• 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>
• 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 ?
>