2010/10/26 by A. M. Savchuk, Savchuk, A. M., A. A. Shkalikov +1
Mathematics · #34L40 #FOS: Mathematics #Spectral Theory (math.SP) #math.SP #msc:34L40
paper · pdf · doi:10.48550/arxiv.1010.5344
16 pages
arxiv created 2010/10/26 · arxiv updated 2010/10/27
Denote by LD the Sturm-Liouville operator Ly=-y" +q(x)y on the finite interval [0,π] with Dirichlet boundary conditions y(0)=y(π)=0. Let \λk\1^∞ and \αk\1^∞ be the sequences of the eigenvalues and norming constants of this operator. For all θ\geqslant 0 we study the map F: W2θ → lDθ defined by F(σ) =\sk\1^∞. Here σ= ∫ q is the primitive of q, \bold s = \sk\1^∞ be regularized spectral data defined by s2k =√(λk)-k, s2k-1=αk-π/2 and lDθ are special Hilbert spaces which are constructed in the paper as finite dimensional extensions of the usual weighted l2 spaces. We give a complete characterization of the image of this nonlinear operator, show that it is locally invertible analytic map, find explicit form of its Frechet derivative. The main result of the paper are the uniform estimates of the form ‖σ-σ1‖θ\asymp ‖\bold s -\bold s1‖θ, provided that the spectral data \bold s and \bold s1 run through special convex sets in the spaces lDθ.