Exact multiplicity of solutions to superlinear and sublinear problems
نویسنده
چکیده
(f2) lim u→∞ f(u) u =f+ ¿ 0; lim u→−∞ f(u) u =f− ¿ 0: For the de5niteness, we assume f+ ¿f−, and when f+ =f−, we use f± to represent it. We will consider f being either superlinear or sublinear. f is said to be superlinear if f(u)=u is decreasing in (0;∞) and is increasing in (−∞; 0); and f is said to be sublinear if f(u)=u is increasing in (0;∞) and is decreasing in (−∞; 0): The semilinear equation (1.1) with f satisfying (f1), (f2) has been studied extensively since early 1970s. Several di9erent approaches, like variational methods (Morse
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