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    Beurling algebra analogues of the classical theorems of Wiener and Levy on absolutely convergent Fourier series

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    Let ff be a continuous function on the unit circle Γ\Gamma, whose Fourier series is ω\omega-absolutely convergent for some weight ω\omega on the set of integers Z\mathcal{Z}. If ff is nowhere vanishing on Γ\Gamma, then there exists a weight ν\nu on Z\mathcal{Z} such that 1/f1/f had ν\nu-absolutely convergent Fourier series. This includes Wiener's classical theorem. As a corollary, it follows that if ϕ\phi is holomorphic on a neighbourhood of the range of ff, then there exists a weight χ\chi on Z\mathcal{Z} such that \hbox{ϕf\phi\circ f} has χ\chi-absolutely convergent Fourier series. This is a weighted analogue of L\'{e}vy's generalization of Wiener's theorem. In the theorems, ν\nu and χ\chi are non-constant if and only if ω\omega is non-constant. In general, the results fail if ν\nu or χ\chi is required to be the same weight ω\omega.Comment: 4 page

    Understanding and Improving the Wang-Landau Algorithm

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    We present a mathematical analysis of the Wang-Landau algorithm, prove its convergence, identify sources of errors and strategies for optimization. In particular, we found the histogram increases uniformly with small fluctuation after a stage of initial accumulation, and the statistical error is found to scale as lnf\sqrt{\ln f} with the modification factor ff. This has implications for strategies for obtaining fast convergence.Comment: 4 pages, 2 figures, to appear in Phys. Rev.
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