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Re: ode45 gives solution in the "Dark Side," but not in Octave

From: John B. Thoo
Subject: Re: ode45 gives solution in the "Dark Side," but not in Octave
Date: Wed, 2 Sep 2009 16:58:14 -0700

On Sep 2, 2009, at 11:28 AM, Thomas Treichl wrote:

John B. Thoo schrieb:
Hi. I have a question about using ode45 in Octave 3.2.2 (and OdePkg on Mac OS X 10.4.11) vs. in the "Dark Side" 7.4.0 (R2007a) (on a server ... Linux?). My code can be found here at the moment:
"run_twoway.m" executes the code.
Both Octave and the Dark Side solve the problem (i.e., do not return an error) to produce a solution u, and both give
 > size (u)
ans =
    8192    102
However, while I can plot the solution in the Dark Side, in Octave I can plot only the first four frames. In fact, in Octave I get NaN + 0.00000i from u(:,5) on. Why is that?
I would appreciate any hints.  Thanks.

Good question, I would say that you have a tricky problem and the solver gets into trouble ;) For a quick workaround: what happens if you use another solver like ode78? What about ode5r? I tried your example but get

  octave-3.2.0:10> run_twoway
  error: `heaviside' undefined near line 4 column 18
  error: called from:
  error:   /Users/Thomas/tmp/thoo/TwoWay/make_k.m at line 4, column 14
error: /Users/Thomas/tmp/thoo/TwoWay/run_twoway.m at line 20, column 3

Best regards


Hi, Thomas.  The function "heaviside" is part of SpecFun package:


I will try the other solvers you suggest.  Thanks.


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