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In mathematics, quasi-isometry is an equivalence relation on metric spaces that ignores their small-scale details in favor of their coarse structure. The concept is especially important in Gromov's geometric group theory.〔 〕 ==Definition== Suppose that is a (not necessarily continuous) function from one metric space to a second metric space . Then is called a ''quasi-isometry'' from to if there exist constants , , and such that the following two properties both hold:〔P. de la Harpe, ''Topics in geometric group theory''. Chicago Lectures in Mathematics. University of Chicago Press, Chicago, IL, 2000. ISBN 0-226-31719-6〕 #For every two points and in , the distance between their images is (up to the additive constant ) within a factor of of their original distance. More formally: #: #Every point of is within the constant distance of an image point. More formally: #: The two metric spaces and are called quasi-isometric if there exists a quasi-isometry from to . 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「Quasi-isometry」の詳細全文を読む スポンサード リンク
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