Explicit terms into an odefun

Hello everybody.

I am solving a system of ODE's. Let's suppose we are considering the equations:

x' + y' + x*y = f(t);
2x' + y' = g(t);
x(0)=x0;
y(0)=y0;

I know matlab can solve this without problems. I am considering this simple example only to make things as clear as possible.

I was wondering if it might be possible to express some terms explicitly. For example, might it be possible to evaluate the term "x*y" backwards?

I mean, is there any easy way to write the odefun so that the product "x*y" is evaluated backwards at each time step, as the multiplication between the values of x and y obtained for the previous (solved) time step?

For instance, at t=t1 this would mean "x*y" = "x0 * y0", and so on.

Thanks

Andrea