What is a signal?
A signal is a function of time. A signal may represent a voltage or current in
a circuit, or a pressure wave (sound) in the air, or the wind velocity as a
function of time. It is represented as x[t], where t is time (with units of
seconds). The units of x depend on what one is modeling; examples would be
volts, amps, or often in signal processing, unspecified units.
Up to Signals and Sinusoids
Initializaton routines (ignore)