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[2])/(3*Pi))*1.1, {Î´, 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