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MathGroup Archive 2003

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Re: Log Equation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg44800] Re: Log Equation
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 27 Nov 2003 11:38:24 -0500 (EST)
  • Organization: Universitaet Leipzig
  • References: <bpuqjf$o65$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

Mathematica *can* solve the equations in terms of the PolyLog[]
function

http://functions.wolfram.com/ZetaFunctionsandPolylogarithms/PolyLog/

and if someone use Mathematica he don't need a numerical method
for it.

Regards
  Jens

Florian Jaccard wrote:
> 
> Yes, the équation you want to solve is transcendental, so the only ways to
> solve it are numerical.
> 
> The most simple way is to use FindRoot.
> But first, don't forget to draw f(x)=(1-x)/Log(x)-y ! You have to see an
> approximation of the root you are searching !
> 
> For example, let y = -2  :
> 
> In[1]:= Plot[(1 - x)/Log[x] + 2, {x, 0, 10},PlotRange -> {-4, 4}];
> 
> In[2]:= FindRoot[(1 - x)/Log[x] == -2, {x, 2}]
> 
> Meilleures salutations
> 
> Florian Jaccard
> 
> -----Message d'origine-----
> De : Bernard Bourée [mailto:bernard at bouree.net]
> Envoyé : lun., 24. novembre 2003 06:05
> À : mathgroup at smc.vnet.net
> Objet :  Log Equation
> 
> I 'm trying to find a way to solve the equation
> 
> y = (1-x)/ Log(x)
> 
> How can I find x when y is known ?
> 
> Is there a numerical method ?
> with series development?
> 
> --
> Bernard Bourée
> bernard at bouree.net


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