Lyapunov Transformation

A non-degenerate linear transformation $ L ( t) : \mathbf R ^ {n} \rightarrow \mathbf R ^ {n} $( or $ L ( t) : \mathbf C ^ {n} \rightarrow \mathbf C ^ {n} $), smoothly depending on a parameter $ t \in \mathbf R $, that satisfies the condition

$$ \sup _ {t \in \mathbf R } [ \| L ( t) \| + \| L ^ {-1} ( t) \| + \| \dot{L} ( t) \| ] < + \infty . $$

It was introduced by A.M. Lyapunov in 1892 (see [1]). The Lyapunov transformation is widely used in the theory of linear systems of ordinary differential equations. In many cases the requirement

$$ \sup _ {t \in \mathbf R } \| \dot{L} ( t) \| < + \infty $$

can be discarded.

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