Proof of (2.40)

Dear Professor Skogestad

May I ask you a question on your new book "Multivariable
Feedback Control" ?
On page 34 you derive relationsships between gain margin and
the maximum of sensitiviy Ms or complementary sensitivity, Mt.
When I recalculate the proof for the left part of (2.40),
I always get GM >= 1 - 1/Mt but not the plus sign of (2.40).

It is very probable that I do something wrong in the derivation
of that result (although I get the same for (2.39)).
Since I haven't found this to be a misprint in your misprint
page (version 8/21/96), I thank you very much for a short
comment if (2.40) is correct (and I'm calculating wrong).

Thank you very much for your attention
Thomas Guettinger

P.S.: I am very found of your book - it's written so precise
      and easy to understand !

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| Thomas E. Guettinger Tf: ++41 1 632 37 04 |
| Dipl. Chem. Eng. ETH Fax: ++41 1 632 12 11 |
| Automatic Control Laboratory E-Mail (preferred): |
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Received on Wed Aug 28 08:52:08 1996