I am facing a problem solving a ODE with a Runge-Kutta 4th order method:

The expression in order to solve is :

\begin{equation} Ay^{''}+By^{'}+Cy= Cu \end{equation}

\begin{equation} y =OUTPUT \end{equation}

\begin{equation} u=INPUT \end{equation}

We are using a sample time of 0.01s (with 0.001s sample time it does work), but the solver with some combinations of A,B and C does not converge. Then, we would like to know these combinations of A,B and C that make the method fail before start to using it.

Thanks in advance.