Re: Error with NDSolve

• To: mathgroup at smc.vnet.net
• Subject: [mg50976] Re: Error with NDSolve
• From: mathma18 at hotmail.com (Narasimham G.L.)
• Date: Thu, 30 Sep 2004 04:52:30 -0400 (EDT)
• References: <200409280458.AAA23991@smc.vnet.net> <cjdq6g\$ass\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```DrBob <drbob at bigfoot.com> wrote in message news:<cjdq6g\$ass\$1 at smc.vnet.net>...
> NDSolve[{si2'[t] == 2, si2[0] == 0, th2'[t] == Sin[si2[t]]/r2[t], th2[
>        0] == 0, r2'[t] == Cos[si2[t]], r2[0] == 1}, {si2, r2, th2}, {
>        t, 0, 25}];

> r[t_] = r2[t] /. First[%]
> th[t_] = th2[t] /. First[%%]
> si[t_] = si2[t] /. First[%%%]

Above three lines have some problem,but next two schemes work fine, Thanks.

> solution = First@
>      NDSolve[{si2'[t] == 2, si2[0] ==
>          0, th2'[t] == Sin[si2[t]]/r2[t], th2[0] == 0, r2'[t] ==
>            Cos[si2[t]], r2[0] == 1}, {si2, r2, th2}, {t, 0, 25}];
> r[t_] = r2[t] /. solution
> th[t_] = th2[t] /. solution
> si[t_] = si2[t] /. solution

> or (better yet):
>
> {r, th, si} = {si2, r2, th2} /. First@NDSolve[{si2'[t] == 2,
>      si2[0] == 0, th2'[t] == Sin[si2[t]]/r2[t], th2[0] == 0, r2'[
>            t] == Cos[si2[t]], r2[0] == 1}, {si2, r2, th2}, {t, 0, 25}]
>
> Bobby
>

```

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