AN APPROXIMATION APPROACH TO EIGENVALUE INTERVALS FOR SINGULAR BOUNDARY VALUE PROBLEMS WITH SIGN CHANGING NONLINEARITIES

This paper presents new existence results for the singular boundary value problem −u = g(t,u )+ λh(t,u), t ∈ (0,1) u(0 )= 0 = u(1). In particular our nonlinearity may be singular at t = 0, 1a ndu = 0 and is allowed to change sign. Existence in this paper will be established by obtaining a sequence of upper and lower solutions which in turn will generate a sequence of approximate solutions.