On 7 Feb., 12:26, Torsten <Torsten.Hen...@umsicht.fraunhofer.de>
wrote:
> On 7 Feb., 11:30, "Michal Lukac" <michal.lu...@fstroj.uniza.sk> wrote:
>
> > > A couple of questions: In the notation "x4.b.sin(x1pi)" I assume the dot indicates multiplication, so why isn't it used in for example "x3cos(x2)"? Also why write "sin(x1pi)" 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 underhttp://www.unige.ch/~hairer/software.html
> I doubt that MATLAB's ode15i can handle index2 systems as it is
> required for your set of equations.
>
> Best wishes
> Torsten.
You may try to differentiate the last two algebraic equations twice
with respect to t and
solve the resulting ODEsystem using ODE15I.
But since you loose information by the differentiation, the errors in
x1, x2 and x3 may accumulate
such that your algebraic constraints from the last two equations get
violated during the integration.
Best wishes
Torsten.
