Modified Prüfer and EFGP Transforms and Deterministic Models with Dense Point Spectrum

Abstract

We provide a new proof of the theorem of Simon and Zhu that in the region |E|<λ for a.e. energies, −(d^2/dx^2)+λ cos(x^α), 0<α<1 has Lyapunov behavior with a quasi-classical formula for the Lyapunov exponent. We also prove Lyapunov behavior for a.e.E∈[−2, 2] for the discrete model with V(j^2)=e^j,V(n)=0 if n∉ {1, 4, 9,…}. The arguments depend on a direct analysis of the equations for the norm of a solution.

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