  The dual Youla method for closed loop identification is known to have several
practically important merits. Namely, it provides an accurate plant model
irrespective of noise models, and fits inherently to handle unstable plants by
using coprime factorization. In addition, the method is empirically robust
against the uncertainty of the controller knowledge. However, use of coprime
factorization may cause a big barrier against industrial applications. This
paper shows how to derive a simplified version of the method which identifies
the plant itself without coprime factorization, while enjoying all the merits
of the dual Youla method. This simplified version turns out to be identical to
the stabilized prediction error method which was proposed by the authors
recently. Detailed simulation results are given to demonstrate the above
merits.
