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In mathematics, the Bishop–Gromov inequality is a comparison theorem in Riemannian geometry, named after Richard L. Bishop and Mikhail Gromov. It is closely related to Myers' theorem, and is the key point in the proof of Gromov's compactness theorem. ==Statement== Let be a complete ''n''-dimensional Riemannian manifold whose Ricci curvature satisfies the lower bound : for a constant . Let be the complete ''n''-dimensional simply connected space of constant sectional curvature (and hence of constant Ricci curvature ); thus is the ''n''-sphere of radius if ''K'' > 0, or ''n''-dimensional Euclidean space if , or an appropriately rescaled version of ''n''-dimensional hyperbolic space if . Denote by ''B''(''p'', ''r'') the ball of radius ''r'' around a point ''p'', defined with respect to the Riemannian distance function. Then, for any and , the function : is non-increasing on (0, ∞). As ''r'' goes to zero, the ratio approaches one, so together with the monotonicity this implies that : This is the version first proved by Bishop,〔Bishop, R. A relation between volume, mean curvature, and diameter. Amer. Math. Soc. Not. 10 (1963), p. 364.〕〔Bishop R.L., Crittenden R.J. Geometry of manifolds, Corollary 4, p. 256〕 originally assuming the (unnecessary) added hypothesis that is less than the injectivity radius at . 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「Bishop–Gromov inequality」の詳細全文を読む スポンサード リンク
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