Hadamard matrix
An Hadamard matrix of size "m" is an "m" × "m" matrix H whose entries are ±1 such that HH⊤  = mIm, where H⊤ is the transpose of H and I"m" is the "m" × "m" identity matrix. An Hadamard matrix can be put into "standardized form" (that is, converted to an equivalent Hadamard matrix) where the first row and first column entries are all +1. If the size "m" &gt; 2 then "m" must be a multiple of 4.