e right, minimum
  phase spectral factor satisfying

      G1*conj(G1) = conj(W)* W,                      (3)

  G1 is the NS-order ALPHA-stable part of G, and INFNORM(G) is the
  infinity-norm of G. HSV(1), ... , HSV(NS) are the Hankel-singular
  values of the stable part of the phase system (Ap,Bp,Cp)
  with the transfer-function matrix

       P = inv(conj(W))*G1.

  If BETA &gt; 0, then the model reduction is performed on [G BETA*I]
  instead of G. This is the recommended approach to be used when D
  ha