second-order ODE, convert symbolic representation into matlabFunction

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Alex 2012-1-19

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/26489-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!