e., hypercubes of dimension 4.) We define the notion of ij-rank (with 1 ≤ i < j ≤ 4) and prove that a hypercube is the product of two 2×2×2 hypercubes if and only if its 12-rank is at most 2. We derive a ‘standard form’ for nonsingular 2×2×2×2 hypercubes of 12-rank less than 4 as a first step in the classification of such hypercubes up to equivalence. Our main result states that the equivalence class of a nonsingular 2×2×2×2 hypercube M of 12-rank 2 depends only on the value of an invariant δ0(M) which derives in a natural way from the Cayley hyperdeterminant det0M and another polynomial invariant det M of degree 4. As a corollary we prove that the number of equivalence classes is (q + 1)/2 or q/2 depending on whether the order q of the field is odd or even.

Keywords

Nonsingular hypercube Invariant Hyperdeterminant Classification Semifield 

Mathematics Subject Classification (2010)

20G40 15A72 12K10 

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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  1. 1.Department of Applied Mathematics and Computer ScienceGhent UniversityGentBelgium

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