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In mathematics, a pseudometric or semi-metric space〔Dmitri Burago, Yu D Burago, Sergei Ivanov, A Course in Metric Geometry, American Mathematical Society, 2001, ISBN 0-8218-2129-6.〕 is a generalized metric space in which the distance between two distinct points can be zero. In the same way as every normed space is a metric space, every seminormed space is a pseudometric space. Because of this analogy the term semimetric space (which has a different meaning in topology) is sometimes used as a synonym, especially in functional analysis. When a topology is generated using a family of pseudometrics, the space is called a gauge space. ==Definition== A pseudometric space is a set together with a non-negative real-valued function (called a pseudometric) such that, for every , #. # (''symmetry'') # (''subadditivity''/''triangle inequality'') Unlike a metric space, points in a pseudometric space need not be distinguishable; that is, one may have for distinct values . 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「Pseudometric space」の詳細全文を読む スポンサード リンク
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