en G:

  1) Decompose additively G as

       G = G1 + G2,

     such that G1 = (As,Bs,Cs,D) has only ALPHA-stable poles and
     G2 = (Au,Bu,Cu) has only ALPHA-unstable poles.

  2) Determine G1r, a reduced order approximation of the
     ALPHA-stable part G1 using the balancing stochastic method
     in conjunction with either the B&T [1,2] or SPA methods [3].

  3) Assemble the reduced model Gr as

        Gr = G1r + G2.

  Note: The employed stochastic truncation algorithm [2,3] has the
  property that 