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In mathematics, the trigamma function, denoted , is the second of the polygamma functions, and is defined by : . It follows from this definition that : where is the digamma function. It may also be defined as the sum of the series : making it a special case of the Hurwitz zeta function : Note that the last two formulæ are valid when is not a natural number. ==Calculation== A double integral representation, as an alternative to the ones given above, may be derived from the series representation: : using the formula for the sum of a geometric series. Integration by parts yields: : An asymptotic expansion as a ウィキペディア(Wikipedia)』 ■ウィキペディアで「trigamma function」の詳細全文を読む スポンサード リンク
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