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

[Thomas Treichl]

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:
>
> <http://ms.yccd.edu/~jb2/PickUp/twoway.zip>
>
> "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.
>
> ---John.

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

  Thomas