DSP - practical even or odd functions
Given a real signal, the choice of exactly which instant constitutes t = 0 is essentially arbitrary. So, for instance, if a signal occurs from 9:00:00 AM day before yesterday, to 9:00:02 AM the same day, you can set t = 0 at 9:00:01 and know what the signal was for t &lt; 0 as well as you do for t > 0.