[pstricks] Searching for a numeric solution for coupled differential equation systems of order 2

[Juergen Gilg]

Dear PSTricks list,

is there anybody out there, knowing about how to generate a PS code for 
"Runge-Kutta 4" to solve a "coupled differential equation system of 
order 2"?

There is the need for such a code to animate a double-pendulum in real 
time, following the coupled differential equations with the variables 
(\varphi_1, \varphi_2) and their derivatives like:

(1) 
l_1\ddot{\varphi}_1+\frac{m_2}{m_1+m_2}l_2\ddot{\varphi}_2\cos(\varphi_1-\varphi_2)-\frac{m_2}{m_1+m_2}l_2\dot{\varphi}_2^2\sin(\varphi_1-\varphi_2)+g\sin\varphi_1=0

(2) 
l_2\ddot{\varphi}_2+l_1\ddot{\varphi}_1\cos(\varphi_1-\varphi_2)-l_1\dot{\varphi}_1^2\sin(\varphi_1-\varphi_2)+g\sin\varphi_2=0

Any help is appreciated!!!

Many thanks for every hint,

Jürgen

-- 
Jürgen Gilg
Austr. 59
70376 Stuttgart

tel   0711 59 27 88
email gilg at acrotex.net