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MathGroup Archive 2005

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Re: Question on General::nlnum warning when use FindRoot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55152] Re: Question on General::nlnum warning when use FindRoot
  • From: Peter Pein <petsie at arcor.de>
  • Date: Mon, 14 Mar 2005 03:44:00 -0500 (EST)
  • References: <d114mo$e1k$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

PengYu.UT at gmail.com wrote:

> Hi All,
> 
> When I use FindRoot to solve an equation, I always get the warning
> General::nlnum. Do you have any idea what this warning refers to? The
> mathematical help says "Notes for this message have not yet been
> added." What function I should use to solve that equation numerically?
> Thanks!
> 
> Best wishes,
> Peng
> 
> intensity[x_, δ_, p_, λ_] := 1/4 + (2*Cos[(Pi*x)/100])/Pi +
> (4*Cos[(Pi*x)/100]^2)/Pi^2 - (2*Cos[(3*Pi*x)/100])/(3*Pi) -
>  (8*Cos[(Pi*x)/100]*Cos[(3*Pi*x)/100])/(3*Pi^2) +
> (4*Cos[(3*Pi*x)/100]^2)/(9*Pi^2)
> 
> FindRoot[intensity[50, δ, 200, 50] == 0.3*(1/4 + 32/(9*Pi^2) +
> (4*Sqrt[2])/(3*Pi))*1.1, {δ, 1}]
> 
your equation is independent of delta (it holds for uncommon values of
Pi: Pi==(8/201)*(33*Sqrt[2] - 10*Sqrt[66]) or Pi==(8/201)*(33*Sqrt[2] +
10*Sqrt[66]) ;-) ). You could have written FindRoot[False,{\[Delta],1}]
instead - and False is indeed "not a list of numbers".

-- 
Peter Pein
Berlin


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