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MathGroup Archive 2003

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Can someone tell me why NDsolve isn't working here?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg44022] Can someone tell me why NDsolve isn't working here?
  • From: mizrandir at hotmail.com (Mizrandir)
  • Date: Sat, 18 Oct 2003 03:12:14 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello, Im trying to solve a system of 6 differential equations with
NDSolve but I can't get Mathematica to do it. I wrote:

R = 1;
M = 1;
L = 1;
NDSolve[{Rx[t] + Fx[t] == 2M x''[t], Ry[t] + Fy[t] == 0, 
    Fx[t] R == -M R x''[t], -Rx[t] == 
      M x''[t] + (M L \[Theta]''[t] Cos[-\[Theta][t]])/
          2 + (M L \[Theta]'[t]^2 Sin[-\[Theta][t]])/2, -Ry[
          t] == (M L \[Theta]''[t] Sin[-\[Theta][t]])/
          2 - (M L \[Theta]'[t]^2 Cos[-\[Theta][t]])/
          2, -(L Cos[\[Theta][t]] Rx[t])/2 + (L Sin[\[Theta][t]])/
          2 == (M L^2 \[Theta]''[t])/12, x[0] == 0, \[Theta][0] ==
Pi/2,
    Ry[0] == -M/2, Rx[0] == 0, Fy[0] == 5M/2, Fx[0] == 0}, {x,
\[Theta], Ry,
    Rx, Fy, Fx}, {t, 0, 1}]

And Mathematica gave me the following error:

NDSolve::"ndode": "Input is not an ordinary differential equation."

Does anybody know what am I doing wrong. Can I use Mathematica to
solve this?

Thanks in advance, miz.


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