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Specify LMI System at the Command Line  The following tutorial
example is used to illustrate the specification of LMI systems
with the LMI Lab tools.  Specifying LMI System  Consider a
stable transfer function   with four inputs, four outputs, and
six states, and consider the set of input/output scaling
matrices D with block-diagonal structure   The following problem
arises in the robust stability analysis of systems with time-
varying uncertainty [4]:  Find, if any, a scaling D of structure
(Equation 4-5) such that the largest gain across frequency of D
G(s) D–1 is less than one.  This problem has a simple LMI
formulation: there exists an adequate scaling D if the following
feasibility problem has solutions:  Find two symmetric matrices
XR6×6 and S = DT DR4×4 such that   The LMI system (Equation 4-6,
Equation 4-7, and Equation 4-8) can be described with the LMI
Editor as outlined below. Alternatively, its internal
description can be generated with