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In mathematics, Harnack's inequality is an inequality relating the values of a positive harmonic function at two points, introduced by . and generalized Harnack's inequality to solutions of elliptic or parabolic partial differential equations. Perelman's solution of the Poincaré conjecture uses a version of the Harnack inequality, found by , for the Ricci flow. Harnack's inequality is used to prove Harnack's theorem about the convergence of sequences of harmonic functions. Harnack's inequality can also be used to show the interior regularity of weak solutions of partial differential equations. ==The statement== Harnack's inequality applies to a non-negative function ''f'' defined on a closed ball in R''n'' with radius ''R'' and centre ''x''0. It states that, if ''f'' is continuous on the closed ball and harmonic on its interior, then for any point ''x'' with |''x'' - ''x''0| = ''r'' < ''R'' : In the plane R2 (''n'' = 2) the inequality can be written: : For general domains in the inequality can be stated as follows: If is a bounded domain with , then there is a constant such that for every twice differentiable, harmonic and nonnegative function . The constant is independent of ; it depends only on the domains and . 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「Harnack's inequality」の詳細全文を読む スポンサード リンク
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