# method for getting function from power series/perturbation series

is there any definite method or algorithm,software to get exact function or expression from series.e.g we get series solution of differential equation and we want exact expression rather than approximation series ?

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Usually I do this the other way around. I have a power series, and want its sum, so if I can find a DE it satisfies, then solve the DE to get the result! – Gerald Edgar Sep 11 '11 at 12:50

## 1 Answer

In some cases yes, see:

http://www.reduce-algebra.com/docs/qsum.pdf

and references therein...

EDIT A canonical reference is Petkovsek-Zeiberger's A=B.

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thanks very much, i would like to see more such stuff – anksh Sep 11 '11 at 6:41
More stuff in Wilf's book generatingfunctionology – Gerald Edgar Sep 11 '11 at 12:49