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An approximation for zero-balanced Appell function $F_1$ near $(1,1)$

D. Karp
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Abstract

We suggest an approximation for the zero-balanced Appell hypergeometric function $F_1$ near the singular point $(1,1)$. Our approximation can be viewed as a generalization of Ramanujan's approximation for zero-balanced ${_2F_1}$ and is expressed in terms of ${_3F_2}$. We find an error bound and prove some basic properties of the suggested approximation which reproduce the similar properties of the Appell function. Our approximation reduces to the approximation of Carlson-Gustafson when the Appell function reduces to the first incomplete elliptic integral.

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BibTeXRIS

D. Karp. 2007-01-19. An approximation for zero-balanced Appell function $F_1$ near $(1,1)$. https://doi.org/10.1016/j.jmaa.2007.07.071

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