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Mathematical function
In mathematics , there are several functions known as Kummer's function . One is known as the confluent hypergeometric function of Kummer. Another one, defined below, is related to the polylogarithm . Both are named for Ernst Kummer .
Kummer's function is defined by
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{\displaystyle \Lambda _{n}(z)=\int _{0}^{z}{\frac {\log ^{n-1}|t|}{1+t}}\;dt.}
The duplication formula is
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{\displaystyle \Lambda _{n}(z)+\Lambda _{n}(-z)=2^{1-n}\Lambda _{n}(-z^{2})}
Compare this to the duplication formula for the polylogarithm:
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{\displaystyle \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
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{\displaystyle \operatorname {Li} _{n}(z)=\operatorname {Li} _{n}(1)\;\;+\;\;\sum _{k=1}^{n-1}(-1)^{k-1}\;{\frac {\log ^{k}|z|}{k!}}\;\operatorname {Li} _{n-k}(z)\;\;+\;\;{\frac {(-1)^{n-1}}{(n-1)!}}\;\left[\Lambda _{n}(-1)-\Lambda _{n}(-z)\right].}
References
Lewin, Leonard, ed. (1991), Structural Properties of Polylogarithms , Providence, RI: American Mathematical Society, ISBN 0-8218-4532-2 
![{\displaystyle \operatorname {Li} _{n}(z)=\operatorname {Li} _{n}(1)\;\;+\;\;\sum _{k=1}^{n-1}(-1)^{k-1}\;{\frac {\log ^{k}|z|}{k!}}\;\operatorname {Li} _{n-k}(z)\;\;+\;\;{\frac {(-1)^{n-1}}{(n-1)!}}\;\left[\Lambda _{n}(-1)-\Lambda _{n}(-z)\right].}](/media/api/rest_v1/media/math/render/svg/4f7490edccdcd619a70f975e7e86d638504572e0)
