 compute a symplectic QR decomposition of a real 2M-by-N matrix
  [A; B],

            [ A ]             [ R11  R12 ]
            [   ] = Q * R = Q [          ],
            [ B ]             [ R21  R22 ]

  where Q is a symplectic orthogonal matrix, R11 is upper triangular
  and R21 is strictly upper triangular.
  If [A; B] is symplectic then, theoretically, R21 = 0 and
  R22 = inv(R11)^T. Unblocked version.

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<A name="Specification"><B><FONT SIZE="+1">Specification</FONT></B></A>
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