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Subject: Re: DAE in matlab
Date: Tue, 7 Feb 2012 03:26:58 -0800 (PST)
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On 7 Feb., 11:30, "Michal Lukac" <michal.lu...@fstroj.uniza.sk> wrote:
> >   A couple of questions:  In the notation "x4.b.sin(x1-pi)" I assume the dot indicates multiplication, so why isn't it used in for example "x3cos(x2)"?  Also why write "sin(x1-pi)" instead of "-sin(x1)"?
>
> Yes, You are right the dot are multiplications, I wanted to write the equations more readable.... and hasn't crossed my mind to simplify the expressions.... sorry.
> These equations describe motion of a mechanism. I wrote them as I derive them from the drawing of mechanism. The last two eq. are constrains of the mechanism.
>
>  I tried to use ode15i, odebim(I have found here), but unsecesfull.  I'm not a mathematician... These equationas are DAE differential equations + algebraic equations.http://en.wikipedia.org/wiki/Differential_algebraic_equation
>
> I have' found something about index of DAE, but i don't understand well and the solvers solve the equations just of particular index.
> May be, I need to modify these euations a bit but I don't know how..
> When I tried to use ode15i and odebim I reduced the order of DE by substitutions
> d_y1 = dd_x,  d_y2 = d_x, ...etc...
>
> thanks.

There are specialized codes for the simulation of constraint
mechanical systems.
Take a look at the 'Mechanical Systems' section under
http://www.unige.ch/~hairer/software.html
I doubt that MATLAB's ode15i can handle index-2 systems as it is
required for your set of equations.

Best wishes
Torsten.