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LMIs in Control/pages/Small Gain Theorem

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LMIs in Control/Matrix and LMI Properties and Tools/Small Gain Theorem

The Small Gain Theorem provides a sufficient condition for the stability of a feedback connection.


Theorem

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Suppose is a Banach Algebra and . If , then exists, and furthermore,

                    

Proof

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Assuming we have an interconnected system :

and,


The above equations can be represented in matrix form as


Making the subject, we then have:


If is well-behaved, then the interconnection is stable. For to be well-behaved, must be finite.

Hence, we have

and for the higher exponents of to converge to


Conclusion

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If , then this implies stability, since the higher exponents of in the summation of will converge to , instead of blowing up to infinity.


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A list of references documenting and validating the LMI.


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