Property: Causal System
Definition: The system is causal such that it gives a zero output for the time variable t < 0.
Example that satisfies this property:
h(t)=u(t-1)*e^(-t)
For t<0, h(t)=0*e^(-t)=0; so this system is causal.
Example that doesn't satisfy this property:
h(t)=u(1-t)*e^(-t)
For t<0, h(t)=1*e^(-t)=e^(-t) not equal to zero; so this system is not causal.
