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Coupled fixed points of nonlinear operators with applications. (English) Zbl 0635.47045
Let D be a subset of a real Banach space E, which is partially ordered by a cone P of E. The operator A:D×DE is mixed monotone if A(x,y) is nondecreasing in x and nonincreasing in y. The point (x’,y’) in D×D is a coupled fixed point of A if A(x ' ,y ' )=x ' and A(y ' ,x ' )=y ' . This extends the notion of fixed point z, for which A(z,z)=z. The authors prove existence theorems for coupled fixed points both for continuous and discontinuous A. Applications include the existence of solutions of initial value problems for some systems of ordinary differential equations with discontinuous right hand side.
Reviewer: I.N.Baker

MSC:
47H10Fixed point theorems for nonlinear operators on topological linear spaces
47H07Monotone and positive operators on ordered topological linear spaces
34G10Linear ODE in abstract spaces