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In mathematics, the Pettis integral or Gelfand–Pettis integral, named after I. M. Gelfand and B. J. Pettis, extends the definition of the Lebesgue integral to vector-valued functions on a measure space, by exploiting duality. The integral was introduced by Gelfand for the case when the measure space is an interval with Lebesgue measure. The integral is also called the weak integral in contrast to the Bochner integral, which is the strong integral. ==Definition== Suppose that , where is a measure space and is a topological vector space. Suppose that admits a dual space that separates points. e.g., a Banach space or (more generally) a locally convex, Hausdorff vector space. We write evaluation of a functional as duality pairing: . Choose any measurable set . We say that is Pettis integrable (over ) if there exists a vector so that : In this case, we call the Pettis integral of (over ). Common notations for the Pettis integral include , and . A function is Pettis integrable (over ) if the scalar-valued function is integrable for every functional . 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「Pettis integral」の詳細全文を読む スポンサード リンク
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