Hi

I have to solve a 2nd order differential equation system(9*9) in matlab and I have some problems with it:

eq1=f(x1,x2,.....,x9,x1'',x2'',....,x9'')=0

.

.

eq9

they are linear equations.

The initial conditions: x1(0)=x2(0)=....x9(0)=0, x1'(0)=.....x9'(0)=0

One of the problem is when I want to solve them by ode45 ,it needs to introduce x1'', x2'' ,.... in each equation.

what should I do? please help me.