A piecewise continuous function of time. The value of a signal may include different matrix data types. An activation time domain is associated with each signal. The value of a signal is constant outside of its activation time domain.

A discrete-time signal is a special case of signal in which the time domain is reduced to isolated instants of time. A discrete-time signal is piecewise constant. A special case of discrete-time signal is a periodic signal.

Signals are associated with links in a model. An activation signal is a signal with no value.