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In mathematics, the Dini and Dini-Lipschitz tests are highly precise tests that can be used to prove that the Fourier series of a function converges at a given point. These tests are named after Ulisse Dini and Rudolf Lipschitz. == Definition == Let ''f'' be a function on (), let ''t'' be some point and let δ be a positive number. We define the local modulus of continuity at the point ''t'' by : Notice that we consider here ''f'' to be a periodic function, e.g. if ''t'' = 0 and ε is negative then we ''define'' ''f''(ε) = ''f''(2π + ε). The global modulus of continuity (or simply the modulus of continuity) is defined by : With these definitions we may state the main results ''Theorem (Dini's test): Assume a function f satisfies at a point t that'' : ''Then the Fourier series of f converges at t to f(t).'' For example, the theorem holds with but does not hold with . ''Theorem (the Dini-Lipschitz test): Assume a function f satisfies'' : ''Then the Fourier series of f converges uniformly to f.'' In particular, any function of a Hölder class satisfies the Dini-Lipschitz test. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Dini test」の詳細全文を読む スポンサード リンク
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