ODE with dependent parameters

Hi everybody, I want to solve a system like the one below:

[dA/dt dB/dt]=( c1 c2 ; c3 c4+f(A) )*(A B)

f is of the form f=A/(A+q)

The problem is that I cannot easily reduce the function to coefficients. I want to use ode45 for this problem, and I just want to update the coefficient every timestep. I can program this myself, but for the large system I have to solve that would be a lot of work, and ode45 is easily able to solve large systems. Is there a method to do this?

Thanks! Gerrald

[Jan]

What is "(A B)"? Which coefficient do you want to change in every timestep? Which dimensions have A and B?