Classification of Hadamard matrices of order 28 with hall sets

AbstractWe constructed 480 inequivalent Hadamard matrices with Hall sets of order 28 in Kimura (1988) and Kimura and Ohmori (1987). These matrices were classified by K-matrices and K-boxes associated with Hadamard matrices. In this paper we introduce some order on subsets of equivalence classes. By choosing maximal or minimal elements of these subsets, we get a complete classification and obtain 486 inequivalent matrices of order 28 with Hall sets