the algorithms proposed in [1] and [2].

  If the given transfer-function matrix G is unstable, then a right
  coprime factorization with inner denominator of G is first
  computed
            -1
     G = Q*R  ,

  where Q and R are stable transfer-function matrices and R is
  inner. If G is stable, then Q = G and R = I.
  Let (AQ,BQ,CQ,DQ) be the state-space representation of Q.

  If DICO = 'C', then the L2-norm of G is computed as

     NORM2(G) = NORM2(Q) = SQRT(TRACE(BQ'*X*BQ)),

  where X satisfies th