The geometry of the critical set of nonlinear periodic Sturm–Liouville operators (original) (raw)

2009, Journal of Differential Equations

We study the critical set C of the nonlinear differential operator F (u) = −u ′′ + f (u) defined on a Sobolev space of periodic functions H p (S 1 ), p ≥ 1. Let R 2 xy ⊂ R 3 be the plane z = 0 and, for n > 0, let ⊲⊳ n be the cone x 2 + y 2 = tan 2 z, |z − 2πn| < π/2; also set Σ = R 2 xy ∪ n>0 ⊲⊳ n . For a generic smooth nonlinearity f : R → R with surjective derivative, we show that there is a diffeomorphism between the pairs (H p (S 1 ), C) and (R 3 , Σ) × H where H is a real separable infinite dimensional Hilbert space.

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Critical sets of nonlinear Sturm-Liouville operators of Ambrosetti-Prodi type

Nonlinearity

The critical set C of the operator F:H^2_D([0,pi]) -> L^2([0,pi]) defined by F(u)=-u''+f(u) is studied. Here X:=H^2_D([0,pi]) stands for the set of functions that satisfy the Dirichlet boundary conditions and whose derivatives are in L^2([0,pi]). For generic nonlinearities f, C=\cup C_k decomposes into manifolds of codimension 1 in X. If f''<0 or f''>0, the set C_j is shown to be non-empty if, and only if, -j^2 (the j-th eigenvalue of u -> u'') is in the range of f'. The critical components C_k are (topological) hyperplanes. Comment: 6 pages, no figures

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Progress in Nonlinear Differential Equations and Their Applications, 2006

We survey recent work of Burghelea, Malta and both authors on the topology of critical sets of nonlinear ordinary differential operators. For a generic nonlinearity f , the critical set of the first order nonlinear operator

The topology of critical sets of some ordinary difierential operators

2000

We survey recent work of Burghelea, Malta and both authors on the topology of critical sets of nonlinear ordinary difierential operators. For a generic nonlinearity f, the critical set of the flrst order nonlinear operator F1(u)(t) = u0(t) + f(u(t)) acting on the Sobolev space H1 p of periodic functions is either empty or ambient difieomorphic to a hyperplane. For

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Journal of Functional Analysis, 1991

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