Forced singular oscillators and the method of lower and upper solutions
Forced singular oscillators and the method of lower and upper solutions
In this note, we study the existence of positive periodic solutions of the second order differential equation $$ u''+g(u)u'+f(t,u)=h(t) $$ where $f(t,\cdot)$ has a singularity of repulsive type at the origin. We use the method of lower and upper solutions.