       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_, Î´_, p_, Î»_] := 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, Î´, 200, 50] == 0.3*(1/4 + 32/(9*Pi^2) +
> (4*Sqrt)/(3*Pi))*1.1, {Î´, 1}]
>
your equation is independent of delta (it holds for uncommon values of
Pi: Pi==(8/201)*(33*Sqrt - 10*Sqrt) or Pi==(8/201)*(33*Sqrt +
10*Sqrt) ;-) ). 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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