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Re: computing residues

  • To: mathgroup at
  • Subject: [mg54902] Re: computing residues
  • From: Maxim <ab_def at>
  • Date: Sat, 5 Mar 2005 01:34:48 -0500 (EST)
  • References: <> <> <> <d09d9c$d4c$>
  • Sender: owner-wri-mathgroup at

On Fri, 4 Mar 2005 10:29:00 +0000 (UTC), Andrzej Kozlowski  
<akoz at> wrote:

> I have to admit Mathematica is smarter than I had thought and in fact:
> Residue[1/Sin[x],{x,Root[8*#1^3-6*#1-1&,3]-Cos[Pi/9]}]
> 1
> I made a mistake by using Root[8*#1^3-6*#1-1&,1] instead of
> Root[8*#1^3-6*#1-1&,3] in the first part of my example below. In fact
> Residue deals with this case impressively well. This certainly seems to
> reduce the strength  of my argument, though I still would prefer to get
> an unevaluated input in the non-numerical case.
> Andrzej

This is simply a case where Mathematica assumes sufficiently close values  
to be equal:

   {x, Root[8*#^3 - 6*# - 1&, 3] - Cos[Pi/9] + 10^-75}]


which is incorrect. Series and Limit make the same 'error of the second  

Maxim Rytin
m.r at

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