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Tento článek ukazuje možné použití Floquetovy teorie v otázce ljapunovské stability lineárních diferenciálních rovnic druhého řádu s periodickými koeficienty. Jsou uvedeny obecné věty o stabilitě řešení uvažovaných rovnic v řeči Floquetových multiplikátorů, které jsou následně využity v důkazech jednoduchých efektivních kritérií. Je také vysvětlena souvislost mezi Ljapunovovými a Floquetovými charakteristickými exponenty a ukázáno použití těchto pojmů mimo jiné v otázce stability rovnovážného stavu...

We study the existence and uniqueness of a positive solution to the problem $$u^{\text{'}\text{'}}=p\left(t\right)u+q(t,u)u+f\left(t\right);u\left(0\right)=u\left(\omega \right),u^{\text{'}}\left(0\right)=u^{\text{'}}\left(\omega \right)$$ with a super-linear nonlinearity and a nontrivial forcing term $f$. To prove our main results, we combine maximum and anti-maximum principles together with the lower/upper functions method. We also show a possible physical motivation for the study of such a kind of periodic problems and we compare the results obtained with the facts well known for the corresponding autonomous case.

We discuss Lyapunov stability/instability of both lower and upper equilibria of free damped pendulum with periodically oscillating suspension point. We recall the results of Bogolyubov and Kapitza, provide new effective criteria of stability/instability of the equilibria of pendulum equation, and give the exact and complete proofs. The criteria obtained are formulated in terms of positivity/negativity of Green's functions of the periodic boundary value problems for linearized equations. Furthermore,...

We establish new efficient conditions sufficient for the unique solvability of the initial value problem for two-dimensional systems of linear functional differential equations with monotone operators.

Some Wintner and Nehari type oscillation criteria are established for the second-order linear delay differential equation.

We study the question of the existence, uniqueness, and continuous dependence on parameters of the Carathéodory solutions to the Cauchy problem for linear partial functional-differential equations of hyperbolic type. A theorem on the Fredholm alternative is also proved. The results obtained are new even in the case of equations without argument deviations, because we do not suppose absolute continuity of the function the Cauchy problem is prescribed on, which is rather usual assumption in the existing...

Nonimprovable, in a certain sense, sufficient conditions for the unique solvability of the boundary value problem $$u^{\text{'}}\left(t\right)=\ell \left(u\right)\left(t\right)+q\left(t\right),u\left(a\right)+\lambda u\left(b\right)=c$$ are established, where $\ell :C\left(\right[a,b];R)\to L\left(\right[a,b];R)$ is a linear bounded operator, $q\in L\left(\right[a,b];R)$, $\lambda \in R_{+}$, and $c\in R$. The question on the dimension of the solution space of the homogeneous problem $$u^{\text{'}}\left(t\right)=\ell \left(u\right)\left(t\right),u\left(a\right)+\lambda u\left(b\right)=0$$ is discussed as well.

Nonimprovable sufficient conditions for the solvability and unique solvability of the problem $$u^{\text{'}}\left(t\right)=F\left(u\right)\left(t\right),u\left(a\right)-\lambda u\left(b\right)=h\left(u\right)$$ are established, where $F:\to$ is a continuous operator satisfying the Carathèodory conditions, $h:\to R$ is a continuous functional, and $\lambda \in$.