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## Re: DAE daspk solver problem

 From: Lazy_Tom Subject: Re: DAE daspk solver problem Date: Thu, 27 Oct 2016 18:50:28 -0700 (PDT)

```Sebastian Schöps wrote
>
> Lazy_Tom wrote
>> f(1) = xdot(1)-x(2);
>> f(2) = m*xdot(2)+x(5)*x(1);
>> f(3) = xdot(3)-x(4);
>> f(4) = m*xdot(4) + x(5)*x(3) +m*g;
>> f(5) = x(1)^2 + x(3)^2 - 1;
> I think there are a few typos, e.g., it should be -x(5)*x(3) in eq (4) but
> this is probably not the issue here. You are trying to solve a very
> difficult problem. This formulation of the pendulum is a DAE of index 3
> and afaik daspk can only deal with DAEs of index<3. There are many good
> books on this topic. If you are looking for a good free ressource, you may
> want to look at
> https://www.mathematik.hu-berlin.de/~steffen/pub/introduction_to_daes_497.pdf
> (page 2 and 13).
>
> Seb.

Hi Seb,

thanks for pointing out daspk max index, I wasn't aware. it spared a lot of

indeed, for some obscure reason I was convinced that the option "maximum
order" was actually "maximum index"... -.-

I don't know why DAE solvers index capabilities are not reported in Octave
manual. Matlab at least tells you that you can go no further than index 1
(at least without doing some "magic"...)

about the paper you cited, yup, I'm aware of it and I agree, it is quite
nice.

Well, at least I'll gave it a try, I think that for DAE problems I'll move
to openModelica

Cheers,

Marco

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