Comments, with reply, on 'Cumulants: a powerful tool in signal processing' by G.B. Giannakis

A counterexample is presented to show that the solution to the stochastic realization problem given in the above-titled letter (ibid., vol.75, no.9, p.1333-4, Sept. 1987) does not apply, in general, to the infinite impulse response systems. The author expands on the comments.<
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