       Re: Hypergeometric1F1 polynomial

• To: mathgroup at smc.vnet.net
• Subject: [mg91476] Re: Hypergeometric1F1 polynomial
• From: "Alec Mihailovs" <alec at mihailovs.com>
• Date: Sat, 23 Aug 2008 01:41:29 -0400 (EDT)
• References: <g8je5u\$a4n\$1@smc.vnet.net> <g8lpat\$ijd\$1@smc.vnet.net>

```Maxim Rytin wrote

> Here's one way to obtain the correct answer. The intermediate steps
> are only formally correct but in the end the singularities cancel out:
>
> In:= Sum[
>   Binomial[n, k] (2 x)^k/(Binomial[2 n, k] k!) // FunctionExpand //
>    # /. Gamma[a_ - k] :> (-1)^k Pi Csc[a Pi]/Gamma[1 - a + k]&,
>   {k, 0, n}] //
>  FullSimplify // Simplify[#, Element[n, Integers]]&
>
> Out= 1/Gamma[1/2 + n] 2^-n ((-2)^n E^x Pi
> Hypergeometric0F1Regularized[1/2 - n, x^2/4] + Sqrt[Pi] (-x)^(1 + n)
> HypergeometricPFQRegularized[{1, 1}, {1 - n, 2 + n}, 2 x])

That seems to be correct answer. It is an interesting way of obtaining it.

Is there a way to simplify it to one of 2 other forms of the correct answer
that I mentioned in the original post?

Alec

```

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