Solvability of generalized third order coupled systems with two-point boundary conditions

Abstract

In this paper we consider the nonlinear third order coupled system composed by the differential equations -u′′′(t)=f(t,u(t),u′(t),u′′(t),v(t),v′(t),v′′(t)) -v′′′(t)=h(t,u(t),u′(t),u′′(t),v(t),v′(t),v′′(t)), </K1.1> with f,h:[0,1]×ℝ⁶→ℝ continuous functions, and the boundary conditions u(0)=u′(0)=u′(1)=0 v(0)=v′(0)=v′(1)=0.

We remark that the nonlinearities can depend on all derivatives of both unknown functions, which is new in the literature, as far as we know. This is due to an adequate auxiliary integral problem with a truncature, applying lower and upper solutions method with bounded perturbations. The main theorem is an existence and localization result, which provides some qualitative data on the system solution, such as, sign, variation, bounds,..., as it can be seen in the example.