(Pseudo)-cocyclic (structured) Hadamard matrices over (quasi)groups

Abstract

Progressing on a survey of the state of the art of cocyclic constructions for Hadamard matrices, we will prove that the family of Goethals-Seidel Hadamard matrices is (pseudo)-cocyclic over a certain family of quasigroups. Therefore, what we call (pseudo)-cocyclic (structured) Hadamard matrices over (quasi)groups, precisely those matrices satisfying some kind of cocycle Hadamard test known so far, include most of the well-known and prolific constructions of Hadamard matrices. We will discuss also different approaches in order to look for large matrices of this type.