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In mathematics, the exponential integral Ei is a special function on the complex plane. It is defined as one particular definite integral of the ratio between an exponential function and its argument. ==Definitions== For real nonzero values of ''x'', the exponential integral Ei(''x'') is defined as : In general, a branch cut is taken on the negative real axis and E1 can be defined by analytic continuation elsewhere on the complex plane. For positive values of the real part of , this can be written〔Abramowitz and Stegun, p. 228, 5.1.4 with ''n'' = 1〕 : The behaviour of E1 near the branch cut can be seen by the following relation:〔Abramowitz and Stegun, p. 228, 5.1.7〕 : 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「exponential integral」の詳細全文を読む スポンサード リンク
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