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A singular version of Leighton's comparison theorem for forced quasilinear second order differential equations

Ondřej Došlý, Jaroslav Jaroš (2003)

Archivum Mathematicum

We extend the classical Leighton comparison theorem to a class of quasilinear forced second order differential equations ( r ( t ) | x ' | α - 2 x ' ) ' + c ( t ) | x | β - 2 x = f ( t ) , 1 < α β , t I = ( a , b ) , ( * ) where the endpoints a , b of the interval I are allowed to be singular. Some applications of this statement in the oscillation theory of (*) are suggested.

A smooth Lyapunov function from a class- 𝒦ℒ estimate involving two positive semidefinite functions

Andrew R. Teel, Laurent Praly (2010)

ESAIM: Control, Optimisation and Calculus of Variations

We consider differential inclusions where a positive semidefinite function of the solutions satisfies a class- 𝒦ℒ estimate in terms of time and a second positive semidefinite function of the initial condition. We show that a smooth converse Lyapunov function, i.e., one whose derivative along solutions can be used to establish the class- 𝒦ℒ estimate, exists if and only if the class- 𝒦ℒ estimate is robust, i.e., it holds for a larger, perturbed differential inclusion. It remains an open question whether...

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