Czechoslovak Mathematical Journal, Vol. 54, No. 2, pp. 347-371, 2004

Existence of solutions and of multiple solutions
for nonlinear nonsmooth periodic systems

Evgenia H. Papageorgiou, Nikolaos S. Papageorgiou

National Technical University, Department of Mathematics, Zografou Campus, Athens 15780, Greece, e-mail: npapg@math.ntua.gr

Abstract: In this paper we examine nonlinear periodic systems driven by the vectorial $p$-Laplacian and with a nondifferentiable, locally Lipschitz nonlinearity. Our approach is based on the nonsmooth critical point theory and uses the subdifferential theory for locally Lipschitz functions. We prove existence and multiplicity results for the "sublinear" problem. For the semilinear problem (i.e. $p = 2$) using a nonsmooth multidimensional version of the Ambrosetti-Rabinowitz condition, we prove an existence theorem for the "superlinear" problem. Our work generalizes some recent results of Tang (PAMS 126(1998)).

Keywords: $p$-Laplacian, nonsmooth critical point theory, Clarke subdifferential, saddle point theorem, periodic solution, Poincare-Wirtinger inequality, Sobolev inequality, nonsmooth Palais-Smale condition

Classification (MSC 2000): 34C25


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