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From: Torsten Hennig on 4 Feb 2010 18:47
> Thanks Torsten for your answer.
>
> Acutally I have two equations (see below). But I
> thought I have to substitute equ (II) in (I) and then
> again only work with one equation.
>
> I)
>
>
> A-Bx(t)x'(t)-Cx'(t)^2-Dx(t)x''(t)=E-Fy(t)y'(t)-Gy'(t)
> ^2-Hy(t)y''(t)
> II) Q=x'(t)*a+y'(t)*b
>
> where A,B....,H,Q,a,b are constants.
>
> So, now again: Is it now possible to transform these
> two equations to a system of first order equations?
>
> Cheers,
> Franziska

The transformed system reads
x1' = x2
y1' = y2
0 = a*x2 + b*y2 - Q
-D*x1*x2' + H*y1*y2' =
E - F*y1*y2 - G*(y2)^2 - A + B*x1*x2 + C*(x2)^2

where x1 = x, x2 = x', y1 = y and y2 = y'.

You can solve this system directly without substitution
be using a solver of the ODE suite for which you
can specify a state-dependent mass matrix.

Best wishes
Torsten.
From: Franziska on 5 Feb 2010 09:40
> The transformed system reads
> x1' = x2
> y1' = y2
> 0 = a*x2 + b*y2 - Q
> -D*x1*x2' + H*y1*y2' =
> E - F*y1*y2 - G*(y2)^2 - A + B*x1*x2 + C*(x2)^2
>
> where x1 = x, x2 = x', y1 = y and y2 = y'.
>
> You can solve this system directly without substitution
> be using a solver of the ODE suite for which you
> can specify a state-dependent mass matrix.
>
> Best wishes
> Torsten.

Thanks Torsten!!!
It works!
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