Tridiagonal: [A] = [Q][D][Q]H Any square symmetric (hermitian) matrix [A] can be factorized by
similarity transformations into the form, [A]=[Q][D][Q]-1 where [Q] is an orthogonal (unitary)
matrix and [D] is a real symmetric tridiagonal matrix. Note that [D] can/should be made real even when [A]
has complex elements. Since [Q] is orthogonal (unitary) [Q]-1 = [Q]H and when it is
real [Q]H = [Q]T.