Closed-Form Expressions for the Noncompact Part of $Sp(2n)$

In a comment on the paper of Habib and Ryne, chao-dyn/9406010 and Phys.Rev.Lett. vol.74, 70 (1995), I point out that the Iwasawa decomposition of the symplectic group can be used to write down closed-form expressions for the noncompact part of the group and thus to compute the Lyapunov exponents in systems with more than two degrees of freedom using the cited method.