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MathGroup Archive 2003

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Re: I have put "==" in every equation I have in NDSolve, why it keeps telling me they are not equations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg44587] Re: I have put "==" in every equation I have in NDSolve, why it keeps telling me they are not equations
  • From: drbob at bigfoot.com (Bobby R. Treat)
  • Date: Sat, 15 Nov 2003 02:05:15 -0500 (EST)
  • References: <bmqplo$rhb$1@smc.vnet.net> <bmt8eg$87l$1@smc.vnet.net> <3FB43093.4000104@physics.ucsb.edu> <bp299p$38b$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

My Mathematica 5.0 kernel doesn't seem to have that problem. I'd suggest
eliminating the new-lines embedded in the equation list, as that can
sometimes lead to problems.

I get this error instead:

NDSolve::underdet: There are more dependent variables, {p[y, t, x],
u[y, t, \
x], v[y, t, x]}, than equations, so the system is underdetermined.

Bobby

Xiaochao Xu <xiaochao at physics.ucsb.edu> wrote in message news:<bp299p$38b$1 at smc.vnet.net>...
> NDSolve::deqn: "Equation or list of equations expected instead of 0 in the \
> first argument
> 
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>             Sin[x]*Cos[y]*\[PartialD]\_y u[t, x, y] - 
>             Sin[x]*Sin[y]*u[t, x, y] + Cos[x]*Cos[y]*v[t, x, y] - 
>             Sin[x]*Cos[x]/c2*
>               p[t, x, y] == \(-\[PartialD]\_x p[t, x, 
>                 y]\), \ \[IndentingNewLine]\[IndentingNewLine]\[PartialD]\_t 
>                 v[t, x, y] + Cos[x]*Sin[y]*\[PartialD]\_x v[t, x, y] - 
>             Sin[x]*Cos[y]*\[PartialD]\_y v[t, x, y] - 
>             Cos[x]*Cos[y]*u[t, x, y] + Sin[x]*Sin[y]*v[t, x, y] - 
>             Sin[y]*Cos[y]/c2*
>               p[t, x, y] == \(-\[PartialD]\_y p[t, x, 
>                 y]\), \[IndentingNewLine]\[IndentingNewLine]\[PartialD]\_t p[
>                 t, x, y] + 
>             c2*\((\[PartialD]\_x u[t, x, y] + \[PartialD]\_y v[t, x, y])\) + 
>             Cos[x]*Sin[y]*\[PartialD]\_x p[t, x, y] == 
>           Sin[x]*Cos[
>               y]*\[PartialD]\_y p[t, x, 
>                 y], \[IndentingNewLine]\[IndentingNewLine]u[0, x, y] \[Equal] 
>           0, v[0, x, y] == 0, p[0, x, y] == 0, 
>         u[t, 0, y] == 
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>         v[t, 0, y] == 0, 
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>         u[t, x, 1000] == 0, v[t, x, 1000] == 0, p[t, x, 1000] == 0, 
>         u[t, x, \(-1000\)] == 0, v[t, x, \(-1000\)] == 0, 
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