Re: replicating variables
- To: mathgroup at smc.vnet.net
- Subject: [mg43690] Re: replicating variables
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Tue, 30 Sep 2003 16:42:38 -0400 (EDT)
- Organization: Universitaet Leipzig
- References: <bl8hci$8d6$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
I hope you are able to enter the equations in the
*correct* Mathematica syntax
sol = NDSolve[{
a'[t] == a[t] (3 - 2 b[t] - a[t]),
b'[t] == b[t] (2 - a[t] - b[t]),
a[0] == 2, b[0] == 1}, {a[t], b[t]}, {t, 0,
20}]
ParametricPlot[Evaluate[{a[t], b[t]} /. sol[[1]]], {t, 0, 20}]
and
ParametricPlot3D[Evaluate[{t, a[t], b[t]} /. sol[[1]]], {t, 0, 20},
BoxRatios -> {1, 1, 1}]
will help you.
Regards
Jens
Young Kim wrote:
>
> Hi,
>
> Let's say I have two non linear differential equations which cannot be
> analytically solved,
> for example,
>
> a[t]' == a[t] { 3 - 2 b[t] - a[t] }
> b[t]' == b[t] { 2 - a[t] - b[t] }
>
> What do I need to do if I want to draw parametric curve of
> r[t] = { a[t], b[t] }, or { a[t], b[t], t } in 3D where a[t] , b[t]
> are the numerical solutions of the preceding equations.
> Thanks.
>
> Young
>
>