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Re: Translating ODE from Matlab to Octave

From: Torsten
Subject: Re: Translating ODE from Matlab to Octave
Date: Tue, 26 Nov 2013 19:44:05 +0100
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On 26.11.2013 19:33, c. wrote:
> On 26 Nov 2013, at 18:53, Torsten <address@hidden> wrote:
>> And odepkg provides the mass matrix parameter "Mass" in case there might
>> be numerical issues with the inverse of M. I use ode45 on a regular
>> basis on octave and matlab systems (without code modifications).
> ode45 uses the one-step explicit RK45  method which is not a viable choice 
> for integrating stiff systems, 
> and even more so if the system to be integrated is a set of DAEs which may be 
> roughly considered as 
> "infinitely stiff" ODEs. 
> Indeed I see in the source code of ode45 [3] that an inversion of the mass 
> matrix is used, which cannot work for DAEs.
> There are other matlab compatible solvers in odepkg that are intended for 
> solving stiff problems, e.g. ode23s [1], 
> but I am quite sure ode23s won't work for DAEs, as I see in the code that an 
> inversion of the mass matrix [2]  is used in the algorithm.
> There are other solvers in odepkg that do work for DAEs [4] but I'm not sure 
> whether they are matlab compatible.
> The recomended solver to use for DAEs in matlab is ode15s [4], which is not 
> (yet?) implemented in Octave or Octave Forge, but
> the algorithm used by daspk is exactly the same as that of ode15s so I'd 
> recommennd using daspk for solving DAEs in Octave.
>> Torsten
> c.
> [1]
> [2]
> [3]
> [4] see the 5th table in the page 

You are right.

I did not want to recommend ode45 for this specific simulation case. I
just wanted to confirm your statement that odepkg provides a matlab
compatible interface. Sorry if my post was misleading.


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