ABSTRACT
In 1893, Hadamard [59] addressed the problem of the maximum absolute value of the determinant of an n×n complex matrix H with all its entries on a unit circle. The maximum value is
√ nn. Among real matrices, this value is
attained if and only if H has every entry either 1 or −1, and satisfies HHT = nI. (14.1)
Such matrices had appeared earlier [149], in the case where H is a power of 2, but they are now called Hadamard matrices.
