Jacket matrix order 4 and Mersenne matrix order 3
Jacket matrix  is a square matrix A of order n, defined by inversed matrix B=A–1 which entries are proportional to inversed entries of transposed matrix: nBij=1/ATij, AB=BA=I. Jacket matrices includes Hadamard matrices.
1. Ken Fenlayson, Moon Ho Lee, Jennifer Seberry, and Meiko Yamada, Jacket Matrices constructed from Hadamard matrices and generalized Hadamard matrices. Australian Journal of Combinatorics, Vol. 35, 2006, pp. 83–87. WIKI  |  |