       Re: NDSolve help

• To: mathgroup at smc.vnet.net
• Subject: [mg43647] Re: NDSolve help
• From: sean_incali at yahoo.com (sean kim)
• Date: Sat, 27 Sep 2003 04:58:09 -0400 (EDT)
• References: <bl0uk1\$3vm\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```sashan <mabus at operamail.com> wrote in message news:<bl0uk1\$3vm\$1 at smc.vnet.net>...
> I'm a newb to mathematica. I'm trying to use NDSolve for a system of 2
> 2nd order ODE's and it complains that the number of initial conditions
> (4) is not equal to the total order of the system (2). But I'm pretty
> sure I've specified all the initial conditions. I've pasted the NDSolve
> code I'm trying to write.
>
> \!\(\(solution\  = \ NDSolve[{\(y''\)[t] == \(-\((\(-\ x[
>         t]^2\) + y[t]\ v^2)\)\), \ \(x''\)[
>                 t] == \(-\((\ x[t] y[t] + x[t] v^2)\)\),
>                      y == 0, \(y'\) == \(-1\), x[
>             0] == 1, \(x'\) == 0} /.
>               v -> \@\(\(x'\)[t]^2 + \(y'\)[t]^2\), {x, y}, {t, 0,
> 200}];\)\)

I can't seem to recreate the problem in Mathematica 5.0 you can use InputForm
to change those symbols to ascii inputform.  your problem is as pasted
below

In:=
solution =
NDSolve[{Derivative[y][t]\[Equal]x[t]^2-v^2*y[t],
Derivative[x][t]\[Equal]-(v^2*x[t])-x[t]*y[t],y\[Equal]0,
Derivative[y]\[Equal]-1,x\[Equal]1,
Derivative[x]\[Equal]0}/.v\[Rule]
Sqrt[Derivative[x][t]^2+Derivative[y][t]^2],{x,y},{t,0,200}]
Out=
{{x\[Rule]InterpolatingFunction[{{0.,200.}},<>],
y\[Rule]InterpolatingFunction[{{0.,200.}},<>]}}

as I said. no errors on Mathematica 5.0  I wonder what the problem is...

```

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