On equivalence of Hadamard matrices
In this important, careful, paper the author shows there are over 476 inequivalent Hadamard matrices of order 28. He defines and uses K- matrices, which have entries defined by the inner products of four rows at a time (analogous to a 4-profile) of an Hadamard matrix, to obtain this result. He then exhibits further Hadamard matrices which have the same K-matrix but differ using six rows (analogous to a 6-profile). Inequivalent Hadamard matrices of order 28 have also been studied by V. D. Tonchev.
scientific article; zbMATH DE number 4135958