Re: A question about numerically solving differential equations

• To: mathgroup at smc.vnet.net
• Subject: [mg130328] Re: A question about numerically solving differential equations
• From: Bob Hanlon <hanlonr357 at gmail.com>
• Date: Wed, 3 Apr 2013 04:09:22 -0400 (EDT)
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• References: <kirks3\$at8\$1@smc.vnet.net>

```a has to have a numeric value

Manipulate[
Plot[
Evaluate[{
Tooltip[f0[r], "f0"],
Tooltip[f1[r], "f1"]} /.
NDSolve[{
2 f0'[r]/r + f0''[r] ==
-2 a f1[r]/r^4 + 2 a f1'[r]/r^3,
-2 f1[r]/r^2 + 2 f1'[r]/r + f1''[r] ==
2 a f0'[r]/r^3,
f0[1] == 1, f1[1] == 1,
f0[2] == 1, f1[2] == 1},
{f0[r], f1[r]}, {r, 1, 2}]],
{r, 1, 2},
PlotRange -> {0.6, 1.4}],
{a, -10, 10, Appearance -> "Labeled"}]

Bob Hanlon

On Tue, Apr 2, 2013 at 3:26 AM, debguy <johnandsara2 at cox.net> wrote:

> 2 D[f0[r], r]/r + D[f0[r], r, r] == -2 A f1[r]/r^4 +  2 A D[f1[r], r]/
> r^3
> -2 f1[r]/r^2 + 2 D[f1[r], r]/r + D[f1[r], r, r] == 2 A D[f0[r], r]/
> r^3
>
> I tried it later.  I cannot get anything
>           y`[x]==g`[x]==y[x]==g[x]
> to work using any conditions i try.
>
> NDSOlve[{ y`[x]==g[x], g`[x]==g[x]+y[x], g[1]=1, y[1]=1 },{y,g},{x,
> 1,2} ]  (* foo *)
>
> Is the only form I can get to work using two funs.  Which is what the
> book example uses.
>
> I'm unsure how to re-express your eq'n that way to try it.
>
>

```

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