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MathGroup Archive 2000

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real valued solutions?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg23449] real valued solutions?
  • From: Robert <robert.schuerhuber at gmx.at>
  • Date: Wed, 10 May 2000 02:32:28 -0400 (EDT)
  • Organization: Vienna University of Technology, Austria
  • Sender: owner-wri-mathgroup at wolfram.com

i guess my problem is rather simple to solve, but i counld't figure it
out :-(

i'd like to solve ordinary differential equations with constant
coefficients with mathematica, where everything is real-valued. so the
solution is real-valued, too. how can i avoid the complex exponentials
in the solution?

e.g.

DSolve[{y''[x]-y'[x]+y[x]==0,y[0]==1,y'[0]==0},y[x],x]

gives

{{y[x]->Exp[-(-1)^2/3 x ( ... }}

as the result instead of the real-valued solution y[x]=Exp[x/2]
(Cos[Sqrt[3]/2 x]-1/Sqrt[3] Sin[Sqrt[3]/2 x).

robert







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