** HADAMARD(N) is a Hadamard matrix of order N, that is, **

** a matrix H with elements 1 or -1 such that H'*H = N* EYE (N). **

** An N-by-N Hadamard matrix with N > 2 exists only if REM (N,4)=0. **

** This function handles only the cases where N, N/12 or N/20 **

** is a power of 2. **

** **