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Re: [RE] Can someone tell me why NDsolve isn't working here?

• To: mathgroup at smc.vnet.net
• Subject: [mg45325] Re: [RE] Can someone tell me why NDsolve isn't working here?
• From: Ed Nowak <ewnowak at mfire.com>
• Date: Tue, 30 Dec 2003 04:14:31 -0500 (EST)
• References: <bsjl8s$23u$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Hi Miz,
Could you give the corrected system of 6 DAE equations, initial 
conditions, and parameter values? I am curious to see if Mathematica 5
will solve the problem as originally stated.
Thanks, Ed.

Mizrandir wrote:
> A month or so ago I posted a problem I had with a system of 6
> algebraic-differential equations. In case someone is interested, I did
> solve the  problem.
> 
> First of all, the equations had some minor mistakes (a wrong sign, a
> missing constant...). After correcting those I simplified within them
> until I was left with only these two equations:
> 
> x''[t] = L * (\[Theta][t]^2 * Sin[\[Theta][t]] - \[Theta]''[t] *
> Cos[\[Theta][t]]) / 8
> \[Theta]''[t] = 3 * (g * Sin[\[Theta][t]] - x''[t] * Cos[\[Theta][t]])
> / 2 / L
> 
> This two  equations can be simplified even more (by substitution of
> the first one into the second one) to get one diferential equation (of
> \[Theta][t]). After giving a numeric value to L and g, I soved it with
> NDSolve and with the \[Theta][t] function it gave me, I solved for
> x[t] too. I didn't solve for Rx, Ry, Fx and Fy because I wasn't
> interested in them (they were only needed to set up the equations).
> 
> miz.
>