Seberry has contributed to the knowledge and use of Hadamard matrix|Hadamard
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For the case of two levels (L=2), Plackett and Burman used the method found in 1933 by Raymond Paley for generating orthogonal matrices whose elements are all either 1 or -1 (Hadamard matrices).
Regular Hadamard matrix, a Hadamard matrix whose row and column sums are all equal.