Er’omenko V. O.
Quasiperiodic solutions of degenerate linear systems of second-order ordinary differential equations
Ukr. Mat. Zh. - 2010. - 62, № 6. - pp. 773–783
We establish sufficient conditions for the existence of quasiperiodic solutions of a system of ordinary second-order differential equations with degenerate symmetric matrix of the second derivatives for an arbitrary quasiperiodic inhomogeneity.
Periodic solutions of systems of two linear first-order ordinary differential equations with degenerate asymmetric matrix with derivatives
Ukr. Mat. Zh. - 1998. - 50, № 3. - pp. 350–356
We establish sufficient conditions for the existence of a periodic solution of a system of two linear firstorder ordinary differential equations with degenerate asymmetric matrix with derivatives in the case of an arbitrary periodic inhomogeneity.
Ukr. Mat. Zh. - 1997. - 49, № 8. - pp. 1137–1142
We consider a scalar linear second-order ordinary differential equation whose coefficient of the second derivative may change its sign when vanishing. For this equation, we obtain sufficient conditions for the existence of a periodic solution in the case of arbitrary periodic inhomogeneity.