AN EXISTENCE PRINCIPLE FOR SOLUTIONS TO A SINGULAR BOUNDARY-VALUE PROBLEMS

摘要

The singular boundary-value problemju" + g{t,u,u') = 0 for t∈(O,l), u(0) =u(l) = 0is studied. The singularity may appear at u = 0, and the function g may change sign. An existence theorem for solutions to the above boundary-value problem is proposed, and it is proved via the method of upper and lower solutions.