newbie alert: FindRoot

*To*: mathgroup at smc.vnet.net*Subject*: [mg49397] newbie alert: FindRoot*From*: schaa at geo.uni-koeln.de (Ralf Schaa)*Date*: Sat, 17 Jul 2004 06:39:23 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

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