Quasi-periodic oscillations in second-order systems via semilinear elliptic equations.
Résumé
To find quasi-periodic solutions to forced second-order ordinary differential equations we formulate boundary value problems on degenerate semilinear elliptic second-order partial differential equations. To solve these last problems we use a regularizatiopn method and variational tools. We establish an existence theorem of weak quasi-periodic solutions and a result of density for usual quasi-periodic solutions.