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

[John B. Thoo]

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:
> > <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

Hi, Thomas.

With ode78, I can plot up to three frames.  ode5r gives an error:

octave-3.2.2:11> run_twoway
error: `ode5r' undefined near line 36 column 11
error: called from:
error:   /Users/jbthoo/Desktop/NumMethPractice/MHD/TwoWay/ 
run_twoway.m at line 36, column 9
octave-3.2.2:11>

But you've given me an idea: I look in ~/octave/odepkg-0.6.7/, and  
see I also have ode23 and ode54.  Unfortunately,

With ode23, I can plot up to seven frames.
With ode54, I can plot up to four frames.

Thanks.

---John.