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MathGroup Archive 2000

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Re: DSolve problems with system of ODEs. Out in pure notation?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg21725] Re: DSolve problems with system of ODEs. Out in pure notation?
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Wed, 26 Jan 2000 03:45:28 -0500 (EST)
  • Organization: Universitaet Leipzig
  • References: <200001210900.EAA06601@smc.vnet.net> <200001220753.CAA11688@smc.vnet.net> <86e8o3$fbv@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

you get back a corect analytical solution ? So what's you problem ?
Since you give a numerical matrix of your system and you don't like the
RootSum[]
objects you can simply

DSolve[{x'[t] == -0.036 x[t] + 0.0124 y[t] + 0.000035 z[t] + 49.3, 
      y'[t] == 0.0111 x[t] - 0.0286 y[t], 
      z'[t] == 0.0039 x[t] - 0.000035 z[t], x[0] == 0, y[0] == 0, 
      z[0] == 0}, {x[t], y[t], z[t]}, t] // N

force the numerical evaluation of the RootSum[]'s by N[]

Hope that helps
  Jens

"J.Guillermo Sanchez" wrote:
> 
> If I evaluate,
> 
> DSolve[{x'[t] == -0.036 x[t] + 0.0124 y[t] + 0.000035 z[t] + 49.3,
>     y'[t] == 0.0111 x[t] - 0.0286 y[t], z'[t] == 0.0039 x[t] - 0.000035
> z[t],
>     x[0] == 0, y[0] == 0, z[0] == 0}, {x[t], y[t], z[t]}, t]
> 
> I receive a massage like this
> (RootSum::"pfn" :
>     "(DSolve`DSolveDump`dysfunction$6[273147 + <<1>>...
> is not a pure function.).
> and them a out in pure notation.
> 
> But I want to receive the solution in standard notation.
> 
> Also the same sentece work fine in Mathematica 2.2.
> 
> Can anyone give a hand?


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