re
  triangularized by applying unitary transformations Q2 and Z2 to
  Q1'*(sE-A)*Z1.

  If MODE = 'S', then the pencil sE(eps,inf)-A(eps,inf) in (1) is
  separated into sE(eps)-A(eps) and sE(inf)-A(inf) by applying
  unitary transformations Q3 and Z3 to Q2'*Q1'*(sE-A)*Z1*Z2.

  This gives

             | sE(eps)-A(eps) |        X       |      X     |
             |----------------|----------------|------------|
             |        O       | sE(inf)-A(inf) |      X     |
  Q'(sE-A)Z =|====================