Saddle connections and subharmonics are investigated for a class of forced second order differential equations which have a fixed saddle point. In these equations, which have linear damping and a nonlinear restoring term, the amplitude of the forcing term depends on displacement in the system. Saddle connections are significant in nonlinear systems since their appearance signals a homoclinic bifurcation. The approach uses a singular perturbation method which has a fairly broad application to saddle connections and also to various subharmonics. The singular perturbation is unusual in that it uses a time-scale which has to be constructed over an infinite interval. The system with a cubic restoring term and a quadratic amplitude is looked at in some detail.

1980 Mathematics Subject Classification (1985 revision): 34D15, 58F22.