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In mathematical analysis, the Minkowski inequality establishes that the L''p'' spaces are normed vector spaces. Let ''S'' be a measure space, let 1 ≤ ''p'' ≤ ∞ and let ''f'' and ''g'' be elements of L''p''(''S''). Then ''f'' + ''g'' is in L''p''(''S''), and we have the triangle inequality : with equality for 1 < ''p'' < ∞ if and only if ''f'' and ''g'' are positively linearly dependent, i.e., ''f'' = ''λg'' for some ''λ'' ≥ 0 or ''g'' = 0. Here, the norm is given by: : if ''p'' < ∞, or in the case ''p'' = ∞ by the essential supremum : The Minkowski inequality is the triangle inequality in L''p''(''S''). In fact, it is a special case of the more general fact : where it is easy to see that the right-hand side satisfies the triangular inequality. Like Hölder's inequality, the Minkowski inequality can be specialized to sequences and vectors by using the counting measure: : for all real (or complex) numbers ''x''1, ..., ''x''''n'', ''y''1, ..., ''y''''n'' and where n is the cardinality of S (the number of elements in S). ==Proof== First, we prove that ''f''+''g'' has finite ''p''-norm if ''f'' and ''g'' both do, which follows by : Indeed, here we use the fact that is convex over (for ) and so, by the definition of convexity, : This means that : Now, we can legitimately talk about . If it is zero, then Minkowski's inequality holds. We now assume that is not zero. Using the triangle inequality and then Hölder's inequality, we find that : We obtain Minkowski's inequality by multiplying both sides 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「Minkowski inequality」の詳細全文を読む スポンサード リンク
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