       array must contain the (N+1)-th to (N+M)-th blocks in the
          first block row / column of an s.p.d. block Toeplitz
          matrix.
          On exit, if INFO = 0, the leading K-by-M*K / M*K-by-K part
          of this array contains information on the Householder
          transformations used, such that the array

                     [ T  TA ]    /    [ T  ]
                                       [ TA ]

          serves as the new transformation matrix T for further
          applications 