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Nonlinear Control Sy.. - Free

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314 APPENDIX A. PROOFS<br />

Since the equilibrium is globally asymptotically stable, there exist k1, k2 such that (see, for<br />

example, Chen [15] pp. 404)<br />

kle-k2(t-to)<br />

Ix(t)II <<br />

Thus<br />

xTPx = f<br />

t<br />

ft<br />

00<br />

1<br />

kle-k2(T-t) Q(T)kle-k2(T-t) dT<br />

k2Q(T)e-2k2(T-t) dr.<br />

The boundedness of Q(t) implies that there exist M: 11Q(t)II < M. Thus<br />

t "0<br />

or<br />

2<br />

xTPx < kM<br />

2<br />

Also, this implies that xTPx < A2IIx1I2 On the other hand, since Q is positive definite,<br />

3a > 0 such that xT Qx > axT x. Also, A bounded implies that I I A(t) I I < N, Vt E R. Thus<br />

Thus,<br />

or<br />

xTPx = J<br />

t<br />

1<br />

k2Me-2k2(T-t) dr.<br />

00<br />

xT4T (T, t)Q(T)d)(T, t)x dT<br />

x(T)TQ(T)x(T) d7<br />

f' aIIAN)II IIx(T)II2 dT<br />

f ' N II x(T)T A(T)x(T) II dT<br />

> II f Nx(T)T drx(T) dTII NxTx.<br />

xTPx > a NxTx<br />

AlIIxII2

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