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MathGroup Archive 2003

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trouble solving partial DE

  • To: mathgroup at smc.vnet.net
  • Subject: [mg39919] trouble solving partial DE
  • From: karlo jolic <kjolic at swin.edu.au>
  • Date: Tue, 11 Mar 2003 02:39:02 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi everyone

I keeping getting the following error:

NDSolve::"deql": "The first argument must have both an equation and an \

initial condition."

when i try to solve the following second order partial differential
equation
(wherein the function u is a function of variables x and t):

NDSolve[{m*D[u[x, t], t, t] + 6*Pi*n*r*D[u[x, t], t] -
         0.5*mu*i*ndash*pm*((L - u[x, t])^2/(R^2 + (L - u[x, t])^2)^1.5
-
         1/(R^2 + (L - u[x, t])^2)^0.5 - (L + u[x, t])^2/(R^2 + (L +
u[x, t])^2)^1.5 +
         1/(R^2 + (L + u[x, t])^2)^0.5) == 0,
         u[L, 0] == L,
         D[u[L, 0], t] == 0},
         u, {x, 0, L}, {t, 0, 1}]

I have specified 2 initial conditions already, so i can't understand why
i get the error.

does anyone know whats the problem?

Thanks

Karlo
PS I'm relatively new at mathematica.



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