Re: newbie alert: FindRoot

*To*: mathgroup at smc.vnet.net*Subject*: [mg49429] Re: newbie alert: FindRoot*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Mon, 19 Jul 2004 07:46:26 -0400 (EDT)*Organization*: Universitaet Leipzig*References*: <cdb18e$ahd$1@smc.vnet.net>*Reply-to*: kuska at informatik.uni-leipzig.de*Sender*: owner-wri-mathgroup at wolfram.com

Hi, a _ (underscore) is used by Mathematica to specify a pattern and you can't use it in variable names Vt = 49.833666; Vr = 49.837507; Pt = 372331487.64643341; Pr = 5406.0310; Psit = 1.4213396; Psir = 2.0724097; Fdop = 363893.42; FindRoot[{Vt*Cos[Thetat] - Vr*Cos[Thetar] - Fdop == 0, Pt*Sin[Thetat - Psit] + a == 0, Pr*Sin[Thetar - Psir] + a == 0}, {Thetat, 0}, {Thetar, 10}, {a, 100}] Regards Jens Ralf Schaa wrote: > > Hi Folks, > > I am programming in IDL and I have this set of nonlinear equations, > which can be solved numerically in IDL with Broyden's method ... so > far so good. > Now, when i slightly vary the initial guess the solutions vary hugely. > > Now the question for the community: > I'd like to check my programming code with mathematica using the > FindRoot function like this: > > Vt := 49.833666; > Vr := 49.837507; > Pt := 372331487.64643341; > Pr := 5406.0310; > Psi_t := 1.4213396; > Psi_r := 2.0724097; > Fdop := 363893.42; > > FindRoot[ > {Vt*Cos[Theta_t] - Vr*Cos[Theta_r] - Fdop == 0, > Pt*Sin[Theta_t - Psi_t] + a == 0, > Pr*Sin[Theta_r - Psi_r] + a == 0}, > {Theta_t, 0}, {Theta_r, 0}, {a, 100}]; > > But all I get is something like this: > ... "is not a length 3 list of numbers at {Theta_t,Theta_r,a} = > {0.`,0.`,100.`}." > > So how has this to be done correctly ? > > Thanks in advance! > -Ralf