       Re: replicating variables

• To: mathgroup at smc.vnet.net
• Subject: [mg43688] Re: [mg43683] replicating variables
• From: sean kim <sean_incali at yahoo.com>
• Date: Tue, 30 Sep 2003 16:42:36 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```a few things.

1. mathematica syntax.

curly brackets are used for lists. parenthesis is used
for groupings.

and ' needs tocome before the independent variable in
derivative definition. as a'[t] not a[t]'

which these fixed, your equation will output a
interpolatign functions but it doesn't seem much.

it's probably due to the iniaitla conditions and
parameter choices.

nlde = {a'[t] == a[t] (3 - 2 b[t] - a[t]), b'[t] ==
b[t] (2 - a[t] - b[t])}

nldeics = Join[nlde, {a == 0, b == 1}]

sol = NDSolve[ nldeics, {a[t], b[t]}, {t, 0, 1}]

ParametricPlot[Evaluate[{a[t], b[t]} /. sol], {t, 0,
1}];

good luck

sean

--- Young Kim <kim17 at fas.harvard.edu> 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
>
>
>

=====
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