How do I add in external equations in ODE45 simulation?

Hello!

This is my state space model:

// State space
  der(x1) = x2;
  m1*der(x2) = -k1*(x1 - x3) + Pp*Ap*10 - Pm*Am*10 -b1*(x2 - x4) - gamma*x2;
  der(x3) = x4;
  M*der(x4) = k1*(x1 - x3) - k2*(x3 - L2*sin(x5)) + b1*(x2 - x4) - M*g*mu*x4;
  der(x5) = x6;
  1/3*m2*L2^2*der(x6) = L2*k2*(x3 - L2*sin(x5)) - k3*x5 - b2*x6 + L2/2*m2*g*sin(x5);

And this is my external functions who gives values to the state space model. How do I include this inside the ODE45 function?

// Dynamic flow
Qin = 15*R1*sqrt(P - Pp);

// Dynamic pressure
Pp = beta/(Ap*x1)*(Qin - 6*Ap*x2);
Pm = beta/(Am*(L1 - x1))*(6*Am*x2 - 6*Am*x2*R2);

This is probably very easy to do, but I don't know how to do that.

[Star Strider]

That does not look like MATLAB syntax.

Please post your MATLAB code.

[Daniel]

I don't have a MATLAB code. This is a OpenModelica code. The only who differ is the der() command. der() is the derivative.