  Let (A,b,c,d) be a SISO system. Its transfer function is computed
  as follows:

  1) Find a controllable realization (Ac,bc,cc) of (A,b,c).
  2) Find an observable realization (Ao,bo,co) of (Ac,bc,cc).
  3) Compute the r eigenvalues of Ao (the poles of (Ao,bo,co)).
  4) Compute the zeros of (Ao,bo,co,d).
  5) Compute the gain of (Ao,bo,co,d).

  This algorithm can be implemented using only orthogonal
  transformations [1]. However, for better efficiency, the
  implementation in TB04CD uses one elementary