A practical approach is to assign the current in the inductor L, i(t), and the voltage across the capacitor C, ec1 , as the state variables. The reason for this choice is because the state variables are directly related to the energy-storage element of a system. The inductor stores kinetic energy, and the capacitor stores electric potential energy. By assigning i(t) and ec(t) as state variables, we have a complete description of the past history (via the initial states) and the present and future states of the network.