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In mathematics, in the field of harmonic analysis, the van der Corput lemma is an estimate for oscillatory integrals named after the Dutch mathematician J. G. van der Corput. The following result is stated by E. Stein:〔Elias Stein, ''Harmonic Analysis: Real-variable Methods, Orthogonality and Oscillatory Integrals''. Princeton University Press, 1993. ISBN 0-691-03216-5〕 Suppose that a real-valued function is smooth in an open interval , and that for all . Assume that either , or that and is monotone for . There is a constant , which does not depend on , such that : for any . ==Sublevel set estimates== The van der Corput lemma is closely related to the sublevel set estimates (see for example 〔M. Christ, ''Hilbert transforms along curves'', Ann. of Math. 122 (1985), 575--596〕), which give the upper bound on the measure of the set where a function takes values not larger than . Suppose that a real-valued function is smooth on a finite or infinite interval , and that for all . There is a constant , which does not depend on , such that for any the measure of the sublevel set is bounded by . 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「Van der Corput lemma (harmonic analysis)」の詳細全文を読む スポンサード リンク
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