** Hessenberg form. **

** The Hessenberg form of a matrix is zero below the first **

** subdiagonal. If the matrix is symmetric or Hermitian, **

** the form is tridiagonal. [P,H] = HESS(A) produces a unitary **

** matrix P and a Hessenberg matrix H so that A = P*H*P' and **

** P'*P = EYE (P). By itself, HESS(A) returns H. **

** **