利用拓扑度理论和不动点指数理论,研究了二阶非线性变系数奇异微分方程u″(t)+a(t)u(t)=r(t),(u(t))的周期解的存在性.特别地,本文没有假设a(t)和f(u)的非负性.
The existence of periodic solutions is investigated for second-order nonlinear singular differential equations with variable parameters u"(t) + a(t)u(t) = r(t)f(u(t)) by topological degree theory and fixed point index theory. In particular, the nonnegativity of a(t) and f(u) are not necessarily assumed.