second-order ODE, convert symbolic representation into matlabFunction

Hi!

I my code a symbolic second order ODE is created. Because i want to solve the function with ode45 i transform the ODE into a system of first order ODEs.

All that works.

But: If the complexity an length of the ODE increases matlab takes a HUGE (up to hours) time to do "matlabFunction".

Here is the relevant part of my code([ ] is only explanation):

x     = sym('x%d',[n,1]); 
x     = sym(x,'real');
xdot  = sym('xdot%d',[n,1]);   %      
xdot  = sym(xdot,'real');
xddot = sym('xddot%d',[n,1]);  %    
xddot = sym(xddot,'real');

[...some stuff happens here]
xddot=[f(x1,x2,x3,....,xdot1,xdot2,xdot3,...] %<- something like that

func=matlabFunction(xddot,'vars',{'t',[x;xdot]}); %<- slow!

any suggestions how to speed up things a little bit?

Greetings Alex