       • 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 ?