2 triangular
  matrices corresponding to 2-by-2 diagonal blocks in A(:,:,H)
  are so reduced that their product is a 2-by-2 diagonal matrix.

  If COMPQ = 'U' or COMPQ = 'I', then the orthogonal factors are
  computed and stored in the array Q so that for S(I) = 1,

                      T
          Q(:,:,I)(in)   A(:,:,I)(in)   Q(:,:,MOD(I,K)+1)(in)
                                                              T  (1)
      =   Q(:,:,I)(out)  A(:,:,I)(out)  Q(:,:,MOD(I,K)+1)(out),

  and for S(I) = -1,

   