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A Remark on a Theorem of Lyapunov

Published online by Cambridge University Press:  20 November 2018

James S. W. Wong*
Affiliation:
Carnegie-Mellon University, Pittsburgh, Pennsylvania
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Consider the linear ordinary differential equation

1

where xEn, the n-dimensional Euclidean space and A is an n × n constant matrix. Using a matrix result of Sylvester and a stability result of Perron, Lyapunov [4] established the following theorem which is basic in the stability theory of ordinary differential equations:

Theorem (Lyapunov). The following three statements are equivalent:

(I) The spectrum σ(A) of A lies in the negative half plane.

(II) Equation (1) is exponentially stable, i.e. there exist μ, K>0 such that every solution x(t) of (1) satisfies

2

where ∥ ∥ denotes the Euclidean norm.

(III) There exists a positive definite symmetric matrix Q, i.e. Q=Q* and there exist q1,q2>0 such that

3

satisfying

4

where I is the identity matrix.

Type
Research Article
Copyright
Copyright © Canadian Mathematical Society 1970

References

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6. Stone, M. H., Linear transformations in Hilbert space and their applications to analysis, Amer. Math. Soc. Coll. XV, New York, (1932).Google Scholar