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Re: DSolve for a system of 3 equations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg36299] Re: DSolve for a system of 3 equations
  • From: guillerm at aida.usal.es (Guillermo Sanchez)
  • Date: Fri, 30 Aug 2002 01:19:26 -0400 (EDT)
  • References: <akkctj$81o$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Neil,

They are not a general analitical solution for a system of ODE with 3
or more variables where all coffs. are parameters. I have a package
for solving SODE. Perhaps you can find it useful.

http://www.mathsource.com/Content/WhatsNew/0211-554

Guillermo Sanchez

Neil Klepeis <nklepeis at uclink4.berkeley.edu> wrote in message news:<akkctj$81o$1 at smc.vnet.net>...
> I try to solve a three equation linear ODE system with constant 
> coefficients and Mathematica 3.0 (Intel/Linux) chokes (see below).
> 
> When I try the same thing on Mathematica 4.0 (Solaris) I get a very 
> strange result containing things like "E^x#1" OR "#1^2".
> 
> Am I doing something wrong, or is there a bug/problem with Mathematica.
> 
> Regards,
> Neil
> 
> 
> 
> -- Solving a Three Equation ODE system (Linear with Constant 
> Coefficients) with Mathematica 3.0 ----
> 
> INPUT:
> 
> DSolve[{y1'[x] + c11*y1[x] + c12*y2[x] +c13*y3[x] +c1==0,
>      y2'[x]+c21*y1[x]+c22*y2[x]+c23*y3[x]+c2==0,
>      y3'[x]+c31*y1[x]+c32*y2[x]+c33*y3[x]+c3==0,
>      y1[0]==y1i, y2[0]==y2i, y3[0]==y3i},
>      {y1[x], y2[x], y3[x]}, x]
> 
> OUTPUT:
> 
> Eigensystem::"eivec":
>      "Unable to find eigenvector for eigenvalue \!\(Root[\(\(\(\(c13\\ 
> c22\\ \
> c31\) - \(c12\\ c23\\ c31\) - \(c13\\ c21\\ c32\) + \(c11\\ c23\\ c32\) + \
> \(\\[LeftSkeleton] 20 \\[RightSkeleton]\)\) &\), 1\)]\)."
> Eigensystem::"eivec":
>      "Unable to find eigenvector for eigenvalue \!\(Root[\(\(\(\(c13\\ 
> c22\\ \
> c31\) - \(c12\\ c23\\ c31\) - \(c13\\ c21\\ c32\) + \(c11\\ c23\\ c32\) + \
> \(\\[LeftSkeleton] 20 \\[RightSkeleton]\)\) &\), 2\)]\)."
> Eigensystem::"eivec":
>      "Unable to find eigenvector for eigenvalue \!\(Root[\(\(\(\(c13\\ 
> c22\\ \
> c31\) - \(c12\\ c23\\ c31\) - \(c13\\ c21\\ c32\) + \(c11\\ c23\\ c32\) + \
> \(\\[LeftSkeleton] 20 \\[RightSkeleton]\)\) &\), 3\)]\)."
> General::"stop":
>      "Further output of \!\(Eigensystem :: \"eivec\"\) will be suppressed \
> during this calculation."


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