Dynamic systems with continuous-time models in the form of differential equations possess memory. For systems with memory, knowledge of the system's inputs at a given point in time is insufficient to determine the state of the system at the same time. For example, a circuit with capacitors and inductors possesses memory. The instantaneous energy stored in the circuit is a function of the current state (capacitor voltages and inductor currents), which depends on the history of its sources (inputs) from the time when the complete state was last known.