Re: NDSolve, three 2-d order ODE, 6 initial conditions

• To: mathgroup at smc.vnet.net
• Subject: [mg115232] Re: NDSolve, three 2-d order ODE, 6 initial conditions
• From: michael partensky <partensky at gmail.com>
• Date: Tue, 4 Jan 2011 18:50:12 -0500 (EST)

```Thanks, Robert.
For w0=w1=10 I got the plot identical to yours.
However, with Mathematica 8 it is possible to find  the solutions for
*arbitrary *frequencies
(which is justified physically), while Mathematica 7 fails in many cases (according to your observation- practically everywhere, except for the  integers).

Hence,  this is indeed a bug of 7. which is fixed in 8.

It would be great to hear from Wolfram developers involved in this
improvement. Was it documented somewhere?

Best
Michael

On Tue, Jan 4, 2011 at 2:41 PM, Dr. Robert Kragler <kragler at hs-weingarten.de
> wrote:

>  Hi Michael,
> what I found out (just by doing) is that the system becomes indeterminate
> if you replace the frequencies w, w0 and w1 by real values. But if you
> approximate w0 = 9.8 by 10 (integer!) then it works. The velocities
> v0x,v0y,v0z are uncritical with respect to the change real <=> integer. The
> same is true for t-interval {t1,t2}.
> Regards,
>                     Robert
>
> Am 04.01.2011 19:10, schrieb michael partensky:
>
> sol = ndSol[10, 9.8, 1, 0, 0, 0, 1, 0, 1, 0, 30.]
>
>
> --
> Prof. Dr. Robert Kragler
> Hasenweg 5