right half plane zeros of G1 remain as right half
  plane zeros of G1r. Thus, the order can not be chosen smaller than
  the sum of the number of unstable poles of G and the number of
  unstable zeros of G1.

  The reduction of the ALPHA-stable part G1 is done as follows.

  If JOB = 'B', the square-root stochastic Balance & Truncate
  method of [1] is used.
  For an ALPHA-stable continuous-time system (DICO = 'C'),
  the resulting reduced model is stochastically balanced.

  If JOB = 'F', the balancing-fre