## Foreword

Published in Mathematics in Computer Science

Published in Mathematics in Computer Science

Published in Mathematics in Computer Science

We give a new construction of the outer automorphism of the symmetric group on six points. Our construction features a complex Hadamard matrix of order six containing third roots of unity and the algebra of split quaternions over the real numbers.

Published in Mathematics in Computer Science

Covering arrays have been widely used to detect the presence of faults in large software and hardware systems. Indeed, finding failures that result from faulty interactions requires that all interactions that may cause faults be covered by a test case. However, finding the actual faults requires more, because the failures resulting from two potenti...

Published in Mathematics in Computer Science

Suppose there exists a Hadamard 2-(m,m-12,m-34)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(m,\frac{m-1}{2},\frac{m-3}{4})$$\end{document} design with skew incidenc...

Published in Mathematics in Computer Science

Let G=Cn1×⋯×Cnm\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$G=\mathbf{C}_{n_1}\times \cdots \times \mathbf{C}_{n_m}$$\end{document} be an abelian group of order n=n1...

Published in Mathematics in Computer Science

A way of generating cocyclic Hadamard matrices is described, which combines a new heuristic, coming from a novel notion of fitness, and a peculiar local search, defined as a constraint satisfaction problem. Calculations support the idea that finding a cocyclic Hadamard matrix of order 4·47\documentclass[12pt]{minimal} \usepackage{amsmath} \usepacka...

Published in Mathematics in Computer Science

A complex Hadamard matrix is defined as a matrix H which fulfills two conditions, |Hj,k|=1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$|H_{j,k}|=1$$\end{document} fo...

Published in Mathematics in Computer Science

In this paper, we give a characterization of quasi-Hadamard groups in terms of propelinear codes. We define a new class of codes that we call quasi-Hadamard full propelinear codes. Some structural properties of these codes are studied and examples are provided.

Published in Mathematics in Computer Science

We single out a class of difference families which is widely used in some constructions of Hadamard matrices and which we call Goethals–Seidel (GS) difference families. They consist of four subsets (base blocks) of a finite abelian group of order v, which can be used to construct Hadamard matrices via the well-known Goethals–Seidel array. We consid...

Published in Mathematics in Computer Science

We study a special class of (real or complex) robust Hadamard matrices, distinguished by the property that their projection onto a 2-dimensional subspace forms a Hadamard matrix. It is shown that such a matrix of order n exists, if there exists a skew Hadamard matrix or a symmetric conference matrix of this size. This is the case for any even n≤20\...