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solving differential equations

  • To: mathgroup at
  • Subject: [mg3484] solving differential equations
  • From: wilkinson at (Steven Wilkinson)
  • Date: Sat, 16 Mar 1996 22:39:28 -0500
  • Sender: owner-wri-mathgroup at


I have a system of ODE I wish to solve numerically of the form X'[t] =
F(X[t])/|F(X[t])| for a given function
        F : plane -> plane
and given intial conditions. NDSolve works well on this except where the
system is ill-behaved, in particular, where F = 0. I can replace this
system with another one that has equivalent solutions and is usually
well-behaved where F = 0. However, I don't want to make the replacement
unless I have to, and only near where F = 0. (I wish to construct a command
that gives the solution for an inputted function F.)

Is there any way possible to do this with NDSolve? In other words, as it
steps along have it check the value of F. If its magnitude ever gets too
close to 0, have it use the other system.

If that is not possible, does anyone have a solver package that I could
modify to do the above?

Steve Wilkinson
Dept of Math & CS
Northern Kentucky University
wilkinson at


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