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MathGroup Archive 2000

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diff eqts and 3D curves

  • To: mathgroup at smc.vnet.net
  • Subject: [mg21878] diff eqts and 3D curves
  • From: macsoft <macsoft at ctrlaltdel.ch>
  • Date: Wed, 2 Feb 2000 22:54:34 -0500 (EST)
  • Organization: UNET/Urbanet NNTPcache news server
  • Sender: owner-wri-mathgroup at wolfram.com

Hi!

Q1:

I have a system of two non-linear 2nd-order differential equations in
terms of x(t), x'(t), x''(t), y(t), y'(t), t

The system is not very unstable, but near zero the values are out of the
range of the machine. I thought it wouldn't matter since I integrate
from t = 66 to 72 with initial conditions at t = 66, but I get this message:

NDSolve::"ndnum": "Encountered non-numerical value for a derivative at 
t == 2.524140890933554`*^-299."

Does Mathematica always intergate from 0 even if the range asked for is
far from 0? If so, how can I avoid that problem?
Since my solutions should all funnel to the same kind of behavior at
very large t, it is clearly unstable to integrate with final conditions!

Q2:

I wonder how I can plot a 3D curve, in particular the curve given by: (Re(f(t)),Im(f(t),t)

Thank you for your help!

macsoft


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