Re: Is this possible? Residue computation leads to complexInfinity?

• To: mathgroup at smc.vnet.net
• Subject: [mg60735] Re: Is this possible? Residue computation leads to complexInfinity?
• From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
• Date: Mon, 26 Sep 2005 04:05:40 -0400 (EDT)
• Organization: The Open University, Milton Keynes, U.K.
• References: <dh5hl9\$dlc\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```kiki wrote:
> In[15]:=
> \!\(FullSimplify[Residue[\(\[ImaginaryI]\ z\)\/\(1 - \((2 + 4\ a)\)\ z\^2 +
> z\
> \^4\), \@\(a + 1\) - \@a], \ a > 0]\)
>
> Out[15]=
> \!\(Residue[ComplexInfinity, \(-\@a\) + \@\(1 + a\)]\)
>
>
The syntax is not correct. Try

In[1]:=
FullSimplify[Residue[(I*z)/(1 - (2 + 4*a)*z^2 + z^4),
{z, Sqrt[a + 1] - Sqrt[a]}], a > 0]

Out[1]=
(I*(-1 + Sqrt[1 + 1/a]))/(8*(-1 - a + Sqrt[a + a^2]))

Regards,
/J.M.

```

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