If X is a symmetric Hadamard matrix, Y is a skew-Hadamard matrix, and XYT is symmetric, then X and Y are said to be amicable Hadamard matrices. A construction for amicable Hadamard matrices is given, and then amicable Hadamard matrices are used to generalize a construction for skew-Hadamard matrices.
History
Citation
Jennifer Seberry Wallis, Amicable Hadamard matrices, Journal of Combinatorial Theory, Ser. A., 11, (1971), 296-298.