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Kummer's function

In mathematics, there are several functions known as Kummer's function. One is known as the confluent hypergeometric function of Kummer and E. T. Whittaker. Another one, defined below, is related to the polylogarithm. Both are named for Ernst Kummer.

Kummer's function is defined by

$\Lambda_n(z)=\int_0^z \frac{\log^{n-1}|t|}{1+t}\;dt.$

The duplication formula is

Λ n (z) + Λ n ( - z) = 2 1 - n Λ n ( - z 2)

Compare this to the duplication formula for the polylogarithm:

$\operatorname{Li}_n(z)+\operatorname{Li}_n(-z)= 2^{1-n}\operatorname{Li}_n(z^2).$

An explicit link to the polylogarithm is given by

$\operatorname{Li}_n(z)=\operatorname{Li}_n(1)\;\;+\;\; \sum_{k=1}^{n-1} (-)^{k-1} \;\frac{\log^k |z|} {k!} \;\operatorname{Li}_{n-k} (z) \;\;+\;\; \frac{(-)^{n-1}}{(n-1)!} \;\left[ \Lambda_n(-1) - \Lambda_n(-z) \right].$

References

Leonard Lewin (Ed.). Structural Properties of Polylogarithms (1991) Providence, RI: American Mathematical Society, Providence RI. ISBN 0-8218-4532-2

Categories: Special functions

Last updated: 05-27-2005 20:30:41

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12-03-2008 10:22:39
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