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MathGroup Archive 2004

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AW: "Rubbish" integration outputs

  • To: mathgroup at smc.vnet.net
  • Subject: [mg45730] AW: [mg45724] "Rubbish" integration outputs
  • From: Klamser at t-online.de (Peter Klamser)
  • Date: Thu, 22 Jan 2004 03:37:31 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

the arbitrary variables k$XXXX are produced, because the result of your ODE
contains derivates of the e^x^2 function, Mathematica can not substitute
with Erf[x] neither integrate.

So you have to use a numerical solution with NDSolve.

Regards

Peter

-----Ursprüngliche Nachricht-----
Von: Iwonder [mailto:yssual at yahoo.com]
Gesendet: Mittwoch, 21. Januar 2004 10:55
An: mathgroup at smc.vnet.net
Betreff: [mg45724] "Rubbish" integration outputs


Hi,

I always find me in troubles when integrating ODE that I think Mathematica
should be able to do. It's all right for the very simplest, but consider for
instance the following:

\!\(DSolve[\((x + 2  x\^2 + x\^3)\) \(y'\)[x] + \(x\^2\) \(y''\)[x] == A, y,
    x]\)

'A' a constant. Well, the problem is that I don't even the clue that
Mathematica *cannot* integrate it, there is some output with gibberish, like
K$14646 and the like (those are intermediary variables I guess). So what is
wrong? Is Mathematica expected to return such outputs?

Cheers.





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