Error in coprime factorization?

Dear Professor Sigurd Skogestad,
My name is Kazuya Sato. I'm one of the researcher at Saga University.
My current research area is robust control and descriptor system. Nowadays,
I proposed the Robust stabilization of descriptor system using normalized
left coprime factor description. I'll present this paper in Symposium in
Japan.

By the way, I bought your book 'Multivariable Feedback Control, Analysis
and Design.' I think it is very nice book because it is written good
explanation and there are a lot of examples which can implement by MATLAB.
But I found a few error. In Chapter 4, pp.118, it is described that the
normalized left coprime factrization. In this part, there is a equation

(A-BS^(-1)D^(T)C)Z+Z(A-BS^(-1)D^(T)C)^(T)-ZC^(T)R^(-1)CZ+BS^(-1)B^(T)=0.

I think this equation would be

(A-BD^(T)R^(-1)C)Z+Z(A-BD^(T)R^(-1)C)^(T)-ZC^(T)R^(-1)CZ+BS^(-1)B^(T)=0.

In your book, you may be reffered to the book which was written by
McFarlane and Glover. This book has same error as your book. But in
Appendix A of their book, that equation was described as my pointed one.
When I derived the normalized left coprime factrization actually, the
riccati equation would be my one.
So, In Chapter 9, pp378, the equation (9.67) should be revised.

I guess that my attention is correct. But if it is my misunderstand, please
let me know and forgive me.

Yours sincerely,
Kazuya Sato

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Kazuya Sato :
Production Division, Dept. of Mechanical Eng.
Faculty of Science and Engineering
Saga University
e-mail : sato@me.saga-u.ac.jp
URL : http://www.me.saga-u.ac.jp/~sato
Received on Wed Sep 11 04:56:08 1996